As far as I remember, I believe I have answered the questions. I didn't know the questions required yes or no answers only because these questions can be either the yes or no type or the long answer type. Sorry.
Once again: The oppinion "Electronics is Simple" is an oppinion based on the type of thinking applied in Electronics design and is what knowledge I have in electronics is 100% irrelevant. Psychlogists do not care what Electronics is. They follow the explanations of the designer to EVALUATE what type of thinking is necessary and how much. US was one of the leaders in this field mainly in the 60's.
So, one may not know anything of electronics but may know how to eveluate human thinking which neither of us is qualified to do but may express any oppinion one wants.
I will talk only in regards to the forum: Due to reasons which I do not want to discuss with you all, I have been unable to build anything else except the standard and simple pre amplifier which I have posted links to. AGAIN: THIS IS NOT IMPORTANT FOR DEFENCE OF "ELECTRONICS IS SIMPLE". This is important because I want to build some stuff but am unable to do so as I am unable to follow the forum often and for long.
Please, note: this forum is NOT the only thing I do and I have far more important and difficult tasks (not with electronics, do not think I go superiority complex).
Please, also note: this schematic is the most standard one in the world.
Once again: The oppinion "Electronics is Simple" is an oppinion based on the type of thinking applied in Electronics design and is what knowledge I have in electronics is 100% irrelevant. Psychlogists do not care what Electronics is. They follow the explanations of the designer to EVALUATE what type of thinking is necessary and how much. US was one of the leaders in this field mainly in the 60's.
So, one may not know anything of electronics but may know how to eveluate human thinking which neither of us is qualified to do but may express any oppinion one wants.
I will talk only in regards to the forum: Due to reasons which I do not want to discuss with you all, I have been unable to build anything else except the standard and simple pre amplifier which I have posted links to. AGAIN: THIS IS NOT IMPORTANT FOR DEFENCE OF "ELECTRONICS IS SIMPLE". This is important because I want to build some stuff but am unable to do so as I am unable to follow the forum often and for long.
Please, note: this forum is NOT the only thing I do and I have far more important and difficult tasks (not with electronics, do not think I go superiority complex).
Please, also note: this schematic is the most standard one in the world.
SSB,
The purpose of my questions was to try to lead the discussion in a logical direction.
That direction depending on what you said.
If you read here, you will see that there are people well schooled in electronics, from all aspects. Including self-taught, and school taught.
You will see that there are numerous discussions and analysis of what we here commonly refer to as "crossover distortion". There are amplifiers whose main intention is to keep transistors in the output stage from turning off, to limit the effects of this problem. (and numerous other "solutions" being considered)
There are numerous threads that discuss the effects of feedback upon overall amplifier performance.
I asked you for a specific DISTORTION FIGURE for your "perfect" amplifier.
One reason for this is that there are multiple discussions on the audibility of absolute distortion levels, as measured. How little distortion is sufficient?
Do you know about Hawksford?
Some designs have vanishingly low distortion figures.
Are you aware that there are opamps available today that have as much as two orders of magnitude LOWER distortion than the TL0 series that you are talking about??
You have posted to a forum that has a wide range of participants, from neophytes to full bore experts who have spent decades working out the subtle problems found in designing and engineering and then BUILDING actual working units. I think nobody I have seen so far here minds anyone saying things that turn out to be off base or even outright wrong. Where you might find that people become ill-humored if the person posting doesn't or isn't able to respond in a constructive way.
I think that you are trying to share your thoughts and ideas with others, but to do that successfully it's important to not only reply clearly and concisely, but to not make big broad claims unless you are prepared to back them up with really solid facts and experience.
The fact that you say you can not build anything is a difficulty, since the basic theory does not always reveal deeper and more subtle things. There is more complex theory that speaks to some of these subtle things, but that requires extremely advanced mathematical models and significant complexity. Today much, but not ALL of that complexity has been encapsulated by some very educated and smart people into one or more of the "SPICE" simulators. They yield information back that no amount of standard paper and pencil work is likely to reveal, and they do it VERY quickly. If you can not build, you need to simulate - that at least gets you into the ballpark, if not all the way around the bases.
Here, read this, it's just one idea with some exposition:
simulation-analysis-several-unique-allison-based-output-stages
SSB, simple electronics is simple, advanced electronics is not simple and is full of subtlety. Things simply do NOT work exactly as expected, and nothing is "perfect". One has to balance between what you want and what you actually can get.
_-_-bear
_-_-bear
The purpose of my questions was to try to lead the discussion in a logical direction.
That direction depending on what you said.
If you read here, you will see that there are people well schooled in electronics, from all aspects. Including self-taught, and school taught.
You will see that there are numerous discussions and analysis of what we here commonly refer to as "crossover distortion". There are amplifiers whose main intention is to keep transistors in the output stage from turning off, to limit the effects of this problem. (and numerous other "solutions" being considered)
There are numerous threads that discuss the effects of feedback upon overall amplifier performance.
I asked you for a specific DISTORTION FIGURE for your "perfect" amplifier.
One reason for this is that there are multiple discussions on the audibility of absolute distortion levels, as measured. How little distortion is sufficient?
Do you know about Hawksford?
Some designs have vanishingly low distortion figures.
Are you aware that there are opamps available today that have as much as two orders of magnitude LOWER distortion than the TL0 series that you are talking about??
You have posted to a forum that has a wide range of participants, from neophytes to full bore experts who have spent decades working out the subtle problems found in designing and engineering and then BUILDING actual working units. I think nobody I have seen so far here minds anyone saying things that turn out to be off base or even outright wrong. Where you might find that people become ill-humored if the person posting doesn't or isn't able to respond in a constructive way.
I think that you are trying to share your thoughts and ideas with others, but to do that successfully it's important to not only reply clearly and concisely, but to not make big broad claims unless you are prepared to back them up with really solid facts and experience.
The fact that you say you can not build anything is a difficulty, since the basic theory does not always reveal deeper and more subtle things. There is more complex theory that speaks to some of these subtle things, but that requires extremely advanced mathematical models and significant complexity. Today much, but not ALL of that complexity has been encapsulated by some very educated and smart people into one or more of the "SPICE" simulators. They yield information back that no amount of standard paper and pencil work is likely to reveal, and they do it VERY quickly. If you can not build, you need to simulate - that at least gets you into the ballpark, if not all the way around the bases.
Here, read this, it's just one idea with some exposition:
simulation-analysis-several-unique-allison-based-output-stages
SSB, simple electronics is simple, advanced electronics is not simple and is full of subtlety. Things simply do NOT work exactly as expected, and nothing is "perfect". One has to balance between what you want and what you actually can get.
_-_-bear
_-_-bear
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Hi, i think your design doesn't quite match up the the design goals...
I see it uses a darlington-pair class-AB output stage that isn't biased and that will induce a large crossover distortion (+/-1.3V), and the switches in the middle will make pulses when switched, so a muting device should be used when switching inputs.
I see it uses a darlington-pair class-AB output stage that isn't biased and that will induce a large crossover distortion (+/-1.3V), and the switches in the middle will make pulses when switched, so a muting device should be used when switching inputs.
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Updated Documentation
ATTENTION: THERE IS A POSSIBILITY TO SHORT THE OUTPUTS OF THE PRE AMPLIFIER WITH THIS ARRANGEMENT OF THE SWITCHES. TL084 ALLOWS FOR THIS BUT THIS MUST NOT BE USED. 10K RESISTORS MAY BE CONNECTED TO THE OUTPUTS OF THE PREAMPLIFIERS AND THEN A BUFFER MUST BE PUT AT THE INPUT OF EACH OF THE ADDERS TO REMEDY THIS PROBLEM.
Attention: Huge input impedance input. Capacitor decoupled outputs (capacitor in series to the input) must not be connected to the amplifier UNLESS a resistor with a value of 1M to 10M is connected in parallel to the input!
Keep all resistors and potentiometers with values approximately 1K to approximately 10K unless necessary to be higher. Thus less noise gets through. (Filters may require higher resistance because of lack of high value capacitors or difficulty in finding such or large size.
Do phase analysis.
Introduction
The universal audio amplifier uses standard electronics circuitry only and is built with components largely available in the local stores.
The goal has been to create an inexpensive ・analogue studio・, i. e. a multi channel audio ・system・ which has an independent for each channel pre amplifier with separate adjustable ・pre・ gain, an adder (mixer) which allows for signal combination into two output channels to achieve stereo sound. The amplifier has been designed to be powerful enough to satisfy the general purpose home needs and may be found useful for rehearsals, garage bands, outdoor performance, parties, etcetera.
This is a simple, standard electronic circuitry, off the shelf part, inexpensive and may be found useful universal audio amplifier which allows for most any configuration of the 4 channels. All can be made mono and displayed on one of the stereo outputs only, or on the two stereo outputs. Any can be combined with any and displayed on any of the two outputs. Thus, a possible application is to play music from a released song on the two channels in stereo fashion while playing the solo and displaying this on one of the outputs and singing and displaying the voice on the other. Or the music can play on one of the channels in mono fashion while the guitar and the voice are on the other.
This is achieved very simply by simple configuration single pole double throw switches as well as a few on off switches.
Principle
Power Supply:
Two standard off the shelf 110V AC to 18V AC, 1.85A transformers, T1 and T2, have been used to achieve a three point 36V DC, 1.85A (67W) power supply. These are not available in the general purpose stores, otherwise.
The inputs to the transformers (primary) have been paralleled with the outputs (secondary) put in series. Two standard 2A bridges, B1 and B2 rectify the two 18V voltages. In case of lack thereof, these can be made by 8 simple 2A diodes. The voltages at the output of the bridges are expected to be 18V ・ 2 * 0.7V = 16.6V. The voltages are averaged by the power supply filtering capacitors C01 and C05 and the RMS voltages are achieved. C02 through C04 and C06 through C08 are to filter spikes of switching noise, transients, etcetera and are chosen to be throughout the standard capacitive range without defined values. They can range 1µF, 1nF and 100pF, all >=18V, for example. A good idea is to keep: C02=C06; C03=C07; C04=C08.
C01=C05=220µF, >=18V or as big as possible electrolytic capacitors. The greater the value the better the filtering of the ripple effect.
The array of capacitors is something which I have made up and you are not expected to follow. Simply, do not install C02 through C04 and C06 through C08. To save more money and room, you may install only one capacitor between Vcc and Vee with as big as possible value and rated at >=36V. Huge 3.3mF (milifarads) capacitors are available at very inexpensive price these days at the local shops. Their diameter is like a coffee mug with 1・ height.
The negative of one of T1 is connected to the positive of T2 to achieve the middle point (ground).
Buffers:
Four independent channels are buffered by OA1 through OA4. All operational amplifiers are TL084 or parts thereof.
Resistors R11 through R14 are for protection with a typical value of 10K and may be unequipped for noise reduction purposes thus exposing the JFET inputs of OA1 through OA4 to the environment.
Resistors of the same value may be put in the feedback (not logical feedback resistors) just to equalise the bias which is not necessary for sound because the bias is either DC or incredibly slowly changing and will be filtered thereafter. This is supposed to be incredibly small in mother operational amplifiers and, in not so high gain amplification, these are not supposed to bring the operational amplifiers to saturation.
TL084 is internally compensated for unity gain stability and may not be further compensated. Most modern operational amplifiers are although some manufacturers may still make uncompensated operational amplifiers because of the faster speed and stable operation at gains higher than one. A phase compensator (a resistor and capacitor) are needed to be installed at the provided pins of these. Most likely, none of you would use these operational amplifiers because TL084 as well as most modern operational amplifiers are fast enough, definitely more than enough for general purpose sound amplification. TL084 has a Unity Gain BandWith (UGBW), a. k. a. frequency of transmission ft, a. k. a. transmission frequency at 3MHz, which makes amplification with a gain of 150 possible with performance at the audio range 20Hz to 25KHz.
A VERY GOOD IDEA IS TO PUT HIGH PASS FILTERS WITH CUT OFF FREQUENCIES OF 20Hz AFTER THE BUFFERS AND BEFORE THE PREAMPLIFIER. I haven・t yet because I am afraid from noise I may when I become calm.
Pre Amplifier:
The signals enters the preamplifiers built around the operational amplifiers OA21 through OA24 (TL084). Pay attention on the design of the pre amplifiers by non inverting circuit decisions. This means there will always be a gain of at least 2 regardless of the value of the potentiometers P21 through P24 unless these are off to big potentiometers (not sure whether these are available), i. e. potentiometers which can be switched off (infinite resistance), and, when they are switched on, they would immediately go to their maximal resistance as opposed to 0, as most of them may be.
Please, pay attention on something more important: On one hand, the non inverting amplifier circuit is preferable because of the huge input impedance but, on the other hand, the previous stage (the buffers in this case) cannot get any current through which may lead to a non linearity distortion. Hence, most people prefer the inverting amplifier circuit. You are very welcome to switch to this. Also, the inverting amplifier schematics would go from 1 to the maximal gain which may be important for rare cases where the output voltage must not be high and the input voltage is unknown, hence the user is supposed to turn the gain down and gradually increase the gain (in case necessary) until the desired level for a specific application.
Something which I consider a great disadvantage of the inverting preamplifier circuit but all of the rest say there isn・t such, is the inability to ground the potentiometer of the non inverting preamplifier circuit. Again, I am probably one of a few who claims this and you are not expected to follow. I am afraid from these ・antennas・, called potentiometers more than Jesus from the cops. Also, most would tell you say, a pot in the R1 circuit of the inverting amplifier circuit goes to low resistance of the previous stage and can・t pick too much noise. True, the noise would rather go to ground through the low output impedance of the previous stage but the other end of the resistor is in the feedback and any noise in the feedback would force the operational amplifier to adjusts its output accordingly to accommodate the noise just the same as the operational amplifier does to accommodate the feedback current (the current through R1 and R2 of the inverting amplifier circuit).
Anyways, I have decided to use the non inverting circuit and thus the buffers may be skipped because of the huge input impedance of the non inverting circuit, mainly in low gain application. The lower the gain, the more deep the feedback, the more like but not the same the amplifier performs like the buffer circuit. The less overall gain and the higher the open amplification (open gain, when the operational amplifier IC is not feedbacked), the higher the input impedance and the lower the output impedance.
I, however, prefer to keep the buffers because I am sick and tired of lousy sources of electrical signals. However, when known every operational amplifier used introduces non linearity distortions as well as noise, you may as well skip as much circuitry as you wish. For example the buffers.
Anyways, the pre amplifiers are built around the operational amplifiers OA21 through OA24 (TL084), resistors R211 through R241 (1K) and R212 through R242 (13K), capacitors C21 through C24 (470pF, >=18V) and potentiometers P21 through P24 (10K, >=1/4W (1/2W standard)). The capacitor values are much higher than the parasitic capacitors of the operational amplifier (5pF) and thus the parasitic capacitors would not affect the value of the cut of frequency.
Capacitors C21 through C24 are for pseudo filtering of frequencies higher than 25KHz. Real filtering is not possible because, at best, the high frequencies will be repeated at the output with a gain of 1 because of the gain function of the non inverting amplifier circuit:
G = 1 + R2x2 / R2x1
Even when R2x2 = 0, G is still equal to 1 and not to 0.
I・ve heard some people would even use a capacitor in series to the positive input of the non inverting amplifier circuit. This would stop the DC component with a cut off frequency of almost 0. Almost 0 because of the huge input resistance of the non inverting amplifier circuit:
fc = 1 / (2・ﾎRC)
fc ~ 0 when R -> ・・
However, this is NOT a good idea because the capacitor would stop the bias DC current on one of the pins (positive) only and there would not be compensation of the bias current on the other pin but most importantly because the capacitor would start charging by the DC component and this capacitor will become a source of input DC voltage to the non inverting amplifier and would saturate the operational amplifier・s output. However, some of the operational amplifiers have huge open gain input impedance and to charge a capacitor to this level may as well take several years or decades.
I do NOT recommend this, though.
The full gain formula of the pre amplifier is:
G = 1 + (R2x2 || Xc) / (R2x1+P2x), where:
Xc = 1 / (j ・ﾖ C2x) = 1 / (2 ・ﾎ R2x2 C2x)
and
x replaces 1, 2, 3, 4.
When P2x = 0, then G = 1 + 13K / 1K = 14 (maximal gain of the preamplifier)
When P2x = max, then G = 1 + 13K / 11K = 2.18 (minimal gain of the preamplifier)
Thus, each channel would have own amplification. At present, no provision has been made to allow for adjustment of bass and treble of each of the channel individually. This can be done easily by copying the stereo bass and treble adjustment circuit towards the output of the schematics for and pasting this to each channel after the pre amplifier, for example.
Provision for taking the signals after the pre amplifiers has been carried out via the outputs: OutP1 through OutP4 (OutPx). Additional 4 capacitor decoupled outputs are provided.
Switches:
Every switch and every potentiometer as well as everything which sticks out of the PCB even when PCB mount is a noise ・antenna・. Sometimes these are necessary. A rule of thumb is to ground these or, when not possible, to connect them to a very low impedance as for example an output of an operational amplifier.
The switches are the most interesting part of the universal audio amplifier. Switches are not part of the electronics engineering but are rather a question of simple arrangement.
The schematics has been drawn with software which either doesn・t allow for a clearer depiction or I do not know how to do such.
Each channel has three primary switches connected. The output of each of the preamplifier goes to a primary switch which gives two choices, each of the choices selects another, secondary, switch which is connected to one of the adders (mixers). This way, each channel is selected to go to any of the two adders. The secondary switches are connected to the input of each of the address and allow for each input of each adder to either be connected to the primary switch or to ground. Then there is a tertiary switch which connects/disconnects the two inputs of the adders.
ATTENTION: THERE IS A POSSIBILITY TO SHORT THE OUTPUTS OF THE PRE AMPLIFIER WITH THIS ARRANGEMENT OF THE SWITCHES. TL084 ALLOWS FOR THIS BUT THIS MUST NOT BE USED. 10K RESISTORS MAY BE CONNECTED TO THE OUTPUTS OF THE PREAMPLIFIERS AND THEN A BUFFER MUST BE PUT AT THE INPUT OF EACH OF THE ADDERS TO REMEDY THIS PROBLEM.
In order to clarify this explanation,
Pre Amplifier -> Switch 1
Adder 1
OR
Adder 2
Adder 1 (Switch 2.1)
Pre Amplifier (in case allowed by the preamplifier switch 1)
OR
Ground
Adder 2 (Switch 2.2)
Pre Amplifier (in case allowed by the preamplifier switch 1)
OR
Ground
Adder Connection (Switch 3)
Two adder inputs connected to each other
OR
Two adder inputs disconnected from each other
MUST NOT DO THESE LOGICAL ANDS (ALL ANDS SIMULTANEOUSLY):
(S1 SWITCHED TO ADDER 1) AND (S2.1 SWITCHED TO PRE AMPLIFIER) AND (S2.2 SWITCHED TO GROUND) AND (S3 SWITCHED ON).
(S2 SWITCHED TO ADDER 2) AND (S2.1 SWITCHED TO GROUND) AND (S2.2 SWITCHED TO PREAMPLIFIER) AND (S3 SWITCHED ON).
So, the switches allow for each pre amplifier output to be disconnected or to be connected to any of the two adders (mixers) or to the two of them.
Thus any channel can be played mono on one speaker only, mono on the two speakers or to be switched off. When switched off, ground must be applied to the two adder inputs reserved for this pre amplifier. When any of the two adders are switched off of the pre amplifier, this unused adder must be switched to ground. Ground is important for noise reduction. The best, a dongle jack with connected pins must be inserted into the input jack sockets to ground the inputs entirely from the beginning.
Adder:
A simple inverting adder has been designed to play a mixer. In addition, filtering capabilities have been arranged to filter all frequencies which are not in the audible range of 20Hz to 25KHz. Can be simply rearranged for the highest frequency to be 20KHz.
Wikipedia claims the audible spectrum to be 20Hz to 20KHz stating some individuals mainly of an young age can hear frequencies above 20KHz. Most audio engineers claim this range to be 20Hz to 20KHz. Some would go to 21.something just in cases. I would, personally, prefer to set the audio range from 20Hz to 30KHz, mainly for analogue application. However, I have chosen 20Hz to 25KHz.
Two adders (one for each of the two channels of the stereo) have been built around OA31 and OA32 with resistors R311 through R341 and R411 through R441 and capacitors C311 through C341, resistors R32 and R42 and capacitors C32 and C42.
All resistors are 10K. Capacitors C311 through C341 as well as capacitors C411 through C441 are 820nF, >=18V. Capacitors C32 and C42 are 620pF.
The function of the adder is:
Uout=(Sum(Ui/Zi1))*Z2 where:
Ui: input vol;tages
Zi1 = R3i1 + 1/(2 ・ﾎ f C3i1) for one of the adders and Zi1 = R4i1 || 1/(2 ・ﾎ f C4i1) for the other
Z2 = R32 || 1/(2 ・ﾎ f C32) for one of the adders and Z2 = R42 || 1/(2 ・ﾎ f C42) for the other
When all of the Zi1 have the same values and this value is Z1,
Uout=Z2/Z1(Sum(Ui))
When Z1=Z2,
Uout=(Sum(Ui))
Z1 is equal to Z2 in the bandwidth of 10Hz to 25KHz where the values of Z are determined by the values of the resistors.
The phase shift of the invertor as well as the phase shift of the pre amplifier and the power amplifier have not been calculated.
Bass Treble Filters:
Bass filters are aranged with C41 = C42, R41 = R42, P41 = P42. The transfer formula gives the coefficient of the filter K:
K = 1 / ( 2 pi ( R + P ) C )
The values can be calculated and chosen by:
* When P = 0, fc = 20Hz
* When P = max, fc = 500Hz
Thus, unless I have made an error with arithmetics:
C41 = C42 = 2uF, non electrolytic, >= 18V, best >= 36V
R41 = R4 = 4K, 1/4W
P41 = P42 = 100K, 1/2W ( standard ). Even 1/4W would do.
Another configuration may be: 0.39uF, 20K, 500K (same voltage and power) for those who do not like large capacitors. Although grounded on one side, large potemtiometer would pick a lot of noise.
Treble filters are aranged around C51 = C52, R511 = R521, R512 = R522, P51 = P52. The transfer formula gives the coefficient of the filter K:
Call, for simplicity,
C51 = C52 = C
R511 = R521 = R1
R512 + P51 = R522 + P52 = R2
R512 = R522
P51 = P52
K = R2 / ( R1 + R2 ) * 1 / ( 2 pi ( R1 || R2 ) C )
The values can be calculated and chosen by:
* When P = 0, fc = 25KHz
* When P = max, fc = 8192KHz
Thus, unless I have made an error with arithmetics:
C51 = C52 = C = 0.36nF, >= 18V, best >= 36V
R511 = R521 = 100K, 1/4W
R512 = R522 = 20K, 1/4W
P51 = P52 = 100K, 1/2W ( standard ). Even 1/4W would do.
Problem: too much attenuation.Needs higher amplification. Loss of signal. The higher the gain the higher the distortion. Not a big deal in this case, though.
Power Output Stage:
More amplification has been provided at the power output stage. The reason to have amplification close to the input, provided by the pre amplifier, is not only to equalize the signal levels but also to allow for amplification as close to the input as possible in order for the rest of the electronics to deal with large signals and not to be affected by a possible noise to be picked up on the signals・ path throughout the circuitry. HOWEVER, this has a drawback: the lower the signals the operational amplifiers deal with, the lower the nonlinearity. Because of this noise / nonlinearity controversy, a provision of two gain adjustments (close to the input, at the preamplifier and close to the output, at the power stage) to allow for the user to make the compromise accordingly.
Engineers don・t like noise, musicians: nonlinearity. Take ones, hit the others. Thus an engineer / musician will always be hit or will be hit double. Or never.
Basically, this is a non inverting amplifier with Darlington common collectors at the output before the feedback. The common collectrors are an extension of the operational amplifier which provides power at the output. On one hand, the power transistors should be connected to a grounded metal enclosure which would act as a heath sink but then they will be away from the PCB ( unless they are mounted on the PCB and the PCB is positioned in such a way as for the transistors to be bolted to the enclosure ). When away from the PCB, the transistors have to be connected with wires which will pick up noise. Although the wires are connected to a low impedance, these would pick up some noise and the noise is injected straight after the strait track and into the feedback track. Noise in the feedback cannot be compensated for. This appears at the input directly and screws up the performance of the amplifier.
A capacitor is connected in parallel to the "R2" of the non inverting amplifier to provide for a pseudo filtering capabilities, this is the pseudo filter will filter down to a gain of 1 as opposed to a gain of 0 as is with the inverting operational amplifier. The capaitor resistor parallel pseudo cuts at 25KHz.
The transistors are in Darlingtons to ensure 50mA max operational amplifier can drive them in the worst case of current amplification ( hFE ) = 10 for TIP41B and TIP42B ( T12, T14, T22, T24 ) and 15 for TIP29B and TIP30B ( T11, T13, T21, T23 ). All together the current amplification is 150. Even at 6A RMS at the output, the operational amplifier has to provide 6 / 150 = 45mA RMS which is still OK.
Each transformer can provide 1.85A RMS. In this circuit, this is 1.85A from + to ground and 1.85A from - to ground. The loudspeakers are rated 50W, 8Ohm each. Even when the whole current is supplied to each speaker, this will see 1.85A RMS from + to ground and 1.85A RMS from - to ground. This makes 2 * 1.85 = 3.7A RMS. Thus the overall maximum power a speaker can see is 3.7^2 * 8 = 109.52W RMS. In order for this to happen, the voltage at the speaker has to be 29.6V RMS. Each of the transformers can provide 18V RMS. Thus the two transformers can provide 36V RMS.
The voltage after the bridge is ( 18 / 0.707 - 1.4 ) * 0.707 = 17V. Thus the voltage between the + and the - of the power supply is 34V.
The common collectors will repeat the voltage displayed at their input (when they can). The operational amplifiers are supplied with 34V and can theoretically swing their outputs from negative rail to positive rail minus 1.5V. This is from - 17V to + 15.5V. To keep the symetry, the maximum normal working voltage can be - 15.5 to + 15.5. This gives an RMS of 15.5 * 0.707 = 10.96V RMS for a pure sine wave. In the worst case, the operational amplifier can display negative saturation only, which is - 17V DC. A fully open transistor will consume Vce of 0.3V, in some cases more. Assume 0 consumption from the transistor to work the worst case out. Thus the speaker will see <= 17V RMS. At 17V, the speaker will get 2.125A which gives 36.125W which is below the maximum power of each of the speakers which is 50W. Thus the speakers will not be damaged by the amplifier.
HOWEVER, I think the best practice is to assume, somehow, caused by a damage to the circuitry, the whole power of the output is applied to the speaker, this is 36V at 1.85A which is 67W. This is dangerous for the speaker. I believe the speaker can take so much but is not rated for. 67W is only 100 * ( 67 - 50 ) / 50 = 34% higher then 50W. Usually, any equipment should be able to witstand at least 1/3 higher than the rated.
ONLY NON DARLINGTON COMMON COLLECTORS ARE DISCUSED BELOW. THE DIFFERENCE WILL BE NOTED AT THE END.
A transistor will consume 0 power when fully open and fully closed. ( Vce when fully open ignored. ) As the voltage Vce decreases, the current Ice increases. In the middle, the power consumption will be ( Vce / 2 ) * ( Ice /2 ) = Vce * Ice / 4. The question is whether this is the maximal optimum of the function voltage multiplied by current.
Anyways, each transistor will see less than or equal to 17V and 1.85A. When not divided by 4, this is 31.45W. When divided, this is 7.8625W, 8W. Either of these are below the TIP41 / 42B ratings.
A good way to calculate the maximum power poossible to be dissipated by a transistor is to assume the very worst case of maximum voltage and maximum current of the power supply can be applied to / through a transisitor. In this case, this is 36V * 1.85A = 67.86W which is approximately the power rating of 65W of TIP41 / 42B. So, the transistors will be OK, too.
In the normal circumstances, when the amplifier output becomes positive, one of the transistors will be open to the desired extend and the other one will be fully closed. The base emitter voltage Vbe will be 0.7V and the direction will be in conducting direction of one of the base emitter junction of one of the junctions and non conducting of the other. Thus, one of the transistors will take care of half of the speaker's work, giving the full amplitude voltage of the speaker ( connected to ground ), half of the RMS voltage of the speaker and half of the RMS current through the speaker. Thus each of the transistors will take care of half of the work and half of the power of the speaker.
In non Darlington, the operational amplifier output will swing between - ( 0.7V + uout) to + ( 0.7 + uout), where uout is the amplitude of the output. In Darlinton, the BE junction of the two transistors are in series, thus the "common" BE voltage will be 1.4V. Thus, the operational amplifier will swing from - ( 1.4 + uout ) to + ( 1.4 + uout ). However, the OA output can only swing from - 15.5 to + 15.5 in normal operations. Therefore, the loudspeaker voltage can swing from - 14.1V to + 14.1V. Thus, RMS of 14.1 * 0.707 = 10V in pure sine. The worst case is fully distorted ( rectangular / square ) voltage with RMS of 14.1. Even worse case is negative rail and positive rail minus 1.5V (TL084 can reach 1.5V below positive rail ONLY), - 17 to 15.5 with duty cycle 50% which gives ( 17 + 15.5 ) / 2 = 16.25V RMS. Of course, the very worst case is: 100% duty cycle for the negative rail or 17V DC which brings power of 17 ^ 2 / 8 = 36.125W. In normal work (symetrical), the maximum voltage the output would see is 14.1V square / rectangular and the maximum normal working power is 14.1 ^ 2 / 8 = 25W which is how an amplifier is supposed to be rated. In pure sine, the maximum normal working output is ( 14.1 * 0.707 ) ^ 2 / 8 = 100 / 8 = 12.5W. This is a parameter good to be displayed.
I have been making the mistake saying the output of the OA would swing - 0.7V to + 0.7V in non Darlington. Must be read - 0.7V to + 0.7V higher / lower than the output voltage.
In order to avoid or minimise the mistakes, this circuit has to be looked at as a single transistor non push pulled circuit and only one wave assumed.
To Do:
1. Put the capacitor decoupled output of the pre amplifiers
2. Put an extra resistor and a switch at the input to provide for a possibility to put a low value resistor for microphones in case so desired.
3. The best, use a multi switch ( rotary ) for the input. See whether there are any except the fat 18 position rotary switches. Arrange the switch as follows: strait connection to the source, high value resistor, low value resistor, ground ( although ground can be provided by the input jack sockets unless they are guitar ones ( 1 / 4 " )
4. Consider a possibility for a potentiometer at the input for those who insist on getting exact different resistance for a specific microphone.
5. Consider current to voltage convertors as input preamplifiers. Non inverting amplifier without R1. R1 can be switchable for voltage outputs. Or the whole input circuitry.
Schematics
All resistors are 5%, 1/4W. All capacitors are >=18V.
Universal Audio Amplifier
by Steven Stanley Bayes
I USUALLY MAKE A LOT OF MISTAKES, SO DO NOT TRUST WHAT YOU READ. YOU MUST CHECK ALL OUT.
Important NotesATTENTION: THERE IS A POSSIBILITY TO SHORT THE OUTPUTS OF THE PRE AMPLIFIER WITH THIS ARRANGEMENT OF THE SWITCHES. TL084 ALLOWS FOR THIS BUT THIS MUST NOT BE USED. 10K RESISTORS MAY BE CONNECTED TO THE OUTPUTS OF THE PREAMPLIFIERS AND THEN A BUFFER MUST BE PUT AT THE INPUT OF EACH OF THE ADDERS TO REMEDY THIS PROBLEM.
Attention: Huge input impedance input. Capacitor decoupled outputs (capacitor in series to the input) must not be connected to the amplifier UNLESS a resistor with a value of 1M to 10M is connected in parallel to the input!
Keep all resistors and potentiometers with values approximately 1K to approximately 10K unless necessary to be higher. Thus less noise gets through. (Filters may require higher resistance because of lack of high value capacitors or difficulty in finding such or large size.
Do phase analysis.
Introduction
The universal audio amplifier uses standard electronics circuitry only and is built with components largely available in the local stores.
The goal has been to create an inexpensive ・analogue studio・, i. e. a multi channel audio ・system・ which has an independent for each channel pre amplifier with separate adjustable ・pre・ gain, an adder (mixer) which allows for signal combination into two output channels to achieve stereo sound. The amplifier has been designed to be powerful enough to satisfy the general purpose home needs and may be found useful for rehearsals, garage bands, outdoor performance, parties, etcetera.
This is a simple, standard electronic circuitry, off the shelf part, inexpensive and may be found useful universal audio amplifier which allows for most any configuration of the 4 channels. All can be made mono and displayed on one of the stereo outputs only, or on the two stereo outputs. Any can be combined with any and displayed on any of the two outputs. Thus, a possible application is to play music from a released song on the two channels in stereo fashion while playing the solo and displaying this on one of the outputs and singing and displaying the voice on the other. Or the music can play on one of the channels in mono fashion while the guitar and the voice are on the other.
This is achieved very simply by simple configuration single pole double throw switches as well as a few on off switches.
Principle
Power Supply:
Two standard off the shelf 110V AC to 18V AC, 1.85A transformers, T1 and T2, have been used to achieve a three point 36V DC, 1.85A (67W) power supply. These are not available in the general purpose stores, otherwise.
The inputs to the transformers (primary) have been paralleled with the outputs (secondary) put in series. Two standard 2A bridges, B1 and B2 rectify the two 18V voltages. In case of lack thereof, these can be made by 8 simple 2A diodes. The voltages at the output of the bridges are expected to be 18V ・ 2 * 0.7V = 16.6V. The voltages are averaged by the power supply filtering capacitors C01 and C05 and the RMS voltages are achieved. C02 through C04 and C06 through C08 are to filter spikes of switching noise, transients, etcetera and are chosen to be throughout the standard capacitive range without defined values. They can range 1µF, 1nF and 100pF, all >=18V, for example. A good idea is to keep: C02=C06; C03=C07; C04=C08.
C01=C05=220µF, >=18V or as big as possible electrolytic capacitors. The greater the value the better the filtering of the ripple effect.
The array of capacitors is something which I have made up and you are not expected to follow. Simply, do not install C02 through C04 and C06 through C08. To save more money and room, you may install only one capacitor between Vcc and Vee with as big as possible value and rated at >=36V. Huge 3.3mF (milifarads) capacitors are available at very inexpensive price these days at the local shops. Their diameter is like a coffee mug with 1・ height.
The negative of one of T1 is connected to the positive of T2 to achieve the middle point (ground).
Buffers:
Four independent channels are buffered by OA1 through OA4. All operational amplifiers are TL084 or parts thereof.
Resistors R11 through R14 are for protection with a typical value of 10K and may be unequipped for noise reduction purposes thus exposing the JFET inputs of OA1 through OA4 to the environment.
Resistors of the same value may be put in the feedback (not logical feedback resistors) just to equalise the bias which is not necessary for sound because the bias is either DC or incredibly slowly changing and will be filtered thereafter. This is supposed to be incredibly small in mother operational amplifiers and, in not so high gain amplification, these are not supposed to bring the operational amplifiers to saturation.
TL084 is internally compensated for unity gain stability and may not be further compensated. Most modern operational amplifiers are although some manufacturers may still make uncompensated operational amplifiers because of the faster speed and stable operation at gains higher than one. A phase compensator (a resistor and capacitor) are needed to be installed at the provided pins of these. Most likely, none of you would use these operational amplifiers because TL084 as well as most modern operational amplifiers are fast enough, definitely more than enough for general purpose sound amplification. TL084 has a Unity Gain BandWith (UGBW), a. k. a. frequency of transmission ft, a. k. a. transmission frequency at 3MHz, which makes amplification with a gain of 150 possible with performance at the audio range 20Hz to 25KHz.
A VERY GOOD IDEA IS TO PUT HIGH PASS FILTERS WITH CUT OFF FREQUENCIES OF 20Hz AFTER THE BUFFERS AND BEFORE THE PREAMPLIFIER. I haven・t yet because I am afraid from noise I may when I become calm.
Pre Amplifier:
The signals enters the preamplifiers built around the operational amplifiers OA21 through OA24 (TL084). Pay attention on the design of the pre amplifiers by non inverting circuit decisions. This means there will always be a gain of at least 2 regardless of the value of the potentiometers P21 through P24 unless these are off to big potentiometers (not sure whether these are available), i. e. potentiometers which can be switched off (infinite resistance), and, when they are switched on, they would immediately go to their maximal resistance as opposed to 0, as most of them may be.
Please, pay attention on something more important: On one hand, the non inverting amplifier circuit is preferable because of the huge input impedance but, on the other hand, the previous stage (the buffers in this case) cannot get any current through which may lead to a non linearity distortion. Hence, most people prefer the inverting amplifier circuit. You are very welcome to switch to this. Also, the inverting amplifier schematics would go from 1 to the maximal gain which may be important for rare cases where the output voltage must not be high and the input voltage is unknown, hence the user is supposed to turn the gain down and gradually increase the gain (in case necessary) until the desired level for a specific application.
Something which I consider a great disadvantage of the inverting preamplifier circuit but all of the rest say there isn・t such, is the inability to ground the potentiometer of the non inverting preamplifier circuit. Again, I am probably one of a few who claims this and you are not expected to follow. I am afraid from these ・antennas・, called potentiometers more than Jesus from the cops. Also, most would tell you say, a pot in the R1 circuit of the inverting amplifier circuit goes to low resistance of the previous stage and can・t pick too much noise. True, the noise would rather go to ground through the low output impedance of the previous stage but the other end of the resistor is in the feedback and any noise in the feedback would force the operational amplifier to adjusts its output accordingly to accommodate the noise just the same as the operational amplifier does to accommodate the feedback current (the current through R1 and R2 of the inverting amplifier circuit).
Anyways, I have decided to use the non inverting circuit and thus the buffers may be skipped because of the huge input impedance of the non inverting circuit, mainly in low gain application. The lower the gain, the more deep the feedback, the more like but not the same the amplifier performs like the buffer circuit. The less overall gain and the higher the open amplification (open gain, when the operational amplifier IC is not feedbacked), the higher the input impedance and the lower the output impedance.
I, however, prefer to keep the buffers because I am sick and tired of lousy sources of electrical signals. However, when known every operational amplifier used introduces non linearity distortions as well as noise, you may as well skip as much circuitry as you wish. For example the buffers.
Anyways, the pre amplifiers are built around the operational amplifiers OA21 through OA24 (TL084), resistors R211 through R241 (1K) and R212 through R242 (13K), capacitors C21 through C24 (470pF, >=18V) and potentiometers P21 through P24 (10K, >=1/4W (1/2W standard)). The capacitor values are much higher than the parasitic capacitors of the operational amplifier (5pF) and thus the parasitic capacitors would not affect the value of the cut of frequency.
Capacitors C21 through C24 are for pseudo filtering of frequencies higher than 25KHz. Real filtering is not possible because, at best, the high frequencies will be repeated at the output with a gain of 1 because of the gain function of the non inverting amplifier circuit:
G = 1 + R2x2 / R2x1
Even when R2x2 = 0, G is still equal to 1 and not to 0.
I・ve heard some people would even use a capacitor in series to the positive input of the non inverting amplifier circuit. This would stop the DC component with a cut off frequency of almost 0. Almost 0 because of the huge input resistance of the non inverting amplifier circuit:
fc = 1 / (2・ﾎRC)
fc ~ 0 when R -> ・・
However, this is NOT a good idea because the capacitor would stop the bias DC current on one of the pins (positive) only and there would not be compensation of the bias current on the other pin but most importantly because the capacitor would start charging by the DC component and this capacitor will become a source of input DC voltage to the non inverting amplifier and would saturate the operational amplifier・s output. However, some of the operational amplifiers have huge open gain input impedance and to charge a capacitor to this level may as well take several years or decades.
I do NOT recommend this, though.
The full gain formula of the pre amplifier is:
G = 1 + (R2x2 || Xc) / (R2x1+P2x), where:
Xc = 1 / (j ・ﾖ C2x) = 1 / (2 ・ﾎ R2x2 C2x)
and
x replaces 1, 2, 3, 4.
When P2x = 0, then G = 1 + 13K / 1K = 14 (maximal gain of the preamplifier)
When P2x = max, then G = 1 + 13K / 11K = 2.18 (minimal gain of the preamplifier)
Thus, each channel would have own amplification. At present, no provision has been made to allow for adjustment of bass and treble of each of the channel individually. This can be done easily by copying the stereo bass and treble adjustment circuit towards the output of the schematics for and pasting this to each channel after the pre amplifier, for example.
Provision for taking the signals after the pre amplifiers has been carried out via the outputs: OutP1 through OutP4 (OutPx). Additional 4 capacitor decoupled outputs are provided.
Switches:
Every switch and every potentiometer as well as everything which sticks out of the PCB even when PCB mount is a noise ・antenna・. Sometimes these are necessary. A rule of thumb is to ground these or, when not possible, to connect them to a very low impedance as for example an output of an operational amplifier.
The switches are the most interesting part of the universal audio amplifier. Switches are not part of the electronics engineering but are rather a question of simple arrangement.
The schematics has been drawn with software which either doesn・t allow for a clearer depiction or I do not know how to do such.
Each channel has three primary switches connected. The output of each of the preamplifier goes to a primary switch which gives two choices, each of the choices selects another, secondary, switch which is connected to one of the adders (mixers). This way, each channel is selected to go to any of the two adders. The secondary switches are connected to the input of each of the address and allow for each input of each adder to either be connected to the primary switch or to ground. Then there is a tertiary switch which connects/disconnects the two inputs of the adders.
ATTENTION: THERE IS A POSSIBILITY TO SHORT THE OUTPUTS OF THE PRE AMPLIFIER WITH THIS ARRANGEMENT OF THE SWITCHES. TL084 ALLOWS FOR THIS BUT THIS MUST NOT BE USED. 10K RESISTORS MAY BE CONNECTED TO THE OUTPUTS OF THE PREAMPLIFIERS AND THEN A BUFFER MUST BE PUT AT THE INPUT OF EACH OF THE ADDERS TO REMEDY THIS PROBLEM.
In order to clarify this explanation,
Pre Amplifier -> Switch 1
Adder 1
OR
Adder 2
Adder 1 (Switch 2.1)
Pre Amplifier (in case allowed by the preamplifier switch 1)
OR
Ground
Adder 2 (Switch 2.2)
Pre Amplifier (in case allowed by the preamplifier switch 1)
OR
Ground
Adder Connection (Switch 3)
Two adder inputs connected to each other
OR
Two adder inputs disconnected from each other
MUST NOT DO THESE LOGICAL ANDS (ALL ANDS SIMULTANEOUSLY):
(S1 SWITCHED TO ADDER 1) AND (S2.1 SWITCHED TO PRE AMPLIFIER) AND (S2.2 SWITCHED TO GROUND) AND (S3 SWITCHED ON).
(S2 SWITCHED TO ADDER 2) AND (S2.1 SWITCHED TO GROUND) AND (S2.2 SWITCHED TO PREAMPLIFIER) AND (S3 SWITCHED ON).
So, the switches allow for each pre amplifier output to be disconnected or to be connected to any of the two adders (mixers) or to the two of them.
Thus any channel can be played mono on one speaker only, mono on the two speakers or to be switched off. When switched off, ground must be applied to the two adder inputs reserved for this pre amplifier. When any of the two adders are switched off of the pre amplifier, this unused adder must be switched to ground. Ground is important for noise reduction. The best, a dongle jack with connected pins must be inserted into the input jack sockets to ground the inputs entirely from the beginning.
Adder:
A simple inverting adder has been designed to play a mixer. In addition, filtering capabilities have been arranged to filter all frequencies which are not in the audible range of 20Hz to 25KHz. Can be simply rearranged for the highest frequency to be 20KHz.
Wikipedia claims the audible spectrum to be 20Hz to 20KHz stating some individuals mainly of an young age can hear frequencies above 20KHz. Most audio engineers claim this range to be 20Hz to 20KHz. Some would go to 21.something just in cases. I would, personally, prefer to set the audio range from 20Hz to 30KHz, mainly for analogue application. However, I have chosen 20Hz to 25KHz.
Two adders (one for each of the two channels of the stereo) have been built around OA31 and OA32 with resistors R311 through R341 and R411 through R441 and capacitors C311 through C341, resistors R32 and R42 and capacitors C32 and C42.
All resistors are 10K. Capacitors C311 through C341 as well as capacitors C411 through C441 are 820nF, >=18V. Capacitors C32 and C42 are 620pF.
The function of the adder is:
Uout=(Sum(Ui/Zi1))*Z2 where:
Ui: input vol;tages
Zi1 = R3i1 + 1/(2 ・ﾎ f C3i1) for one of the adders and Zi1 = R4i1 || 1/(2 ・ﾎ f C4i1) for the other
Z2 = R32 || 1/(2 ・ﾎ f C32) for one of the adders and Z2 = R42 || 1/(2 ・ﾎ f C42) for the other
When all of the Zi1 have the same values and this value is Z1,
Uout=Z2/Z1(Sum(Ui))
When Z1=Z2,
Uout=(Sum(Ui))
Z1 is equal to Z2 in the bandwidth of 10Hz to 25KHz where the values of Z are determined by the values of the resistors.
The phase shift of the invertor as well as the phase shift of the pre amplifier and the power amplifier have not been calculated.
Bass Treble Filters:
Bass filters are aranged with C41 = C42, R41 = R42, P41 = P42. The transfer formula gives the coefficient of the filter K:
K = 1 / ( 2 pi ( R + P ) C )
The values can be calculated and chosen by:
* When P = 0, fc = 20Hz
* When P = max, fc = 500Hz
Thus, unless I have made an error with arithmetics:
C41 = C42 = 2uF, non electrolytic, >= 18V, best >= 36V
R41 = R4 = 4K, 1/4W
P41 = P42 = 100K, 1/2W ( standard ). Even 1/4W would do.
Another configuration may be: 0.39uF, 20K, 500K (same voltage and power) for those who do not like large capacitors. Although grounded on one side, large potemtiometer would pick a lot of noise.
Treble filters are aranged around C51 = C52, R511 = R521, R512 = R522, P51 = P52. The transfer formula gives the coefficient of the filter K:
Call, for simplicity,
C51 = C52 = C
R511 = R521 = R1
R512 + P51 = R522 + P52 = R2
R512 = R522
P51 = P52
K = R2 / ( R1 + R2 ) * 1 / ( 2 pi ( R1 || R2 ) C )
The values can be calculated and chosen by:
* When P = 0, fc = 25KHz
* When P = max, fc = 8192KHz
Thus, unless I have made an error with arithmetics:
C51 = C52 = C = 0.36nF, >= 18V, best >= 36V
R511 = R521 = 100K, 1/4W
R512 = R522 = 20K, 1/4W
P51 = P52 = 100K, 1/2W ( standard ). Even 1/4W would do.
Problem: too much attenuation.Needs higher amplification. Loss of signal. The higher the gain the higher the distortion. Not a big deal in this case, though.
Power Output Stage:
More amplification has been provided at the power output stage. The reason to have amplification close to the input, provided by the pre amplifier, is not only to equalize the signal levels but also to allow for amplification as close to the input as possible in order for the rest of the electronics to deal with large signals and not to be affected by a possible noise to be picked up on the signals・ path throughout the circuitry. HOWEVER, this has a drawback: the lower the signals the operational amplifiers deal with, the lower the nonlinearity. Because of this noise / nonlinearity controversy, a provision of two gain adjustments (close to the input, at the preamplifier and close to the output, at the power stage) to allow for the user to make the compromise accordingly.
Engineers don・t like noise, musicians: nonlinearity. Take ones, hit the others. Thus an engineer / musician will always be hit or will be hit double. Or never.
Basically, this is a non inverting amplifier with Darlington common collectors at the output before the feedback. The common collectrors are an extension of the operational amplifier which provides power at the output. On one hand, the power transistors should be connected to a grounded metal enclosure which would act as a heath sink but then they will be away from the PCB ( unless they are mounted on the PCB and the PCB is positioned in such a way as for the transistors to be bolted to the enclosure ). When away from the PCB, the transistors have to be connected with wires which will pick up noise. Although the wires are connected to a low impedance, these would pick up some noise and the noise is injected straight after the strait track and into the feedback track. Noise in the feedback cannot be compensated for. This appears at the input directly and screws up the performance of the amplifier.
A capacitor is connected in parallel to the "R2" of the non inverting amplifier to provide for a pseudo filtering capabilities, this is the pseudo filter will filter down to a gain of 1 as opposed to a gain of 0 as is with the inverting operational amplifier. The capaitor resistor parallel pseudo cuts at 25KHz.
The transistors are in Darlingtons to ensure 50mA max operational amplifier can drive them in the worst case of current amplification ( hFE ) = 10 for TIP41B and TIP42B ( T12, T14, T22, T24 ) and 15 for TIP29B and TIP30B ( T11, T13, T21, T23 ). All together the current amplification is 150. Even at 6A RMS at the output, the operational amplifier has to provide 6 / 150 = 45mA RMS which is still OK.
Each transformer can provide 1.85A RMS. In this circuit, this is 1.85A from + to ground and 1.85A from - to ground. The loudspeakers are rated 50W, 8Ohm each. Even when the whole current is supplied to each speaker, this will see 1.85A RMS from + to ground and 1.85A RMS from - to ground. This makes 2 * 1.85 = 3.7A RMS. Thus the overall maximum power a speaker can see is 3.7^2 * 8 = 109.52W RMS. In order for this to happen, the voltage at the speaker has to be 29.6V RMS. Each of the transformers can provide 18V RMS. Thus the two transformers can provide 36V RMS.
The voltage after the bridge is ( 18 / 0.707 - 1.4 ) * 0.707 = 17V. Thus the voltage between the + and the - of the power supply is 34V.
The common collectors will repeat the voltage displayed at their input (when they can). The operational amplifiers are supplied with 34V and can theoretically swing their outputs from negative rail to positive rail minus 1.5V. This is from - 17V to + 15.5V. To keep the symetry, the maximum normal working voltage can be - 15.5 to + 15.5. This gives an RMS of 15.5 * 0.707 = 10.96V RMS for a pure sine wave. In the worst case, the operational amplifier can display negative saturation only, which is - 17V DC. A fully open transistor will consume Vce of 0.3V, in some cases more. Assume 0 consumption from the transistor to work the worst case out. Thus the speaker will see <= 17V RMS. At 17V, the speaker will get 2.125A which gives 36.125W which is below the maximum power of each of the speakers which is 50W. Thus the speakers will not be damaged by the amplifier.
HOWEVER, I think the best practice is to assume, somehow, caused by a damage to the circuitry, the whole power of the output is applied to the speaker, this is 36V at 1.85A which is 67W. This is dangerous for the speaker. I believe the speaker can take so much but is not rated for. 67W is only 100 * ( 67 - 50 ) / 50 = 34% higher then 50W. Usually, any equipment should be able to witstand at least 1/3 higher than the rated.
ONLY NON DARLINGTON COMMON COLLECTORS ARE DISCUSED BELOW. THE DIFFERENCE WILL BE NOTED AT THE END.
A transistor will consume 0 power when fully open and fully closed. ( Vce when fully open ignored. ) As the voltage Vce decreases, the current Ice increases. In the middle, the power consumption will be ( Vce / 2 ) * ( Ice /2 ) = Vce * Ice / 4. The question is whether this is the maximal optimum of the function voltage multiplied by current.
Anyways, each transistor will see less than or equal to 17V and 1.85A. When not divided by 4, this is 31.45W. When divided, this is 7.8625W, 8W. Either of these are below the TIP41 / 42B ratings.
A good way to calculate the maximum power poossible to be dissipated by a transistor is to assume the very worst case of maximum voltage and maximum current of the power supply can be applied to / through a transisitor. In this case, this is 36V * 1.85A = 67.86W which is approximately the power rating of 65W of TIP41 / 42B. So, the transistors will be OK, too.
In the normal circumstances, when the amplifier output becomes positive, one of the transistors will be open to the desired extend and the other one will be fully closed. The base emitter voltage Vbe will be 0.7V and the direction will be in conducting direction of one of the base emitter junction of one of the junctions and non conducting of the other. Thus, one of the transistors will take care of half of the speaker's work, giving the full amplitude voltage of the speaker ( connected to ground ), half of the RMS voltage of the speaker and half of the RMS current through the speaker. Thus each of the transistors will take care of half of the work and half of the power of the speaker.
In non Darlington, the operational amplifier output will swing between - ( 0.7V + uout) to + ( 0.7 + uout), where uout is the amplitude of the output. In Darlinton, the BE junction of the two transistors are in series, thus the "common" BE voltage will be 1.4V. Thus, the operational amplifier will swing from - ( 1.4 + uout ) to + ( 1.4 + uout ). However, the OA output can only swing from - 15.5 to + 15.5 in normal operations. Therefore, the loudspeaker voltage can swing from - 14.1V to + 14.1V. Thus, RMS of 14.1 * 0.707 = 10V in pure sine. The worst case is fully distorted ( rectangular / square ) voltage with RMS of 14.1. Even worse case is negative rail and positive rail minus 1.5V (TL084 can reach 1.5V below positive rail ONLY), - 17 to 15.5 with duty cycle 50% which gives ( 17 + 15.5 ) / 2 = 16.25V RMS. Of course, the very worst case is: 100% duty cycle for the negative rail or 17V DC which brings power of 17 ^ 2 / 8 = 36.125W. In normal work (symetrical), the maximum voltage the output would see is 14.1V square / rectangular and the maximum normal working power is 14.1 ^ 2 / 8 = 25W which is how an amplifier is supposed to be rated. In pure sine, the maximum normal working output is ( 14.1 * 0.707 ) ^ 2 / 8 = 100 / 8 = 12.5W. This is a parameter good to be displayed.
I have been making the mistake saying the output of the OA would swing - 0.7V to + 0.7V in non Darlington. Must be read - 0.7V to + 0.7V higher / lower than the output voltage.
In order to avoid or minimise the mistakes, this circuit has to be looked at as a single transistor non push pulled circuit and only one wave assumed.
To Do:
1. Put the capacitor decoupled output of the pre amplifiers
2. Put an extra resistor and a switch at the input to provide for a possibility to put a low value resistor for microphones in case so desired.
3. The best, use a multi switch ( rotary ) for the input. See whether there are any except the fat 18 position rotary switches. Arrange the switch as follows: strait connection to the source, high value resistor, low value resistor, ground ( although ground can be provided by the input jack sockets unless they are guitar ones ( 1 / 4 " )
4. Consider a possibility for a potentiometer at the input for those who insist on getting exact different resistance for a specific microphone.
5. Consider current to voltage convertors as input preamplifiers. Non inverting amplifier without R1. R1 can be switchable for voltage outputs. Or the whole input circuitry.
Schematics
All resistors are 5%, 1/4W. All capacitors are >=18V.
Taking the TL084 in pure form would give THD of 0.03% as far as I remember. The specifications are at ti.com
The rest is in other posts I have made or I am to make.
Ideal operational amplifier is an abstraction which is used for analysis purposes but the real operational amplifier is very close to the ideal except the capacitive loads.
Complex mathematical analysis is there but they do not have anything to do with electronics. These can be used elsewhere as well as in electronics but these are not part thereof. They ARE helpful, no doubt. And they are not dangerous. Spice, however, may be dangerous. Spice may lead the designer to make logical mistakes. Of course, being similar to building a circuit, Spice can show problems too. I believe the better way is without rather than with. Imagine you are Spice. You can pass through the schematic just as good with exception of some physical parameters as noise for which you can only make predictions.
Electronics cannot be complicated because there is nothing to make electronics complicated. Again, complex mathematical as well as physics analysis are not part of electronics but, rather, a tool which may be used. Not necessary in most cases. An example of logical and physical mathematical analysis may be analogue computing. General purpose electronics does not get significantly improved or made better by the use of mathematics or physiscs. Just simple rotations of a few basic principles and nothing else. Very much alike the game Black Jack. Bridge may be complicated but Black Jack is not and cannot be. There is nothing to bring complications.
The rest is in other posts I have made or I am to make.
Ideal operational amplifier is an abstraction which is used for analysis purposes but the real operational amplifier is very close to the ideal except the capacitive loads.
Complex mathematical analysis is there but they do not have anything to do with electronics. These can be used elsewhere as well as in electronics but these are not part thereof. They ARE helpful, no doubt. And they are not dangerous. Spice, however, may be dangerous. Spice may lead the designer to make logical mistakes. Of course, being similar to building a circuit, Spice can show problems too. I believe the better way is without rather than with. Imagine you are Spice. You can pass through the schematic just as good with exception of some physical parameters as noise for which you can only make predictions.
Electronics cannot be complicated because there is nothing to make electronics complicated. Again, complex mathematical as well as physics analysis are not part of electronics but, rather, a tool which may be used. Not necessary in most cases. An example of logical and physical mathematical analysis may be analogue computing. General purpose electronics does not get significantly improved or made better by the use of mathematics or physiscs. Just simple rotations of a few basic principles and nothing else. Very much alike the game Black Jack. Bridge may be complicated but Black Jack is not and cannot be. There is nothing to bring complications.
What you say is true. The operational amplifier cannot make the 0.7V in forward direction more than 0.7V. Thus the closed transistor will see 0.7V in oposite direction. Will this lead to crossover? I cannot tell you for sure. I have seen many people using this and claiming 0.7 in the oposite direction is good enough to fully close the transistor being 1.4V less than what is necessary to open the transistor.
I have been a fan over the years of puting zeners, diodes or resistors in sequence to the base for more reliable closing. However, this will make the AB output loose another 0.7V. In case of Darlinton, this is 1.4V. Hence, I have decided not to put these. However, whoever wants may do so. A 3.3V zeners will make a non Darlington AB transistors have 4V in the oposite direction which will lead to total closing down not counting the leakage.
Obviously, a diode would have another advantage: current can't go in the oposite direction, thus, there isn't any way for the current to be open, the same as the BE junction. The leakage is there, though. The diode and the BE junction are in series.
Also, cross talk between the transistors is not a problem. THE TRANSISTORS ARE BEFORE THE FEEDBACK AND THE FEEDBACK WILL MAKE SURE WHATEVER IS AT THE INPUT IS AT THE OUTPUT. Even not very well closed transistor would not make a difference. Just current flies from + to - and the two transistors make a voltage divider very close to 1 thus the output of the operational amplifier IC may need to pump a negligibly tiny theoretical amount more which may be ignored.
Please, note the difference between AB BEFORE THE FEEDBACK and AB after.
The problem with the crosstalk between the two channels may seem to be theoretically a bit more because the current going from + to - or vice versa through the "not fully closed" transistor will go through the capacitors of the power supply which are not ideal and have some parasitic resistance. The power supply is not ideal and has some output resistance too. Thus cross talk travels between the channels through the power supply. The same happens with the current through a given speaker as far as I can imagine. The current through the not fully closed transistor is negligible as compared to the speaker current.
Most sources would use the transistors directly. I have spent 1 minute but I cannot find any and I do not want to spend more.
I agree with you, however, to close reliebly a transistor which is not used is very good.
I have been a fan over the years of puting zeners, diodes or resistors in sequence to the base for more reliable closing. However, this will make the AB output loose another 0.7V. In case of Darlinton, this is 1.4V. Hence, I have decided not to put these. However, whoever wants may do so. A 3.3V zeners will make a non Darlington AB transistors have 4V in the oposite direction which will lead to total closing down not counting the leakage.
Obviously, a diode would have another advantage: current can't go in the oposite direction, thus, there isn't any way for the current to be open, the same as the BE junction. The leakage is there, though. The diode and the BE junction are in series.
Also, cross talk between the transistors is not a problem. THE TRANSISTORS ARE BEFORE THE FEEDBACK AND THE FEEDBACK WILL MAKE SURE WHATEVER IS AT THE INPUT IS AT THE OUTPUT. Even not very well closed transistor would not make a difference. Just current flies from + to - and the two transistors make a voltage divider very close to 1 thus the output of the operational amplifier IC may need to pump a negligibly tiny theoretical amount more which may be ignored.
Please, note the difference between AB BEFORE THE FEEDBACK and AB after.
The problem with the crosstalk between the two channels may seem to be theoretically a bit more because the current going from + to - or vice versa through the "not fully closed" transistor will go through the capacitors of the power supply which are not ideal and have some parasitic resistance. The power supply is not ideal and has some output resistance too. Thus cross talk travels between the channels through the power supply. The same happens with the current through a given speaker as far as I can imagine. The current through the not fully closed transistor is negligible as compared to the speaker current.
Most sources would use the transistors directly. I have spent 1 minute but I cannot find any and I do not want to spend more.
I agree with you, however, to close reliebly a transistor which is not used is very good.
a couple of things required for amplifier design are DC conditions and AC conditions. the output stage in the schematic posted has no DC biasing, it might run from the AC swing from the opamp making it class C, which is undesirable in audio due to the non linear mixing action. you should try using a electronics design program.
Output stage
The output stage is terrible.
The feed back will NOT make it good.
You were told so and you did not listen.
I do recommend you use LTspice to simulate your output stage.
You will see how terrible it is.
It will prove to you, that negative feedback doesn't eliminate the crossover trouble.
The output stage is terrible.
The feed back will NOT make it good.
You were told so and you did not listen.
I do recommend you use LTspice to simulate your output stage.
You will see how terrible it is.
It will prove to you, that negative feedback doesn't eliminate the crossover trouble.
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The feedback does definitely make everything better everywhere. ONLY WHEN physically possible.
I will not run Spice even in case the company pays to run their software. However, PLEASE EXPLAIN what problem you see and I will admit this as being a problem with a great pleasure because I would not have to type so much anymore. I would also may try to correct this.
Here is something in regards to your slogan. Please take this as a joke not as an insult" "The feedback does not care what temperature is what. The feedback just controls all temperatures!"
I will not run Spice even in case the company pays to run their software. However, PLEASE EXPLAIN what problem you see and I will admit this as being a problem with a great pleasure because I would not have to type so much anymore. I would also may try to correct this.
Here is something in regards to your slogan. Please take this as a joke not as an insult" "The feedback does not care what temperature is what. The feedback just controls all temperatures!"
DC biasing is provided by the operational amplifier. The transistors are before the feedback.
The output would have distortion without the operational amplifier and the feedback. With the feedback, the distortion will be taken care of. The voltage at the output will be the same shape as the voltage of the input just amplified. In case of a buffer, the output voltage will be the same as the input voltage.
The output would have distortion without the operational amplifier and the feedback. With the feedback, the distortion will be taken care of. The voltage at the output will be the same shape as the voltage of the input just amplified. In case of a buffer, the output voltage will be the same as the input voltage.
Agreed, but there is a limit to how much better it can make it.
In an opamp gain stage, the feedback factor is typically about 100 in the upper treble, so we can expect that distortion nasties in the upper treble will be reduced about one hundred-fold by the feedback.
With your output stage, if there is no feedback, or with feedback taken from before the output transistors, distortion will be very bad. When the output is only a couple of volts for normal listening levels, distortion can easily be 50% or more.
With feedback added, distortion is greatly reduced, but you're still left with perhaps 0.5% or so distortion in the treble, which is likely to sound nasty.
There's another problem too. When the signal passes through zero, the voltage at the output of the opamp is required to jump instantly between -1.4V and +1.4V. Unfortunately this is not possible due to the slew rate limitation of the opamp, so at each zero crossing there is a gap of perhaps 1uS or so during which time nothing is happening at the amp's output and the feedback is powerless to correct anything.
Theoretically, the second point is true. The operational amplifier is not unlimited in speed. With the post of the Simple Amplifier which I have made t, however, the difference of a bit more than + / - 1.4 V is very tiny as compared to the supply voltage of + - 18V or even + - 12V. Thus, this jump wiill happen increadibly fast and will not have any effect. With this schematic ( common collectors with Darlingtons ), the operational amplifiers output would go from ( - output - 1.4V) to ( output + 1.4V ). This makes your point stronger. I keep making the mistake with - 1.4V to + 1.4V over and over and over.
For push pulls without an operational amplifiers, what you say is true.
For this schematic with a fast amplifier and LOW GAIN, the jump may as well take one or a few nanoseconds. Faster amplifiers can probably make this delay even more negligible. Compare this with not so accurate digitisation frequency ( crystals are not ideal either, although, I must admit, pretty close ) or with the loss of information caused by digitisation. Compare this also with the moving of the zero crossing left or right because of noise, even being only the internal noise of solid state components which becomes higher with the higher temperature of the drivers.
This jump is the only reason for distortions and non linearity.
However, you are right I should have written the zero crossing point up. I neglected so because I ignored the negligible value. After all, this is the biggest problem with push pulls and this is why the operational amplifier is there.
Another problem with push pulls is the difference in parameters of the transistors. This problem does not exist with operational amplifier control. Obviously, being not ideal, the operational amplifier will not be able to fully equalise the negative and positive wave. The difference will be negligible.
Another problem with transistors is the nonlinearity in high span range which is also covered by the operational amplifier control mainly when this works at low range. At high range, the operational amplifier will have non linearity typically displaying 0.03%.
I do not seem to agree there is another reason for distortions with push pulls as far as I can find now. I do not seem to agree the distortions would have such a bigger value. As far as the quantities go, one has to build the circuit and compare against the rest under normal working circumstances.
I think your reply was the best so far. I do not seem to agree with the first point as I have been saying many times but the second point is something which no one can disagree with. The problem is: I should have mentioned this.
For push pulls without an operational amplifiers, what you say is true.
For this schematic with a fast amplifier and LOW GAIN, the jump may as well take one or a few nanoseconds. Faster amplifiers can probably make this delay even more negligible. Compare this with not so accurate digitisation frequency ( crystals are not ideal either, although, I must admit, pretty close ) or with the loss of information caused by digitisation. Compare this also with the moving of the zero crossing left or right because of noise, even being only the internal noise of solid state components which becomes higher with the higher temperature of the drivers.
This jump is the only reason for distortions and non linearity.
However, you are right I should have written the zero crossing point up. I neglected so because I ignored the negligible value. After all, this is the biggest problem with push pulls and this is why the operational amplifier is there.
Another problem with push pulls is the difference in parameters of the transistors. This problem does not exist with operational amplifier control. Obviously, being not ideal, the operational amplifier will not be able to fully equalise the negative and positive wave. The difference will be negligible.
Another problem with transistors is the nonlinearity in high span range which is also covered by the operational amplifier control mainly when this works at low range. At high range, the operational amplifier will have non linearity typically displaying 0.03%.
I do not seem to agree there is another reason for distortions with push pulls as far as I can find now. I do not seem to agree the distortions would have such a bigger value. As far as the quantities go, one has to build the circuit and compare against the rest under normal working circumstances.
I think your reply was the best so far. I do not seem to agree with the first point as I have been saying many times but the second point is something which no one can disagree with. The problem is: I should have mentioned this.
Ask yourself this question.
Why does nobody else use the method you are suggesting? (using a driving opamp to try to also bias the output devices) I do not know for sure. Perhaps you are the first person ever to think up this idea. Maybe no one ever tried it before and it works fine?
Whatever your objection to 100% free simulators might be, I can not imagine.
They are just a FREE tool to add to all other tools.
That is like saying "I will never use a wrench no matter what, even if you give me one for free". Ok?
It's either that or you have to build a prototype.
Have you built any of your designs as prototypes or finished units to date?
Many who do find that things often do not work exactly as theory or they expected them to.
Regards,
_-_-bear
Why does nobody else use the method you are suggesting? (using a driving opamp to try to also bias the output devices) I do not know for sure. Perhaps you are the first person ever to think up this idea. Maybe no one ever tried it before and it works fine?
Whatever your objection to 100% free simulators might be, I can not imagine.
They are just a FREE tool to add to all other tools.
That is like saying "I will never use a wrench no matter what, even if you give me one for free". Ok?
It's either that or you have to build a prototype.
Have you built any of your designs as prototypes or finished units to date?
Many who do find that things often do not work exactly as theory or they expected them to.
Regards,
_-_-bear
Here is what happens:
The input voltage adjusts the output voltage to be the same just amplified. This is done by the operational amplifier driving the push pull common collectors. The voltage at the output of the operational amplifier is 1.4V higher / lower than the voltage of the output for the positive / negative wave. As the input voltage goes from high to low, so does the output. When the input voltage is very close to 0, the input voltage requires the output voltage to also go close to zero. This will happen to the output voltage of the circuit but not to the output voltage of the operational amplifier which will remain higher than the voltage necessary for the transistors to stay open which is around 1.4V. This situation stays on until the input voltage goes to a bit lower than 0. Then the operational amplifier has to close one of the Darlingtons and open the other and adjust the output voltage to a value a bit lower than zero. So, the operational amplifier must quickly go from around 1.4V to around -1.4V. Then, as the input voltage goes lower, the operational amplifier output will go lower too and will be approximately 1.4V lower than what is necessary to equalise the divided by the feedback resistors output of the circuit to the input voltage.
During the “jump” of the operational amplifier output from around 1.4V to around -1.4V, the two transistors are closed and no output is displayed. However, the transistors are not perfect and have some inertia caused by the 5pF BE junction capacitor. So, the transistors will retain the around zero value for a while. The higher the current through the transistors the lower the delay the faster the switch.
The problems which have caused so many comments are related to the past. In the past, push pulls were used in transistors in order to boost the efficiency. These were not connected with an overall ( general ) feedback and were not run by operational amplifiers. Then, the first operational amplifiers were very slow, although they have improved the performance to a usable level. These days, the operational amplifiers are so fast, I would not be suprised they switch faster than the transistors.
The lower the closed loop gain the faster the switch. The output will not be divided before being presented to the input. A tiny change in the output would make a bigger change at the input subtractor ( differential input ). This is also why the operational amplifiers are faster at unity gain.
The higher the open loop gain the faster the switch.
The faster the operational amplifier and the faster the transistors the lower the imperfect effect. A major concern has been the operational amplifier speed and not the speed of the transistors. Therefore, one can have a close look at the specifications. Even a simple, general purpose operational amplifier as TL084 would have a slew rate of: 13 V/µs typical, which would give 200ns to the operational amplifier to jump. Fast operational amplifiers could go faster in the nanosecond range. This is nothing as compared to the other problems which exist with electronic circuits.
Again: the operational amplifier will make the output be the same as the input, just amplified, as long as this is physically possible. With this schematic, to do so is physically possible. And impossible without a problem. The problem appears when the input crosses 0 volts. The problem will make a very tiny voltage which is supposed to be displayed at the output to look 0. The faster the frequency the less tiny this voltage is ( the more the input would go before the output is on ( reacts ) ). HOWEVER, SOUND SIGNALS ARE INCREDIBLY SLOW SIGNALS AND THE VERY MAXIMAL FREQUENCY IS LESS THAN 30KHz.
Compare the problem with the switch with the digitisation which also does not display exactly the same voltage as well as does not get the zero exactly perfectly due to digitisation of the period as well as digitisation of the level ( voltage ). Yet, digital systems are the systems with the best sound.
Anyways, whoever wants to do calculus, you may wish to calculate how much a pure sine voltage changes after the 0 point when the frequency is 25KHz for 200ns.
Again, your concerns are concerns for push pull transistors without operational amplifier and a common feedback.
The input voltage adjusts the output voltage to be the same just amplified. This is done by the operational amplifier driving the push pull common collectors. The voltage at the output of the operational amplifier is 1.4V higher / lower than the voltage of the output for the positive / negative wave. As the input voltage goes from high to low, so does the output. When the input voltage is very close to 0, the input voltage requires the output voltage to also go close to zero. This will happen to the output voltage of the circuit but not to the output voltage of the operational amplifier which will remain higher than the voltage necessary for the transistors to stay open which is around 1.4V. This situation stays on until the input voltage goes to a bit lower than 0. Then the operational amplifier has to close one of the Darlingtons and open the other and adjust the output voltage to a value a bit lower than zero. So, the operational amplifier must quickly go from around 1.4V to around -1.4V. Then, as the input voltage goes lower, the operational amplifier output will go lower too and will be approximately 1.4V lower than what is necessary to equalise the divided by the feedback resistors output of the circuit to the input voltage.
During the “jump” of the operational amplifier output from around 1.4V to around -1.4V, the two transistors are closed and no output is displayed. However, the transistors are not perfect and have some inertia caused by the 5pF BE junction capacitor. So, the transistors will retain the around zero value for a while. The higher the current through the transistors the lower the delay the faster the switch.
The problems which have caused so many comments are related to the past. In the past, push pulls were used in transistors in order to boost the efficiency. These were not connected with an overall ( general ) feedback and were not run by operational amplifiers. Then, the first operational amplifiers were very slow, although they have improved the performance to a usable level. These days, the operational amplifiers are so fast, I would not be suprised they switch faster than the transistors.
The lower the closed loop gain the faster the switch. The output will not be divided before being presented to the input. A tiny change in the output would make a bigger change at the input subtractor ( differential input ). This is also why the operational amplifiers are faster at unity gain.
The higher the open loop gain the faster the switch.
The faster the operational amplifier and the faster the transistors the lower the imperfect effect. A major concern has been the operational amplifier speed and not the speed of the transistors. Therefore, one can have a close look at the specifications. Even a simple, general purpose operational amplifier as TL084 would have a slew rate of: 13 V/µs typical, which would give 200ns to the operational amplifier to jump. Fast operational amplifiers could go faster in the nanosecond range. This is nothing as compared to the other problems which exist with electronic circuits.
Again: the operational amplifier will make the output be the same as the input, just amplified, as long as this is physically possible. With this schematic, to do so is physically possible. And impossible without a problem. The problem appears when the input crosses 0 volts. The problem will make a very tiny voltage which is supposed to be displayed at the output to look 0. The faster the frequency the less tiny this voltage is ( the more the input would go before the output is on ( reacts ) ). HOWEVER, SOUND SIGNALS ARE INCREDIBLY SLOW SIGNALS AND THE VERY MAXIMAL FREQUENCY IS LESS THAN 30KHz.
Compare the problem with the switch with the digitisation which also does not display exactly the same voltage as well as does not get the zero exactly perfectly due to digitisation of the period as well as digitisation of the level ( voltage ). Yet, digital systems are the systems with the best sound.
Anyways, whoever wants to do calculus, you may wish to calculate how much a pure sine voltage changes after the 0 point when the frequency is 25KHz for 200ns.
Again, your concerns are concerns for push pull transistors without operational amplifier and a common feedback.
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