I have made a couple of simple preamplifiers, described in the document :
Preamplifiers - Google Drive
Preamplifiers - Google Drive
One observation: re: "The two of the preamplifiers are in Aluminium enclosures. The simpler one, the guitar one, is in an 3mm thick enclosure, which is supposed to reduce the electromagnetic noise."
Increased thickness will give more attenuation but it a severe case of diminishing returns once past the 'thick foil' stage and becomes more an issue of sturdiness and fabrication / drilling etc. Also bear in mind that Aluminium will give little protection against low frequency predominantly H-field noise like you get from mains transformers etc. To do anything significant there you need a ferrous - eg steel enclosure. Ideally you'd have mu-metal but that's not practicable or affordable !
Increased thickness will give more attenuation but it a severe case of diminishing returns once past the 'thick foil' stage and becomes more an issue of sturdiness and fabrication / drilling etc. Also bear in mind that Aluminium will give little protection against low frequency predominantly H-field noise like you get from mains transformers etc. To do anything significant there you need a ferrous - eg steel enclosure. Ideally you'd have mu-metal but that's not practicable or affordable !
Yes, for magnetic fields, ferrous metals may be preferable. For electrical fields and electromagnetic fields with strong electrical part, conductive metals are preferable.
Copper is the best of the inexpensive materials, but, Copper enclosures may be difficult to find. Aluminium enclosures are, somewhat, more available and unfairly expensive as Aluminium is extremely inexpensive.
Yes, you are right, Looks like a two metal enclosure, Steel and Aluminium, may be a good idea where available. Also, when Aluminium touches Steel, Steel does not rust. The can be press fit tightly, so, everywhere, Aluminium touches Steel and then bolted. However, even when Aluminium does not touch Steel everywhere, but, instead, in close proximity, Steel does not rust. I think, this is explained with the opposite potentials of Steel and Aluminium.
When not available, I always prefer conductive metal, such as Copper and Aluminium, than Ferrous. I am not sure whether I am right or wrong.
True, commercial companies use Steel, but, they, probably, choose so in order to reduce their costs.
Here is what Wikipedia says :
Electromagnetic shielding - Wikipedia
:
"
For example, electrically dominant waves are reflected by highly conductive metals like copper, silver, and brass, while magnetically dominant waves are absorbed/suppressed by a less conductive metal such as steel or stainless steel.
"
Faraday cage - Wikipedia
Copper is the best of the inexpensive materials, but, Copper enclosures may be difficult to find. Aluminium enclosures are, somewhat, more available and unfairly expensive as Aluminium is extremely inexpensive.
Yes, you are right, Looks like a two metal enclosure, Steel and Aluminium, may be a good idea where available. Also, when Aluminium touches Steel, Steel does not rust. The can be press fit tightly, so, everywhere, Aluminium touches Steel and then bolted. However, even when Aluminium does not touch Steel everywhere, but, instead, in close proximity, Steel does not rust. I think, this is explained with the opposite potentials of Steel and Aluminium.
When not available, I always prefer conductive metal, such as Copper and Aluminium, than Ferrous. I am not sure whether I am right or wrong.
True, commercial companies use Steel, but, they, probably, choose so in order to reduce their costs.
Here is what Wikipedia says :
Electromagnetic shielding - Wikipedia
:
"
For example, electrically dominant waves are reflected by highly conductive metals like copper, silver, and brass, while magnetically dominant waves are absorbed/suppressed by a less conductive metal such as steel or stainless steel.
"
Faraday cage - Wikipedia
I think, the best guitar preamplifier can be made by this arrangement :
1. Instrumentation amplifier made by two input buffers, made by JFET input amplifiers and the third amplifier of the instrumentation amplifier can be with bipolar inputs to reduce the noise as well as every consequent amplifier. One of the input JFET buffers is connected to the guitar output, the other to the guitar output's ground.
2. A second order Sallen Key Filter.
3. An amplifier. Can be inverting for customer friendliness, but, non inverting may be preferable.
4. Another Sallen Key Filter.
5. A separate output buffer.
Whoever wants to put a standard, 1M resistor with a switch between the inputs is welcome. Some people say their coils and humbuckers are designed for 1M. I think the higher the input impedance the better for the whole frequency range.
The Sallen Key filters will provide an overall 4th order filter. They must be so calculated to provide - 3dB at 20Hz and 20KHz to match the requirements of HiFi frequency range.
Whoever wants to cut the lowest frequency at > 60Hz is welcome. Standard Italian tuning has the lowest frequency of open thick E at 82.41Hz. Very few people play with the thickest string tuned to D ( 73.42Hz ).
The problem is some people prefer to change tuning than to change the guitar positions.
Anyway, the idea to cut at > 60Hz can be made optional. The idea helps reduce the 60Hz ( 50Hz ) noise, but, not the rectified 120Hz ( 100Hz ) noise.
The idea of an instrumentation amplifier configuration input is to reduce the noises on the guitar line and ground, which noises are with the same phase.
In addition, the input impedance will be huge.
1. Instrumentation amplifier made by two input buffers, made by JFET input amplifiers and the third amplifier of the instrumentation amplifier can be with bipolar inputs to reduce the noise as well as every consequent amplifier. One of the input JFET buffers is connected to the guitar output, the other to the guitar output's ground.
2. A second order Sallen Key Filter.
3. An amplifier. Can be inverting for customer friendliness, but, non inverting may be preferable.
4. Another Sallen Key Filter.
5. A separate output buffer.
Whoever wants to put a standard, 1M resistor with a switch between the inputs is welcome. Some people say their coils and humbuckers are designed for 1M. I think the higher the input impedance the better for the whole frequency range.
The Sallen Key filters will provide an overall 4th order filter. They must be so calculated to provide - 3dB at 20Hz and 20KHz to match the requirements of HiFi frequency range.
Whoever wants to cut the lowest frequency at > 60Hz is welcome. Standard Italian tuning has the lowest frequency of open thick E at 82.41Hz. Very few people play with the thickest string tuned to D ( 73.42Hz ).
The problem is some people prefer to change tuning than to change the guitar positions.
Anyway, the idea to cut at > 60Hz can be made optional. The idea helps reduce the 60Hz ( 50Hz ) noise, but, not the rectified 120Hz ( 100Hz ) noise.
The idea of an instrumentation amplifier configuration input is to reduce the noises on the guitar line and ground, which noises are with the same phase.
In addition, the input impedance will be huge.
A document, called Errata.doc has been published here : Errata - Google Drive
The document correct errors I may have made in various projects I have worked on.
The document is to be updated.
Please, report all errors and problems.
The document correct errors I may have made in various projects I have worked on.
The document is to be updated.
Please, report all errors and problems.
I have written a document on the possible applications of the instrumentation amplifier configuration for audio. The document is called " ADOD.doc " and is in the same folder as the original document of this post : Preamplifiers - Google Drive
Probably best to look at a lot of guitar amp and effects pedal schematics. The devices most commonly used by good studio players may be a good place to start. Opamps are not generally used unless they are needed for particular effect, say, for example, in a tube-screamer type circuit. Instrumentation amps are rare. Why? Because people who listen to the resulting guitar sound often find such circuits sterile and lifeless sounding. Maybe better to put up with a little hum.
Have any musicians actually used your preamp? It doesn't make sense to me as being actually useful.
You mentioned blowing up tantulum capacitors. Tantulum capacitors always, always, always need surge current limited with a resistor or else they will blow up. This I think is why they've fallen out of favor.
Also, your circuit doesn't have basic protections. Your presentation is very good, but your ideas need work. (I'm exactly the opposite- excellent circuits but horrible documentation.)
You mentioned blowing up tantulum capacitors. Tantulum capacitors always, always, always need surge current limited with a resistor or else they will blow up. This I think is why they've fallen out of favor.
Also, your circuit doesn't have basic protections. Your presentation is very good, but your ideas need work. (I'm exactly the opposite- excellent circuits but horrible documentation.)
why use 4 opamps when 2 would do the same thing?
It will sound dull when you only cut the treble, you need gain too. same for the bass.
Why +/-15V rails when all pedals have only a 9V battery
The power amp will blow up if you plug in the guitar, since there is no input bias resistor and the input will slowly ramp up to the rail.
The cable will have 500pF+ capacity, so input capacitance doesn't matter much.
The pick-up will sound the same with 1M or 1G jnput impedance. the cable has already only 32k impedance at 10kHz.
It will sound dull when you only cut the treble, you need gain too. same for the bass.
Why +/-15V rails when all pedals have only a 9V battery
The power amp will blow up if you plug in the guitar, since there is no input bias resistor and the input will slowly ramp up to the rail.
The cable will have 500pF+ capacity, so input capacitance doesn't matter much.
The pick-up will sound the same with 1M or 1G jnput impedance. the cable has already only 32k impedance at 10kHz.
Operational Amplifiers are the best for any case. ( Some insane frequencies may need pure transistors. ) Audiophiles are idiots who do not know what they say, thus, how something sounds is not up to them to say, but, up to a measurement equipment.
Therefore, I do not care what they say and you should not too. The only sound is a pure sound with all of the frequencies and zero distortion. Of course, zero noise is, probably, the only thing they got right.
You are totally wrong. Read the previous reply to understand the stupidity of audiophiles and musicians and the only way to make a circuit ( all frequencies, zero distortion, zero noise ). Thus, the circuits I make are excellent and your are not ( you said they do not use these principles ). I make mistakes, however, thus, any problem may be caused by a mistake and because of the idea.
No, Tantalum capacitors do NOT need a resistor and they can take surge currents OK. Exception : some Chinese, 25V tantalums ( usually, 10uF ). The only thing most Chinese Tantalum capacitors need is voltage derating. Non Chinese Tantalums are OK.
Tantalums must be used, because of their lower ESR and ESL, compared to the electrolitics. Rule of thumb : always use the bigger tantalum possible ( price too ) in parallel to every electrolytic.
Of course, use a lot of Ceramics in parallel too. They are with the lowest ESR and ESL. Must be Japanese, though. TDK, NTE, etcetera. 1uF or around may have the lowest ESR of a line. The higher the voltage, the lower the ESR too, thus, 100V may be better than 50V. X7R are, usually, the line with the lowest ESR.
Well, just the fact you listen to musicians means your circuits are very badly designed. However, I am sure they would be the best when you stop listening to audiophiles, musicians and other alchemists. They talk with their ***** and not their brains. Especially on sound.
However, the REAL musicians, the classicals, are slightly different. Most of them would prefer pure sound.
As far as the alchemists are concerned, there is a bass and treble filter for them.
The biggest stupidity I have heard is " vinyl sounds better ". Vinyl sounds somewhere between a belch and a flatulence.
1. I do not know what amplifiers you talk of, but, all have a purpose.
2. Again, I do not understand what you talk of, but, there is a bass filter potentiometer and a treble filter potentiometer. These must be to the maximum ( or minimum ) to allow full sound without filtering neither the bass nor the treble, i. e., pure sound.
3. Other people make crap. Dual power supply is better than single ( with or without a virtual ground split ). 9V is garbage.
4. 30V ( + - 15V ) is the best voltage for operational amplifiers. Higher OK ( the amplifier must be rated for higher, most of them are ). Lower : bad parameters.
5. The amplifier must be able to take ( + - 15V ) or the preamplifier must not be cranked so high. However, much better is to have a power amplifier which can handle these. Most of them can. Most of them are supplied with the same or higher voltage.
6. There must not be any input resistor. Guitars need as high input resistor as possible. 1M is too low. Not only the signal is lost, but, also, the pickups will need to supply high current and will drag the strings. Teraohms are very welcome.
7. The lower the cable capacitance the better. Again, the cable capacitance must be such, so, at 20 to 40KHz, the impedance must be super high. Again, teraohms are very welcome. Usually, the shorter the cable the better and the capacitance is ignorable. Must be << 0.5pF. The amplifier's inputs can have around 5pF.
8. Instrumentation amplifier gives the best input : 1. Huge input impedance, usually, defined by the input impedance of the amplifier. 2. Lowest noise : one of the amplifiers can have the Ground as input, the other, the signal. Then, the noise with the same phase on signal and ground ( the typical noise ) is subtracted.
I am in a process of making another preamplifier and a full distortion ( a. k. a., fuzz ). These are the only thing I use and need. So, here is the topology of the preamplifier :
All amplifiers, audio.
The goal : Pure sound : whatever the guitar outputs ( between 20Hz and 20KHz ) must be displayed at the output, only, amplified. No noise. Audio power supply ( + - 15V ). Tons of different capacitors. Every amplifier IC : power supply capacitors.
The preamplifier can be used as such or a 100% distortion ( pure rectangular wave, pure fuzz ) can be added. Although overdrive is easy to add, this is not necessary. Most guitar amplifiers have overdrives, but, I do not care, because, I use, only, what people call fuzz, i. e., only 100% rectangular wave distortion with a Schmitt trigger comparator. Of course, for noise, the Schmitt trigger level must be adjustable between 0 and, say 1V or more.
And I do not care what other people say, because, I either want to have a pure guitar or 100% distorted, rectangular fuzz. Nothing in between.
Tone control can be added. Initially, I thought of putting something there. Two passive filters with a buffer thereafter. Surrounded by filters as mentioned. But, now, I do not want them, because, I will never use them. Again, either pure or fully distorted, nothing in between.
I have a commercial distortion, FAB Metal by Danelectro. Of course, I only use this at full distortion setting.
And I do NOT care what they used in the 60's, because they did not have amplifier IC's or for whatever, stupid reason.
Some people say blues requires an overdrive and not a distortion. Tough. Even blues sounds much better with 100% fuzz. They, simply, did not have those back then, otherwise, they would have used them.
- An instrumentation amplifier with two JFET buffers and a subtractor. The overall gain is - 1.
- Then a filter. Preferably, a single order band through. Additional second order Sallen Key, Basel OK.
- Then two gain amplifiers with a dual potentiometer and a gain between 1 and 30 to 40 each, Combined gain of 1000 and more. Two dual potentiometers, course and fine OK.
- Then, another filter as discussed.
- Then a buffer.
All amplifiers, audio.
The goal : Pure sound : whatever the guitar outputs ( between 20Hz and 20KHz ) must be displayed at the output, only, amplified. No noise. Audio power supply ( + - 15V ). Tons of different capacitors. Every amplifier IC : power supply capacitors.
The preamplifier can be used as such or a 100% distortion ( pure rectangular wave, pure fuzz ) can be added. Although overdrive is easy to add, this is not necessary. Most guitar amplifiers have overdrives, but, I do not care, because, I use, only, what people call fuzz, i. e., only 100% rectangular wave distortion with a Schmitt trigger comparator. Of course, for noise, the Schmitt trigger level must be adjustable between 0 and, say 1V or more.
And I do not care what other people say, because, I either want to have a pure guitar or 100% distorted, rectangular fuzz. Nothing in between.
Tone control can be added. Initially, I thought of putting something there. Two passive filters with a buffer thereafter. Surrounded by filters as mentioned. But, now, I do not want them, because, I will never use them. Again, either pure or fully distorted, nothing in between.
I have a commercial distortion, FAB Metal by Danelectro. Of course, I only use this at full distortion setting.
And I do NOT care what they used in the 60's, because they did not have amplifier IC's or for whatever, stupid reason.
Some people say blues requires an overdrive and not a distortion. Tough. Even blues sounds much better with 100% fuzz. They, simply, did not have those back then, otherwise, they would have used them.
You might want to take a look at the forum rules (like for example, Rule 1): www.diyaudio.com/community/help/terms
I know about musician's circuits and I know they're different from hi fi. I've designed custom circuits (tone stacks and distortion effects) for musicians.
And how do you know about my circuits? I guess you don't.
Finally, you can add safety features without affecting the performance of the circuit at all. A properly designed safety circuit does nothing until parameters are exceeded, and does not effect normal operation at all. There is no reason in the world to design and build circuits without safety features, except ignorance.
Tantalums were popular because they came in large values, small package, and (unlike electrolytics) low ESR and very high resonance. In the 70s they were like a magic bullet. Engineers stopped using tantalums because they blow up if too much current passes through them. They are much more delicate than electrolytics (which can blow up too).
Common film capacitors today far exceed what tantalums did or could ever do and they are far more robust. Nobody uses them any more.
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