Hi there ,
I'm Michalea and I'm a young girl who has chosen electronics as a hobby.😍
Please forgive my bad English, but Google Translator does its best 🙂😛
I've decided to do a bit with amplifiers, but I'm still having trouble understanding it.
Maybe you can help me to understand some things better and explain things more simply than it is described in the textbooks.
I bought a China LM3886 amplifier to do some testing and understanding.
I measured the circuit and have a few questions about it.
🤔
1) Why I need C1 at all when a cinch signal is already AC?
2) Are C1 and R2 a high pass? and how can I caculate it in a simple wise , which is the border frequenzes.
Which frequenzes makes sense to eliminate, e.g. under 60Hz ?
3) Why do the values for C1 vary between 1µF and 4.7µF in so many other designswith the same LM3886?
4) Why should C1 be made of foil and not electrolytic capacitor or ceramic, can you really hear the difference?
5) R3 and R4 is clear , the gain factor. But why do I need C2?
6) What is the R5 in only for? I've read some things that it would be better to have an RC (R8/C3) and RL (L1/R7) at the output so that the 3886 doesn't oscillate.
How do I find out the best values? ( see in circiut )
7) Then I saw that many have the supplement ( in red inside) , what is that for exactly? In the gain path?
8) Then I read some stuff about composite modes with an added OP, but I'll get to that later when I get the first things down.
9) What do you think is better for starting out as a youngster: KiCad oder EasyEda ?
10) I have a toroidal transformer with 2x 18V and 4x 6800µF and i got a light hum in Speakers, it almost sounds like the transformer
If I connect the earth of the 230V~ (gn/ge) to the GND of the circuit board, the humming becomes much quieter, but it doesn't go away.
11) If I have a good amplifier, what is the maximum V or mV that can be applied to output 3 of the LM3886 if the input is unused, i.e. open?
.... regards and from now on .....happy replying and writing 🙂
12 ) new on 29.01.2022 , phase shifting, see #14
I'm Michalea and I'm a young girl who has chosen electronics as a hobby.😍
Please forgive my bad English, but Google Translator does its best 🙂😛
I've decided to do a bit with amplifiers, but I'm still having trouble understanding it.
Maybe you can help me to understand some things better and explain things more simply than it is described in the textbooks.
I bought a China LM3886 amplifier to do some testing and understanding.
I measured the circuit and have a few questions about it.
🤔
1) Why I need C1 at all when a cinch signal is already AC?
2) Are C1 and R2 a high pass? and how can I caculate it in a simple wise , which is the border frequenzes.
Which frequenzes makes sense to eliminate, e.g. under 60Hz ?
3) Why do the values for C1 vary between 1µF and 4.7µF in so many other designswith the same LM3886?
4) Why should C1 be made of foil and not electrolytic capacitor or ceramic, can you really hear the difference?
5) R3 and R4 is clear , the gain factor. But why do I need C2?
6) What is the R5 in only for? I've read some things that it would be better to have an RC (R8/C3) and RL (L1/R7) at the output so that the 3886 doesn't oscillate.
How do I find out the best values? ( see in circiut )
7) Then I saw that many have the supplement ( in red inside) , what is that for exactly? In the gain path?
8) Then I read some stuff about composite modes with an added OP, but I'll get to that later when I get the first things down.
9) What do you think is better for starting out as a youngster: KiCad oder EasyEda ?
10) I have a toroidal transformer with 2x 18V and 4x 6800µF and i got a light hum in Speakers, it almost sounds like the transformer
If I connect the earth of the 230V~ (gn/ge) to the GND of the circuit board, the humming becomes much quieter, but it doesn't go away.
11) If I have a good amplifier, what is the maximum V or mV that can be applied to output 3 of the LM3886 if the input is unused, i.e. open?
.... regards and from now on .....happy replying and writing 🙂
12 ) new on 29.01.2022 , phase shifting, see #14
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to 2) : it was 6.92 Hz in 1. Order , right ? --> f_g = \frac{1}{2 \pi R C}
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Hi Micha2007
1) The input capacitor (C1) is to block any DC in the audio source. This explains it a little better:
"Cin is in series with the non-inverting input. It’s main function is to block any DC present in the audio source, while allowing AC (the audio signal) to pass. DC in the audio source needs to be blocked or it will be amplified along with the audio signal and create a high DC offset at the speakers. This distorts the audio."
3) C1 is only to block DC in the audio source, so the. capacitance doesn't have to be exact; just somewhere between 1µF and 4.7µF.
4) Who said C1 should be made of foil 🤨 . Electrolytical is usually used there.
5) R4 and C2 is the low frequency cutoff.
"The cutoff frequency of this filter should be 3 to 5 times lower than the Fc of the Cin\ Rin high pass filter at the input. If the Fc of this filter is higher than the input filter, the amplifier will pass low frequencies to the feedback loop that it can’t handle. This will create a voltage across Ciand cause DC voltage to appear at the inverting input, which will be amplified and cause distortion. Therefore, the input filter (Cin and Rin) should determine the lower bandwidth frequency of the amplifier, not the feedback loop filter (Ci and Ri)."
6) I'm not sure what R5 is. What I would put there, is a Thiele network, which consists of a resistor and an inductor.
"the Thiele network reduces oscillations caused by capacitive loads, usually due to long speaker cables. It also prevents radio frequencies picked up by the speaker wires from getting back into the amplifier’s inverting input through the feedback loop."
"The datasheet recommends a 10 Ω, 5 Watt resistor in parallel with a 0.7 µH inductor. In a stereo amplifier, there will be one Thiele network per channel. They should be located away from the amplifier’s input circuitry to prevent interference from the magnetic fields generated by the inductor."
9) I personally use EasyEDA, but I might be biased, as I have never used anything else. An added bonus is EasyEDA (PCB design), LCSC.com (electronic components) and JLCPCB.com (PCB manufacturer) are all together. So it is easy to quickly make a project and have parts and PCBs.
10) That has something to do with the ground loop. Usually to fix this, you would attach all the grounds from everything together at one point.
Hope this helps 😀
EDIT: Quotes from this very helpful website: https://www.circuitbasics.com/design-hi-fi-audio-amplifier-lm3886
1) The input capacitor (C1) is to block any DC in the audio source. This explains it a little better:
"Cin is in series with the non-inverting input. It’s main function is to block any DC present in the audio source, while allowing AC (the audio signal) to pass. DC in the audio source needs to be blocked or it will be amplified along with the audio signal and create a high DC offset at the speakers. This distorts the audio."
3) C1 is only to block DC in the audio source, so the. capacitance doesn't have to be exact; just somewhere between 1µF and 4.7µF.
4) Who said C1 should be made of foil 🤨 . Electrolytical is usually used there.
5) R4 and C2 is the low frequency cutoff.
"The cutoff frequency of this filter should be 3 to 5 times lower than the Fc of the Cin\ Rin high pass filter at the input. If the Fc of this filter is higher than the input filter, the amplifier will pass low frequencies to the feedback loop that it can’t handle. This will create a voltage across Ciand cause DC voltage to appear at the inverting input, which will be amplified and cause distortion. Therefore, the input filter (Cin and Rin) should determine the lower bandwidth frequency of the amplifier, not the feedback loop filter (Ci and Ri)."
6) I'm not sure what R5 is. What I would put there, is a Thiele network, which consists of a resistor and an inductor.
"the Thiele network reduces oscillations caused by capacitive loads, usually due to long speaker cables. It also prevents radio frequencies picked up by the speaker wires from getting back into the amplifier’s inverting input through the feedback loop."
"The datasheet recommends a 10 Ω, 5 Watt resistor in parallel with a 0.7 µH inductor. In a stereo amplifier, there will be one Thiele network per channel. They should be located away from the amplifier’s input circuitry to prevent interference from the magnetic fields generated by the inductor."
9) I personally use EasyEDA, but I might be biased, as I have never used anything else. An added bonus is EasyEDA (PCB design), LCSC.com (electronic components) and JLCPCB.com (PCB manufacturer) are all together. So it is easy to quickly make a project and have parts and PCBs.
10) That has something to do with the ground loop. Usually to fix this, you would attach all the grounds from everything together at one point.
Hope this helps 😀
EDIT: Quotes from this very helpful website: https://www.circuitbasics.com/design-hi-fi-audio-amplifier-lm3886
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1) The DC voltage nor the impedance/resistance of the input is known. If C1 is omitted for DC response, any DC input will be amplified and appear on the speaker. The +in and -in are not strictly AC. They require connection to a zero VDC reference (+in) and the output DC voltage (-in) via equal resistances (R2, R3) so that the bias current from +in and -in exactly cancel.
2) C2 and R4 set the frequency where the feedback network transitions from (22+1)/1 to 1/1 at DC.
3) For a (22K+1k) input impedance, a 1uF capacitor transitions at 1/2piRC = 6.92Hz. 4.7uF => 1.47Hz 20Hz=> 0.346uF
Much below C2+R4 ==> 7.23Hz is perhaps pointless but not a problem if 4.7uF is more available. If you know the amp is for use with a small speaker, it is wise to deliberately cut low frequencies.
4) The bias current from +in is very small so there will be a very small DC offset on R2, and electrolytic capacitors do not like reverse voltage. This is not usually a problem, but purists will ask for an AC compatible capacitor, and some maintain that electrolytics create distortion similar to a diode.
5) In order to minimize output DC offset, the gain at zero Hertz (DC) should be 1/1. C4 is "open" at DC.
6) LM3886 uses a "quasi-complimentary" output because power PNP transistors on a chip cannot match NPN on the same chip. This means that the output circuit is a CFP aka Sziklai Pair which is potentially unstable and must be loaded at high frequencies to remain stable. And the main feedback loop may be destabilized by the phase shift of capacitive loads, so the output goes through an inductor (and/or resistor) to isolate the feedback loop from capacitive loading.
7) Additional feedback at high frequencies can improve distortion, and/or phase lead from a capacitor in the feedback can improve stability. But such capacitors should be limited with a resistor to prevent Radio signals from the speaker wires (antenna) reaching the input where they can become rectified into (interference) audio. Resistors are always the best way to attenuate radio signals because inductors etc simply store energy and have unpredictable high frequency behavior.
8) Distortion can be reduced by adding external feedback, but this tempts fate with stability problems and requires very careful feedback network design. As a beginner, you will have enough trouble getting a basic amplifier to operate stably.
10) If you use a switching supply, know that the AC input filter requires an earth ground connection, otherwise it will couple half the line voltage to your circuit ground. For analog power supplies, be aware of the currents in the main capacitors, rectifiers and transformer and avoid connecting to them twice, which will have a noise voltage between them.
2) C2 and R4 set the frequency where the feedback network transitions from (22+1)/1 to 1/1 at DC.
3) For a (22K+1k) input impedance, a 1uF capacitor transitions at 1/2piRC = 6.92Hz. 4.7uF => 1.47Hz 20Hz=> 0.346uF
Much below C2+R4 ==> 7.23Hz is perhaps pointless but not a problem if 4.7uF is more available. If you know the amp is for use with a small speaker, it is wise to deliberately cut low frequencies.
4) The bias current from +in is very small so there will be a very small DC offset on R2, and electrolytic capacitors do not like reverse voltage. This is not usually a problem, but purists will ask for an AC compatible capacitor, and some maintain that electrolytics create distortion similar to a diode.
5) In order to minimize output DC offset, the gain at zero Hertz (DC) should be 1/1. C4 is "open" at DC.
6) LM3886 uses a "quasi-complimentary" output because power PNP transistors on a chip cannot match NPN on the same chip. This means that the output circuit is a CFP aka Sziklai Pair which is potentially unstable and must be loaded at high frequencies to remain stable. And the main feedback loop may be destabilized by the phase shift of capacitive loads, so the output goes through an inductor (and/or resistor) to isolate the feedback loop from capacitive loading.
7) Additional feedback at high frequencies can improve distortion, and/or phase lead from a capacitor in the feedback can improve stability. But such capacitors should be limited with a resistor to prevent Radio signals from the speaker wires (antenna) reaching the input where they can become rectified into (interference) audio. Resistors are always the best way to attenuate radio signals because inductors etc simply store energy and have unpredictable high frequency behavior.
8) Distortion can be reduced by adding external feedback, but this tempts fate with stability problems and requires very careful feedback network design. As a beginner, you will have enough trouble getting a basic amplifier to operate stably.
10) If you use a switching supply, know that the AC input filter requires an earth ground connection, otherwise it will couple half the line voltage to your circuit ground. For analog power supplies, be aware of the currents in the main capacitors, rectifiers and transformer and avoid connecting to them twice, which will have a noise voltage between them.
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For 10)
I have a short view for better understanding, what my brother do for me, because of the 230V side.
Of course 50V are also not less, but better as 230V~ And the chance to get both together are small, so 25V is ok.
We make the red bridge and the China board do not make so much noise more without input.
May can help low pass coils as LC inner the Elko circuit ? so all under 50 Hz ? Is this the noise i heard ?
For 8)
I also draft a circuit what I found and what I please ask you what this exactly do.
I Think it is a kind of Feedback "e.g. like in DC/DC Step Downs" which give a information back to the beginning
and compensate anything. But what in Detail. I read so much , that this modification makes the LM3886 much better.
So first I want to understand what this should make in the circuit exactly. (also in red marked.
And last but not least
Thanks for help me 😍
I have a short view for better understanding, what my brother do for me, because of the 230V side.
Of course 50V are also not less, but better as 230V~ And the chance to get both together are small, so 25V is ok.
We make the red bridge and the China board do not make so much noise more without input.
May can help low pass coils as LC inner the Elko circuit ? so all under 50 Hz ? Is this the noise i heard ?
For 8)
I also draft a circuit what I found and what I please ask you what this exactly do.
I Think it is a kind of Feedback "e.g. like in DC/DC Step Downs" which give a information back to the beginning
and compensate anything. But what in Detail. I read so much , that this modification makes the LM3886 much better.
So first I want to understand what this should make in the circuit exactly. (also in red marked.
And last but not least
Thanks for help me 😍
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Hi Micha, can you please tell us your Mother tongue or Country of origin?
Google Translate is terrible and often mangles content, knowing which Language it´s translating from helps us "compensate" for some translation flaws.
Oh, and it will also help when suggesting pars suppliers, not everthing is available everywhere.
Parts easy and cheap to find in some Country may need importing or paying lots of Customs and Freight/Shipping in others.
And welcome to the Forum.
Google Translate is terrible and often mangles content, knowing which Language it´s translating from helps us "compensate" for some translation flaws.
Oh, and it will also help when suggesting pars suppliers, not everthing is available everywhere.
Parts easy and cheap to find in some Country may need importing or paying lots of Customs and Freight/Shipping in others.
And welcome to the Forum.
Of course you can 🙂
Yes, I use Google Translator, type in in german and copy paste to here.
I do not know what is more worst , my english or this from the translator. I think booth 🙂
Iám german woman so please name Michaela not Micha... Micha is a boy name 🙂
What do you mean with suggesting parts ? I do not suggesting parts ?
Or is this only a hint in advance, then thanks .
And thanks for the welcome greetings, fine to get so easy and good understandable answers.
Fine to be here.
Thanks and you are proving my point 🙂
.... in Germany and nowhere else, but how would we know? 🙂
Literally that.
When you want to modify/improve your amplifier (we are in DIY Audio 😉 we will suggest some parts, and obviously not "what everybody uses" because those will already be in your amp.
"Improved" parts are harder to find.
If you are in USA we will suggest, say, Mouser or Digikey, if in England Farnell or RS Components, etc. so again you see Country is important.
Even Canadian users, being side by side with USA, same language, etc. often have trouble when ordering from US suppliers because of Tariff and Customs barriers often paying WAY more in Tax-freight/postage than what the parts are worth.
You´ll like it here 🙂
PS: just a small detail: you chose the Micha user name yourself 😉 😉 , don´t blame me 🙁
I thought Micha was a friendly diminutive of Michaela.
Thanks.
Maybe you can suggest a list of popular German market DIY suppliers, for future reference.
Maybe you can suggest a list of popular German market DIY suppliers, for future reference.
Dear JMFahey,
First of all : SORRY SORRY SORRY i do not want to blame you !!!!
Yes you are right, Micha is alos a name für Woman. I must take Micha , because username Michaela was not free.
So you are right 🙂 !!! But one of my best freinds , a boy , has Micha for calling, für me its "Ela" ;-)
Of course I ( my fathers for me) buy at digikey here, by its private possible.
Not so cheap , but all most available.
So and now back to my questions and Topic.
-------------------------------------------------------------------------------------------------
It old you now a liitle more about my plans:
I want to do an 2.1 Amp with 2x LM3886 and 1x TDA 7293
I start now with the LM3886, because I get here in "EBAY Kleinanzeigen" from an older Men, which
is over 80 Years old, over 10x ORIGINAL new Ics.
Also he forwards me 5x TDA 7293 in ORIGINAL.
That why i come to this 2 kinds of CHIPamps
I make my first tryings with simple Transistor Amp, now I want to go into the 3886 Topic.
But so many in the technican Doku is not so clear for me and I have nobody which I can ask
in an "pupils" wise..... In school we do resistors networks, that all :-(
So back again,
My last post "Yesterday at 8:40 AM" for 8) and 10) , i was lucky if i can get here a little bit feedback.
A new Point 12)
I test yesterday a bit with high and low Pass circuits and see something.
I use first a NE5532 , because of DIP and Cheap, later i will use Analog or TI OPA series.
In High pass, the sinus of e.g. 1k is the same on input and output.
In Low pass the input sinus of e.g. 200Hz is not the same like the output.
I thing this is what are named phase shift, right ? Iam not sure if its 45° or 90°
I got from my grandma a simple Oszi from Owon, there I see it.
Is this normal, that the sinus is shiftet, and do not make this anything in hearing by ears ?
I see on my fathers subwoofer there is a 180° Switch controll and also a 0 - 180° Regulator.
But its not allowed for me to make tests and measurement with them 🙂 🙂 Maybe i make some defect 🙂
Is it the best if i make a circuit were I can also adjust all this thinks ? Whats are your opininos about that ?
Questins about Questions.... 🙂
What do you think, I think about this wise.
If i understand the most zu 70% 🙂 by myself and I make a circuit i would please show it here for discussion in advance
before i make all the work with EasyEda or KiCad.
So I´am ask please for best hints and tell my in your honest words , which is totally wrong or bad.
But also with explanation why, so I can understand.
Hope this could go here ?
(PS: this Text was without Google .... more worst or better ??!!!)
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Did you take a look at the link I mentioned? https://www.circuitbasics.com/design-hi-fi-audio-amplifier-lm3886/#Balancing-the-Input-Bias-Current
It explains in great detail every part of designing an audio amplifier based on the LM3886.
FYI, I personally haven't used the LM3886 specifically.
Sorry, I'm not able to answer 8) or 10) 🙁 .
I'm not sure what you mean here 🤔 .
It sounds like the switch is for on/off and the pot (0 - 180 deg) is for volume possibly. I personally add as many customizable things as possible to my projects, so I would say, yes, add a on/off switch and, maybe, 10kΩ potentiometer on the input audio to control volume.
👍. FYI, EasyEDA is quite simple to use. I always use it for all of my circuits.
I hope I did that 😉 .
Your English is quite good! I think your English is comparable to the translator.
Cool, thanks.
Yes, there "should" be some sticky thread suggesting best suppliers in every Country.
Yes, there "should" be some sticky thread suggesting best suppliers in every Country.
Dear kgray9,
thanks for your link.Thats a good text for start up.
Now I have at first some to read 🙂
I found some interresting info about composite mode.
But for this I thing i start a new Topic, also for the Subwoofer and the phase shift topic.
Also i was really interesset in elko, or foil in Polyester or Polypropylene was really an difference.
So Wima for example has so differnet types....
I can try all, but then it become to expensive for me, so i try to get many informations of experience in advance.
DIY Audio members, have a great sunday and thanks for the start up support to my 🙂
Perfect 👍 . That is what I do for every part of every project I make 😉 .
🤨 . What do you mean? Are you talking about capacitor types?
yes , exactly, I read that it make much a difference which type is use in audio signal paths.
Some say polypropylene are the best , but they are big in dimensions?
So what is better , small faktor like RM5 with low LC or big polypropylene with i thing , bigger, LC because of dimensions an d an RM of 27,5 insteadt og e.g. 5 ?
There I come to one of my biggest question i have actually in my head 🙂
How can I see if my result of PCB is good or not ?
Of course by ears and if nothing is swing ( oszillate ) in the Design.
Sure with the Oszi i can measure if the output is similar the same form as input ( insteadt of gain)
I make test with a PC signalgenerator on the China board...
I see on oszi if there is a phase shifting or clipping , but how I can see with simple methods
if my comming own PCB is better as a China board for 15€ ???? 🙂
Need I really a spectrum analyser for the e.g. THD measurements ?
Or can I do this by sound card and a good microphone.
My soundcard can handle up 192 khz because my father has so much Flag audio and i listen often now
WEB Flag radio.... so Input and output can 192khz and more.
No real idea, how to.... but If i make a own design i want to see real result, i thing my ears are not so fine.
🙂 🙂 how more I read, the more it becomes real interresting , i see AUdio is a big big big topic 🙂
Before i thing about Amp I heared MP3 and thats all, no thinking about all 🙂
Then I tried EasyEda today.... hmm simple using, but Via making i found on first eye complicate.
Must try a little more...
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Polypropylene is the best, but it isn't really necessary. Ceramic is also good for filters and such. I usually just use electrolytic.
LC? LC stands for Inductor Capacitor filter.
By listening, you can usually hear grounding problems and such, but other fine tuned things, need an oscilloscope. I still don't have one because they are so expensive, but I have searched before and came up with the answer of using an oscilloscope. If the amp doesn't have enough power, the peaks on the sound will appear cutoff, or flat.
If you really wanted it to sound amazing, yes, you would need a spectrum analyzer and all that to see the minute details.
Yes! Audio is a lot more complicated than people would think.