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Old 3rd February 2011, 05:49 PM   #1
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Cool LM386 amp Capacitor suggestions

Hey Guys
I built myself the HeadBanger headphone amp few months ago...its working fine, but i'd like to improve the sound quality of this amp....can i use JRC386 ics inplace of the default LM386s? also, what caps should i change and what type should they be for more bass? wider soundstage and more detail?

also i have read about input caps affecting DC Offsets. This amplifier has output caps (i guess they are called so) and no input caps...with the load connected, my multimeter measures 0VDC.is it that the author has substituted input caps rather putting them at the output stage?also, putting input caps degrades signal to some extent, so does putting the caps at the output remove the negative effects of input caps (Bass Roll-Off, Cap distortion, Phase distortion)?

Project Homepage: HeadBanger Headphone Amp Construction Kit
Schematic: http://www.minidisc.org/schem.gif

Thanks in Advance
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Old 9th February 2011, 10:11 PM   #2
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For more bass increase C3-C7 to maybe 2200uF.
For sound quality many things need to be considered, for example decoupling power supply caps, layout and grounding.
You can increase also C1-C5 to 100uF.
C10-C9 should be near IC; cable from 9V battery to C10-C9 should be short and twisted.
I think you can use JRC386 but it is unlikely it would improve sound quality!
Output caps degrade signal as and more than input caps but an amp can still sound good provided they are big enough.
Didn't understand question about multimeter showing 0 Volts.
Fell free to ask more.

Last edited by Davide82; 9th February 2011 at 10:20 PM.
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Old 9th February 2011, 11:06 PM   #3
Minion is offline Minion  Canada
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Well the LM386 is a pretty noisy chip so it is probably the limiting factor not the capacitors and there aren"t any low noise replacements for it cuz it isn"t a standard opamp ........

also you need to have the output cap , because the chip is a single supply chip it will have half the supply voltage on the output so the cap it there to block it , Increaseing the value of the output cap will give you better bass responce .......

I would suggest you keep your headphone amp the way it is and maybe build a new one useing Low noise opamps , Maybe a Cmoy ??
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Old 10th February 2011, 08:16 AM   #4
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Weel, yes you're right; the LM386 is noisier than typical headphone amp; but I used it with tamed down gain (as in the schematic we're speaking about) and with inefficient headphone (not earbuds!) and it was dead quiet and really good listenable. Even the author of the original schematic seems pretty good impressed.
I have to say it did much difference switching between an iPod direct connected and an iPod+LM386 in my case; my friends were astonished. Of course, if you use it for really efficient speakers it is not well suited.
The strong point here is that this amp is simple and can sound good.
Trying some mods doesn't take much time!
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Old 10th February 2011, 11:02 AM   #5
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thanks for the replies minion and davide82

my question with the multimeter thing was that, are output caps better compared to input caps?

also, minion, i built the CMoy too, the power rating of this amp is better, also building it i came across hell lots of oscillation issues (wish i had posted this before, as the info provided by davide82 could have helped avoiding these issues)

so output caps should be 2200mF.thanks davide82.
also what about decoupling power supply caps?this one's built around one 9V battery, and 220mF electrolytic cap, + 0.1mF ceramic is what i have placed on my board...should i change that too?
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Old 10th February 2011, 11:14 AM   #6
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To your questions:
1) Generally speaking, usually it is more convenient to find better input caps because they don't need to be so big and so you can use other better types such as polyester or polypropylene instead of aluminium electrolytic); bear in mind that in this amplifier topology it is mandatory to have an output caps because you don't use a simmetrical supply and the amplifier is single ended instead of BTL (bridge tied load)
2) Personally I would use 220 uF on pin 6 (without ceramic); 100 uF on pin 7; 2200 uF as C7; avoid C2 (as in http://gilmore2.chem.northwestern.ed...itar_prj.htm);
3) pay attention to layout: everything should be placed really close to the pins of the LM386.
4) should you have problem with offset, you could try an input cap before pin 3; I suggest to try a 470 nF polyester (small box); try it if it makes any difference... maybe you have some offset and you didn't know...
5) it's probably that R2 is implicated in the oscillation because you lowered the gain; try to increase it to 22k if you STILL have problems (but I happened to make it work with something as low as 15k).

Last edited by Davide82; 10th February 2011 at 11:20 AM.
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Old 9th April 2012, 12:24 PM   #7
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Default Caps on LM386

To learn how to put the proper capacitors on a LM386 chip, check out:

How to Connect a LM386 Audio Amplifier Chip to a Circuit

It shows complete wiring necessary.
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