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LM386 amp buzz?

Should be an easy question :-)
I built my first 386 based amp, and it works great, except for input volume control. Almost every schematic has 10K pot at input (connected to pin 3 on 386). Problem is when I turn pot all the way down I hear buzzing noise, especially if source is off. Also it doesn't cut source volume noticeably so I tried using 10M Pot, and it works except buzz is now super loud. So how would I control volume? 

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Re-design4 years ago
If it doesn't gut the source volume when turned down the either it's defective or you have it hooked up wrong. The source comes thru that pot so turning the pot HAS to vary the source. Unless your source is running 100 or so amps.

Check your wiring again and make sure you have it hooked up right.
Its important to post a link to your schematic.  Some of them are just drawn wrong.

What do you have the ground connected to coming off the source pot?
bratan (author)  Re-design4 years ago
This is schematic that I used:
http://web.mit.edu/6.s28/www/schematics/lm386.htm
I tried with and without C2 (on default gain of 20).
If there's a better one please let me know and I'll try it.
I don't think it's PSU, since I tried from different power sources including battery.
The buzz/hum that I'm talking about is usually heard on most amps when you turn gain very high and it's just amplifying noise. I'm just surprised that it's coming when I put a resistor between pin 3 and ground (bigger resistance, louder hum/buz).
I will recheck my breadboard... I thought it was a know issue with 386 chip, but looks like not...
Oh one more thing, I don't know if it's important but my chip is not LM386, at least it doesn't have "LM" Marking, it's old chip that came with Radioshack Electronics lab.
Bigger resistance = more susceptible to noise, not less !!

It could be your grounding scheme, it could be lack of filtering on your board, there's a slew of things to check for - like a big, fat cap across the supply ON THE PINS of the 386, or connected close by by heavy traces. 1000uF at a minimum, 2200 uF if possible.
Your PSU is injecting noise into the system and/or its picking up radiated noise from something else. You need to post some pcitures of the rig you have, and some of your circuit diagram
bratan (author)  steveastrouk4 years ago
I got it working, thank you so much guys! I basically redid all wiring again from scratch and now it actually works great! :) I suspect that issue was that I forgot to connect 100nF cap between Pin 6 and ground, and also Pot was connected incorrectly, but I'm not 100% sure. Strangest thing is, I swear sound quality was much better before (in the incorrect schematic), now I'm getting too much bass...
Look for some tone control circuits to use on the front end.
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