Several LM386 on same board

[mihozu]

Hi

I try to make a single board with 8 inputs, 8 LM386 to be able to drive 8 speakers with different sources.

As the simplest circuit (input on 3, 2 and 4 grounded, output thru 250uF) was satisfying on breadboard I've put 8 of those on a single board.
Then it appears that the output on speaker is pretty noisy.

I have no idea how i could get the minimal noise level I got from a single LM386 circuit.

Does anybody have any clue?

Thnaks

[expanoncolin]

It could be the power supply you're using, or the power supply could be acting poorly because you're drawing too much from it, or there is some noisy cross-talk between the power lines, or the board you put it on is not well-isolated so there is some feedback.  Try putting filtering capacitors on the power supply line (basically a 100 uF or so with + to V+, - to GND, and a .1 uF to V+ and GND in parallel).  Try connecting the LM386's to the supply one at a time, and see if it gets noisier as you add more.  Check your soldering to make sure there are no bridges or anything of the sort that might allow for amplifier instability.

-Colin

[mihozu]

Colin
Thanks for quick answer.
Actually putting a 100p capacitor in parallel with power supply solved most of my problems.
Now I'm pretty satisfied with the noise level.