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[moordenaar]

Hi..

I have a toy keyboard, and it's just a COB version. Normally I would throw it because it makes this irritating SQUEAKY noise when it's turned on.

But it has the most owesome bass and claps.

I've added an electrolytic capacitor across the power terminals, thinking it might be a dirty voltage supply but no.
I've also replaced the LM386 chip, but still the same prob.

Any hints ? I need this squeaky noise gone. I thought about maybe adding a LP filter, but then the claps would suffer !

[noystoise]

what kind of keyboard is it? what do you mean by squeak?

[moordenaar]

It's a black blob circuit + LM386 amp.. Has some drums + patterns + some diff. piano sounds.. Very simple stuff.

The squeaky noise is just a annoying whining but it's a problem if you want to use it for more than fooling around..

I'll record it but I don't know where to upload it..

[Remork]

if you want to rule out the dirty PSU, run it on batteries.
batteries don't have ripple so they don't induce noise.
if you're already running it on batteries and it squeaks, it's the circuit.

sorry if that's stating the obvious to you 

[Gordonjcp]

If it squeaks when you run it on batteries, it could be that the batteries aren't up to the job.

Why not just make a circuit that mutes the output for half a second when you turn it on?

[moordenaar]

No worries remork.

Gordon: It's a continious whining noise. Both on batteries (duracell might I add) and on PSU..

Haven't gotten around to recording it yet as I'm having a "small" problem with my MBox2..

[noystoise]

what kind of keyboard is it? do you have a picture? what mods have you done? can you describe them?

[moordenaar]

It's just a simple toy keyboard.. black blob circuit + LM386 amp..

I have not made any modifications yet..

[Remork]

try audioprobing it? aka half a cable through a (guitar) amp, with its sleeve connected to the circuit's ground, then touching points to listen (through a smallish cap) with the center lead..
just to see if the whine comes from before or after the LM386.
input pin is either 2 or 3, depending on how they used it.
power supply is on pin #6 (you know how Ic pins are counted counterclockwise, right?)

more info on the audioprobe:
http://www.newtone-online.nl/forum/index.php/topic,2432.0.html
in het nederlands weliswaar, maar dat lijkt me geen probleem voor een moordenaar.

[moordenaar]

Haha nice rijmend. Ek praat afrikaans al is. Dus laat ons hou aan engels. 

I will try your suggestion..

[Remork]

deal 
unintentional rhyme there, thanks for pointing that out