My home made sans amp changes its sound after 15 seconds

[trapiche]

Hello!

I have this problem: My home made sans amp worked during months withot problems....but suddenly it started to sound very bad (sometimes like a whistle or like very uggly distorion...it seems to be coused by OPAMP in charge)
I thought that opamps were broken so I changed them....
but after 15 seconds the same thing happend....
If I turn it off and wait a few seconds, it sounds ok again....BUT only for 15 or 20 seconds....
please....help me find the problem...

thanks

[niftydog]

schematic?

I'm willing to bet a cap in backwards maybe?

[trapiche]

hello!

I used tonepad layout and my opamp are tl072...
It worked during months without problems!!!

:?

[niftydog]

yes, I read that, but maybe the cap finally gave up the ghost and is not working properly.

It's apparently a heat/current related problem that takes a short while to appear after it's first turned on. This is not likely to be caused by a resistor, and you've already checked the op amps... so by process of elimination I would, if I were you, be checking electrolytic capacitors.