Buzzy audio

[dmlloyd]

I just finished laying in my s-video circuit for my 600XL. It worked great, so next I moved to adding an audio out. This was straightforward - I just connected to the old modulator audio input. But after I started it up, I noticed that a couple keys on my keyboard stopped working - probably from unplugging the ribbon so much - so I took the ribbon out and buffed it, reconnected, and the keyboard started working again - and then I started getting this awful buzzing on the audio output.

 

Sound is still audible - SIO serial bus and sound out sounds and GTIA clicks all work - but there's the ever-present buzzing noise. Since it was an easy thing to test, I swapped out the op amp chip but there was no change. The next thing I'm thinking of trying is replacing the coupling capacitors one by one, but I'm hoping that someone here might have another idea I can try first, that maybe involves less mayhem to my poor system's guts.

 

Thanks in advance for any advice...

[MEtalGuy66]

Check your grounds.. And use a shielded wire for the audio..

Edited May 30, 2010 by MEtalGuy66

[dmlloyd]

Fixed it by taking the audio signal from a different point in the circuit. Not sure why it's so much better though - some impedance issue or something maybe...