[sdiy] x0xb0x background noise problem

[Louis van Dompselaar]

I've already posted this to the x0xb0x forum but I think there's
a lot more experience out on this list ;-)

I have just finished building #149 for someone else (after doing my own) 
and it worked first time round 
(http://www.dompselaar.org/x0xb0x/149/x0x149_02.mp3) but on closer 
inspection there is a constant background noise in there. It also 
amplifies VR8 (volume) slider movement. I tried a replacement for VR8 
(different type and brand) but that sounds exactly the same, so it
doesn't seem to be related to that pot.  The noise is present on VCA 
output anyway. I can actually see it on the scope.  If I get the time
I'll try and trace it back down.  I *think* the VCO and VCF were clean
when I first tested these in isolation.
Power lines are clean, at least in the ranges my scope can manage.

I would've just put this down to it being old circuitry, but since my 
own b0x doesn't have this (it's actually extremely noise-free), it must
be something else.

Here's the background noise (much amplified) with me moving VR8:
http://www.dompselaar.org/x0xb0x/149/x0xnoise.mp3

Any obvious things that come to mind that would cause this?


Louis