[sdiy] reducing crosstalk

[Derek Holzer]

Hi all,

A bit of a n00b question... I'd like to know about general strategies 
for reducing crosstalk between channels in an audio circuit. For my 
TONEWHEELS project, I have 8 phototransistors modulating 6v DC as 
shadows pass over them. I was running this directly into my audio mixer 
for a while, as well as using it for control voltage. But then I came to 
a point where I needed the circuit buffered to send it to some audio 
processing modules in my synth.

When the whole thing was just a raw connection, I didn't get any 
crosstalk between the channels. Now, each channel comes to a board, and 
goes through two inverting op amps (two channels of a TL074) before 
going back out again. The voltage going to the phototransistors is 
resistance-divided from the +12V supply for the ICs, without a 
regulator. There is currently no decoupling at the inputs or outputs, 
only some 0.1 uF caps on the + and - rails. The circuit is 
hand-constructed on perf-board.

There is crosstalk between all the channels, not just the channels which 
share an IC.

Where should I start with this? Is the crosstalk coming from a bad 
grounding? The ICs? The connection wires? I'd be happy to upload a photo 
of the circuit and a drawing of the schemo if that would help. In 
general, where would such crosstalk come from? Do I need to etch a board 
with a good ground plain? Since I want to use the output as either audio 
or CV, high-pass caps for DC removal isn't an option. Or is it?

best,
d.

-- 
derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
---Oblique Strategy # 111:
"Lowest common denominator check
-single beat
-single note
-single riff"