Home-made Modular Synth teething trouble

[Phil Callaghan (Core Design Ltd.)]

I have built a simple modular analogue synth from designs in R.A.
Penfold's book "Electronic Synthesizer Construction" with a few modules
of my own.

I get problems when interconnecting the modules, and I can't figure out
what is wrong due to my limited knowledge of electronics.

Most of the modules seem in interact in ways which are not acceptable.
For example, I connect a noise generator to a op-amp amplifier and the
noise cuts off above a certain volume. I thought that maybe it was
necessary to put a buffer between the noise and amp, but this made no
difference. Then I tried to smooth the power supply rails using
capacitors, but this didn't work either. Another such problem is the VCO
starts to oscillate when I connect an LFO to the S&H.

I have been reading books on electronics, but none of them shed any
light on this interconnection problem. I think this must be a basic
modular problem and wondered if anyone here could point me in the right
direction.

Phil Callaghan