[sdiy] Booster for Synthacon VCF

[Michael Ruberto]

Hi

I was tinkering with the Synthacon VCF and added a simple FET amp to boost 
it's output. To my suprise I got something quite more than I anticipated. It 
does work properly - a 1Vpp signal in gives me a 2Vpp signal out with the 
resonance cranked and a 1Vpp at min res. However, I also get the sweetest, 
warmest, tube type sound I've heard lately. It's really quite delicious!

On the O-Scope I see a rounding off of the linear portions of the waveform. 
With a sawtooth on the filter's input and cutoff completely open, the 
waveform is a quarter circle shape. It seems I am overdriving the FET.

Drawbacks, The VCF will not oscillate due to the loading down of it's output 
tranny. Might be worth it to add an op-amp buffer between the stages. This 
is basically a simple preamp and it can be used by itself or with any other 
module too.

Give it a try, you won't believe your ears!

M. A. Ruberto