[sdiy] should I BUILD SOME SYNTHS ???

[harrybissell]

lol!

while you guys are debating the prose and cons of analog vs digital
recording
(I'm with the D boys btw... I use dat)

I have been building synth modules.  Most specifically an old EFM VCF 2e

(Moog ladder style).   I did not populate the funky envelope follower or
the
envelope generator... just the filter section.

My main complaint with the Moog ladder is the loss of volume when you
crank up
the resonance. This is a 'feature' of the design.

This particular filter has an OTA to give VC resonance.  (LM13600) ...
with the
OTA output going to the opposite NPN tranny from the input.

I added the buffer to the circuit... so the OTA output goes to the
transistor base...
AND the buffer.  I take the buffer output and sum it with the normal LPF
output.
Now when the resonance is zero, there is no output from the OTA and the
LPF
is the only signal from the summer.  As the resonance is increased...
the LPF
passband is dropping BUT the signal from the OTA resonant feedback path
is INCREASING...

giving a pretty good compensation for the loss of volume.

This trick would probably NOT work with the standard Moog style
resonance pot (essentially
a resistor)... but if you make the pot an attenuator and fed the
resoance from the wiper
(adding a suitable buffer) it would probably work.

Hey what do you think ?

H^) harry