hi… Concerning my home built modular system another query crops up.
With the T1 control set at 2 (Attack) and slight amount of T2 (Decay)added i.e. between 2-5, a very considerable percussive “thump” is heard when key is depressed. Backing off the Attack T1, alleviates the “thump” and the T2 Decay also has an effect on the “thump”. Is this a normal type of thing for all modular systems, has anyone noticed this effect? I’m wondering if it is the 911’s or 902’s that may need recalibrating.
The circuits I use are from the Norlin 1978 schematics.
I found that having built the 911 I got no responce whatsoever until by trial and error (much error) a strategically placed resister near the flip-flop
got it to work.
Sounds like your VCAs.
Try putting an audio signal into a CV input of the VCA.
Do you hear or see the waveform on the scope?
If so, you don’t have good CV rejection from the VCA(s.)
It shouldn’t matter what the env gen is doing- you shouldn’t hear any thumps.
Best tools here are your ear and/or a scope.
Good luck 
Thanks Kevin..I have to borrow a scope to do that but will have a look.
Meantime, tackling the problem today I have found that the 911’s seem to kick out too much signal into the VCA. By attenuating the 911 CV out via the CP mix to the VCA the problem seems to reduce a good deal (but so does the general volume. )
In the wiring schematics am I correct in hard wiring (via the 8 switch Trigger and Envelope Voltage Panel) the 911 CV output to one of the three 100K resistors on the relevant VCA input? I cant see any sort of attenuation on the schematics or anything in between.