vchadsr troubleshooting

[jimsmiley]

Hey all. Just trying to wrap my head around the vchadsr at the moment. (http://www.jhaible.com/jh_vc_hadsr.pdf) I have two semi-working homebrew boards, both identical, behaving the same. Attack and Release both work beautifully, however, I can't get the decay stage to do anything, and sustain just raises or lowers the overall voltages of everything.
I cheated somewhat, using 741's as u7B, and u6a, and lf412 as u8/u9

D2 looks as though it is meant to pull high after a certain threshold, turning q6 on, , however, it seems like q6 is always on no matter what, , pulling r6,r7 low, never allowing q5 to short r9. There's the briefest of pulses on the base of q5 when triggered.

Any ideas as to what I should be seeing in this area?
Cheers, Jim

[jimsmiley]

Fixed - changed the 1N cap to 100N, and all working great so far, in my quick tests. Time to finalise a layout and build a few for a polysynth project - appears to be a really great design for such a thing with the level of fine tuning available.
The hold function's been disabled by omitting all parts, except for 18k to negative. Have to add some sort of gain control for my filter contour also

[Highcooley]

Hey Jim

This topic is a bit old, but I try it anyway 😀 I just built Ninni Bergfors' version of Jürgen Haible's ADSR generator (http://hem.bredband.net/bersyn/EG/VCADSHR_s.pdf) and it behaves exactly as you described your problem. However, as it seems Ninni's circuit already uses a 100n capacitor. You don't by chance have any idea how I can track down this problem. I still haven't figured out a 100% how the circuit actually works, so it's difficult to get my head around the problem. It is also not clear to me which inputs do need additional input resistors (the sustain definitely does and the attack as well). In addition, do you have a copy of JH's circuit. Since his passing, the schematics and descriptions are nowhere to be found.

Thanks for your reply!

Cheers
Andy

[jimsmiley]

Pm'd you a schematic. Can't recall if I did anything else other than change that cap - I did up a pcb layout, but was obviously too lazy lazy to write in component values. I made a bunch of boards, that all worked great - but ended up going with something smaller...
I'll take a look out in the shed and check one of the boards to see if anything's vastly different from the schematic

[malmi315]

"D2 looks as though it is meant to pull high after a certain threshold, turning q6 on, , however, it seems like q6 is always on no matter what"

I do the Bergfotron one.

I have the same problem with it. Any Ideas ?