[sdiy] Help, I'm Desperate! (Charge Injection with DG408)

Roman modular at go2.pl
Tue Dec 11 22:19:43 CET 2018


I know it's too late, as the circuit at this stage has already gone slightly different path, and I already gave up, but couldn't help drawing this little schemo that explains my idea of using single switches with that obsoleted chip. Switches should be DG444 or similar (0=closed, 1=open), or replace diodes with NAND gates and use any regular dirt cheap switch like 4066.  There's no switching happening while VCA is open, provided that VCA control triangles match the edges of LM3914 stages. The only switched channels are the ones routed to muted VCA, so in theory there should be no clicking audible.  Basicaly this is just the circuit that makes this input switching sequence:  VCA-A:12233445566..  VCA-B:11223344556...  by creating one step overlap between stages. Only 6 inputs in this example, but can be extended to any other number.  www.synthdiy.eu www.synthdiy.eu   IMHO switching active channel will always produce some clicking for many reasons: not matched channels, difference between transistion times H->L and L->H as Ingo said, break-before-make feature of DG407, slow response of 4532, and who knows if not also charge injection.   Roman  Dnia 11 grudnia 2018 18:24 Ingo Debus <igg.debus at gmail.com> napisał(a):  Am 11.12.2018 um 08:10 schrieb David G Dixon <dixon at mail.ubc.ca>:   There is now  only one tiny problem: There is still an almost imperceptible click when the  CV crosses 0V (and the logic control voltage crosses 2.5V) in the positive  direction.  This is when the logic switches from 011 to 100 (i.e., all three  bits change).  Interestingly, I don't hear the click at all when the CV goes  in the other direction (100 to 011).   Couldn’t this still be caused by a very brief „forbidden state“ during the transition from 011 to 100? In your case, the forbidden state would be 000 (MSBit changes slower that the other two) or 111 (MSBit changes faster). Probably just a difference between rising and falling slope. Can you check with a scope?   Ingo  ______________________________  Synth-diy mailing list   Synth-diy at synth-diy.org  synth-diy.org synth-diy.org
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