MATRIXSYNTH: Doc Sketchy DIY Videos

Friday, March 09, 2018

Doc Sketchy DIY Videos

Published on Mar 9, 2018 docsketchy

This one in via John L Rice.

Doctor Sketchy is David G. Dixon, who designed a few Intellijel modules. Check out the David Dixon label for some of his previous creations.


1. Doc Sketchy ASR Demo
Here's a little video of my ASR module. This is my improved version of the CGS (Cat Girl Synth) ASR from Ken Stone. I have added some extra useful features, such as Shift/Bypass switches and a Load/Loop switch, which is pretty fun to use. I've also added an input attenuator, which to me is crucial. I put a new PCB that I had just stuffed for a customer into my existing panel to test. I found that it was really drifty (like, portamento drifty) -- the culprit: a dodgy LF444 opamp used for the S&H buffers. I bought some LF444s at a local shop (originally sourced from Digikey) and they are all crap (either defective or counterfeit) -- I had forgotten. Anyway, I replaced it with a TL064, and there is no drift at all. I'm also using 100n film caps, so those are large enough to avoid obvious drift if the input bias current of the opamps is reasonably low.

2. Doc Sketchy Dual Interpolating Scanner Demo
Here is the dual scanner, all put together and ready to send to its lucky buyer. I'm feeding it with the outputs of 4 VCOs, with two up-octave outputs into inputs 5 and 6, all tuned to a chord. Here I'm mostly playing with the switch that selects either two independent 4-channel scanners or one 8-channel scanner. It all works perfectly -- I just wish those little pots were a bit further apart. As usual, boards, bare or stuffed, and complete modules are available. Just ask (preferably on Muffwiggler).

3. Doc Sketchy Interpolating Scanner Demo
Here is the second demo of my new interpolating scanner circuit, with the improvements suggested by the Muff Wiggler beta testing team. I'd still like to figure out how to get the CV to maintain a constant range as the Width pot is adjusted, but I haven't so far. In any case, the Fader and Width pots are doing exactly what I want them to do.

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