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Synthi inspired project - Microdec back end

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Synthi inspired project - Microdec back end

by schmidtc » Wed Nov 30, 2011 19:01 UTC
Hi Peeps,

I'm working on a synthi style project that will have a Microdec as the final stage in the signal path. The design is still being worked out (suggestions?), and will include a combination of commercially available PCBs and some breadboarding. . .

PCBs:
- Microdec
- 3 VCO's with vibrato of Jurgen Haible's design http://www.jhaible.de/living_vcos/jh_living_vcos.html
- MOTM filter, not sure which one yet.

The DIY bit will inevitably get a bit messy, but it should be managable:
- 556 based dual ADSR
- OTA based VCA x4 (joystick (2), Filter (1), amp (1))
- Ring Mod
- Pre-amp / envelope follower / gate extractor
- Pink / white noise

If there's room I'd also like to add sample and hold and an LFO. I may add an OTA based voltage control to the MOD1 pot on the microdec, and perhaps a circuit that cycles through each oscillator at the gate signal. Synthi style patchbays are expensive and you need to hack the diode/shorting pins to resisters in order to sum the signals, so the matrix is scaled down a bit to 14 x 15 2.5mm jacks. There's still plenty of room on the panel, and matrix size is the biggest constraint on all the cool features I want to put in. Here's a picture of the panel as of this morning, Microdec at bottom left.

image

More to come!

Re: Synthi inspired project - Microdec back end

by schmidtc » Wed Nov 30, 2011 19:26 UTC
Matrix routing. Everything else like gates, the master keyboard CV and the audio path will be normal'ed

Sources (14 total):

1. Pre-Amp
2. Oscillator 1 (2 rotary switches determine the waveform, 1 for normalled audio path, 1 for CV)
3. Oscillator 2 (same)
4. Oscillator 3 (same)
5. Joystick X (-5V to 5V max range)
6. Joystick Y (-5V to 5V max range)
7. Joystick / VCA mix out
8. Ring Mod
9. Noise
10. ADSR1
11. ADSR2
12. Envelope follower out
13. LFO
14. Sample and hold

Destinations: (15 total)

1. Oscillator 1 FM
2. Oscillator 2 FM
3. Oscillator 3 FM
4. Oscillator 1 PWM
5. Oscillator 2 PWM
6. Oscillator 3 PWM
7. VCA 1 input
8. VCA 2 input
9. Ring Mod in A
10. Ring Mod in B
11. Filter CV
12. Resonance CV
13. Depth CV (shared by Chorus and Vibrato)
14. Rate CV (shared by Chorus and LFO)
15. Microdec ADC 1

Re: Synthi inspired project - Microdec back end

by guest » Wed Nov 30, 2011 22:34 UTC
wow
that panel came together fast

if you want to control the mod pot
you could just send it a votlage directly
by cutting the trace that runs from the wiper to the uc
and put a shorting jack in there
so when you plug in a jack
it cuts out the pot and has the external drive instead
youd have to put a level shifter in though