Using what parts I have left I’m building another little rack mount mono synth. Twin VCDCOs based on the HAGIWO $9 VCO and an AS3372e filter and Electric Druid chips for LFO, EGs and Noise source. Haven’t published anything about it yet as I’m still working out the kinks, but I have both VCDCOs under MIDI control.
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LFO and noise circuits working as expected after a scare with a faulty LFO chip not putting out the correct waveforms.
I’ve now modded the DCOs to accept an FM/pb input on the mod CV input, so I can seperate out the v/Oct CV from the FM for better control.
I will mix the MOD control pot with the LFO like was suggested in another post if I want to implement modulation of the wavefold.
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There are people in this group with far more experience than me, I’m just gluing stuff together and seeing what sticks. But thanks for the compliment.
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Sort of finished, portamento doesn’t work yet, noise is not connected and I’ve not added the waveform modulation as I said I would, but generally I’m happy. I think a little calibration of the frequency range is in order, I’m feeding both synths from the same CV and dividing resistors but I think that internal voltage regulators can vary the tracking. I hope you like it so far.
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Fixed up some of the issues and features today in-between air raid sirens.
Noise is now connected to the filter, white noise was incredibly low compared to pink, found an open circuit on the CV feed to the white noise VCA level.
Both Seeeds now powered from one 3.3v supply has fixed the tuning variations I noticed earlier.
Added a final VCA for the volume instead of a 10k linear pot, now the output volume is CV controllable.
Added LFO to wavefold modulation, thanks to the ideas from clarionut I managed to mix the wavefold pot and LFO together to allow modulation of the wavefold.
I want to try some of the mods suggested by clarionut, including the PWM of the square wave and Neopixel led indication of the waveform.
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I’ve started addding schematics and code to my github page if anyone wants to take a peek
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Finally done, I managed to chop the tops off some clear 5mm LEDs to act as diffusers for the Neo pixel LEDs to give it a more natural look like a real LED.
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This came out top tier. Can’t wait to hear it!
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Final build, all things fixed or implemented that I can find to do. Some strange stuff going on in that Elkyam MIDI to CV code, he took 21 away from the note message meaning it was 3 notes out on bottom C. I added +3 as a temporary fix until I studied the code more carefully. Fixed version is on my GitHub site.
Fixed all the issues I can find, Portamento is working, MIDI to CV has been recoded to fix bottom note issues, master tune, noise etc all working now. Added Neo Pixel LEDs to display the waveform by colour otherwise you get a bit lost trying to match or find the waveform. Added LEDs to the EG outputs to show envelope etc. Pretty much everything is voltage controlled so I could add a mux/DEMUX and make it programmable but the wave selection technique doesn’t lend itself to that I would have to change it to a pot and there are no more ADC inputs left on the Seeed. Oh well food for thought.
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Holy crap. Sounds great as well as looking amazing!
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I know it’s finished, but I already have plans to modify it.
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Fix the Elkyam MIDI to CV converter so you can change MIDI channel from toggle switches or a bank of 4 dip switches.
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Add a little programmer based on an Arduino and a shift register just to add other functions that can be stored in eeprom.
a) LFO sync to MIDI
b) LFO sync to external input
c) Envelopes log/lin option
d) LFO multiplier options
Anything else that springs to mind
In fact I’ve just realized I could probably change the MIDI channel as well from the programmer.
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Man, this thing is fantastic. You did a great job. It sounds great, looks great and fits right any mount. Well done. I’m going to looking to the specs to see what I can learn/get inspired to do.
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I created a GitHub page, it has 26 repositories of my projects, I have started documenting this one on there. Some are complete, others need more documents. To be honest, besides noting the pins used to connect to the motherboard I built this without making any documents or notes, it was pretty much build it and see and modify as needed, so anything I have documented is from memory or borrowed from other projects.
Midi to CV was the Elkyam design with mods and additional channel change option.
VCOs were HAGIWO $9 with mods by myself and clarionut
Filter was by polykit and again tailored for my build
EGs and LFO were designs from Electric Druid again tailored for my use case
Noise was Electric Druid with my design of a fader between pink/white.
Most of it is on the GitHub page with the mods
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I’m going to revisit this project and in the original design I built a lot of the options with voltage control which lends itself perfectly to microporcessor control. The stumbling block is the waveform selection, it just uses a single push button input to increment to the next waveform and then cycles to the beginning of the 8 waves. So, I was thinking, if I replace the Seeed XIAO RP2040 with a RP2040 Zero which has more GPIO available but still in a compact size by adding 4 pins or so along the bottom edge of the device. I need 3 pins to select 0-7 on the RP2040 to select the wave. I’ve got a couple on order to test and when I’ve finished with the PolyKit 16 I might see if I can add a Teensy based mux/demux to read and write the parameters and store them in memory.
Just FYI - the RP2040 Zero not only has the extra 5 GPIOs on the bottom edge of the board, but also another 9 (plus GND) on tiny pads on the underside of the board. Tricky to connect to perhaps, but there if you really need them. See File:RP2040-Zero-details-7.jpg - Waveshare Wiki
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Yeah, I was just looking at the difference between the two yesterday, I actually only need 3 pins for the wave selection.
My plan is to make an adaptor board so I can slot the Zeros straight in with as little work as possible on the rewiring and to have the header coming out to the wave selection.
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