3340 oscillator demo

Just wanted to say thanks for the help on the threads I started on integrating with VCV Rack. I put a demo together at the link below: this is a board I developed that has an oscillator, a CEM 3340 clone. A bunch of switching logic & CV signals are are controlled from a VCV Rack module developed specifically for this board. This is basically “proof of concept complete” phase of the project.

Plugin code, custom board, and other stuff is on github. I’m hoping to take it a ways further; I’m wrapping up a board revision in the coming weeks.


damn was hoping this oscillator was modelled in rack. but that is dope.

No way I’d even think of modeling it, nothing like the real thing!

I’ve gotta say: having owned other 3340 based synths (Prophet 600, MC202)… being able to modulate it any which way from Sunday via other modules in VCV Rack is pretty eye opening. That’s eye opening as in, “wow, a single oscillator can do THAT!?” I’ll be getting some docs out on build info and such after the next board revision. Pickup a soldering iron and get onboard! :grinning:

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Can’t wait … Will you be selling kits ? or do we start sourcing the BOM’s ourselves ?

Planning on making a module using the CEM3394 / AS3394? (six or more)?

I’ve not thought that far ahead but it’d likely be towards the latter: here’s the BOM, Gerbers, and documentation. The board itself just uses SPI and I2C, so it’s not specific to any particular platform. One could target an STM32, Arduino, or something else. I’m using a Pi Zero since that makes it easy to take advantage of Alsa for audio & MIDI as the incoming controls.

Thanks for the link to that CEM3394 project. I hadn’t seen it, that’s a pretty incredible project. It looks in principle similar to what I was going for: have some host board where this & a half dozen modules could plug into.

Interesting project. I have an Electrosmith 3340 which I love. Have the same scope (the 100MHz version) too :slight_smile:

A bit tangential but that tiny USB bus board - did you make it or buy it?

Guessing you spotted the power supply- it’s from Synthrotek. USB power and two Eurorack power connectors. I got the bare board & built it up myself; the Recom DC-to-DC converter for +/-12 is a bit tough to find & Synthrotek didn’t have any in stock. Think I got the Recom chip from Mouser. Not the cleanest power supply but pretty useful power supply for a limited space setup.


The Electrosmith board is pretty cool. This board I’ve put together is quite a bit different, since the interface is digital (SPI, I2C) it would be interfaced with a microcontroller. That and the Electrosmith board is a ton cheaper than what I’ve got. The DAC alone is about the same price as the Electrosmith board. Getting costs down is tough.

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Thanks for the link & info. What a nifty little thing.

The 3340 really is a great sounding oscillator so I will be very interested to see your final build. I guess the cost is what it is - if you’re mainly doing this for yourself rather than for commercial release it’s not something to worry about too much.

Perhaps for a lower price, use a low-cost single channel 12-bit DAC, followed by a multiplexer, with sampling capacitors on the outputs, for a multiplexed 8 channel output.


Inspiration from Moog slim phatty. (DAC8581 followed by 4 x DG408 for 32 DAC outputs )

Yup, sample & holds would get DAC costs down a bit. I’m not sure if it would be that efficient for this use case though. Typically, you’ve got a microcontroller’s bus directly attached to the sample & hold multiplexors. To do similar with the interface I’ve defined, one would have to use a GPIO expander to do the round robin of the S&H multiplexors. I dunno, it could work, it just seems like a lot of overhead with I2C/SPI transactions that may slow things down. Versus one SPI transaction to just set the value and move on with a multichannel DAC.

Another factor of DAC selection was trying to find something in a hand-solderable package. The 12-bit 8-channel from TI I’ve got was the only thing I could find in a SOIC package. There’s cheaper options and you could even bump it up to 16 bit resolution if you want to solder a TSSOP package. hmmm, just noticed that JLCPCB have an 8-channel 12-bit DAC for a decent price; it’s a TSSOP package but JLCPCB could do the assembly. Thinking…

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Hey there! As you (all) seem to embrace the 3340 - has anyone first-hand experience with wavefonix 3340 VCO? - I‘d really like to hear somethiing about it… Thanks in advance! Cheers, dDom