Quad Octoginta II

Since the CEM3340 chip was put back into production, and after seeing what a few other makers have built with them, I decided it was time for me to come up with my own take on this ‘tried and true’ chip! I looked over the various designs on using the CEM3340’s and settled on the Octoginta II.

Now that the VCO’s were sorted and I was able to purchase the DIY PCB’s, I needed to choose a wavefolder design. I like what Yusynth did with Haible’s wavefolder and went with his design here:


The YuSynth design required me to make my own PCB’s. This can be a laborious process if you have not done it before. But I have the process down to a science here in the lab, so I was able to get these made pretty quickly. Taste the Sodium Persulfate in the air, aahhhhh!

First I downloaded the PCB mask template from the website and scaled it to size. Then I burn a screen and print the mask onto the bare copper clad board. Then etch the copper off in a tank of Sodium Persulfate, rinse and let dry. Then drilled the holes and fixed whatever needs to be fixed.

Next step was to design the layout of this massive 72HP beast. It took a couple of redesigns before I could get it down to ONLY 72HP wide 😀 Here I output four CEM3340 chips into four YuSynth Wavefolders and out to a four pole joystick. Lots of sonic real estate! This will also be my second go at creating a synth voice, my first was taking 3 WMD Spectrums and creating the TRISPECTRUM. You can find that first creation here:

The inspiration for this build and using these particular chips is to try and satisfy my want for a Oberheim OB-Xa! Hopefully Behringer will be able to produce an affordable clone soon, but in the meantime…

Once you complete initial testing, it’s on to assembly. You need to figure out a timeline for installation when combining so many elements. You will save yourself loads of frustration if you think through the process of what needs to get installed first, next etc….

I knew right from the beginning that this design would NOT be skiff friendly. Meaning that it would be a ‘deep’ module. When planning my custom cases I like to have one 3U row be a deep one. This gives me a place to hold these large custom creations. Next post I will go over where this large module will call home 😀

6 thoughts on “Quad Octoginta II

  1. An interesting module! It would be nice to see the Quad Octoginta II and the -previous, TRISPECTRUM come out either as a DIY Kit or Complete product. I never seem to find any MMM products for sale though. Maybe some day?

    • Thank you, the problem with releasing these beasts into the retail realm is cost. You would have to be at and around $1K, so that will push a lot of people out. I was hoping to inspire others to look at some of the more affordable CEM3340 DIY kits and see what they might come up with on their own. Happy modding 😀

      • It would be great if you and Behringer teamed up on a collaboration for this design to possibly get it under 1k, but I think they have so many products on the horizon already.
        I see MMM products and I drool.

      • Have you thought about pushing the design / pcb patterns out onto Google or GitHub?

        Frankly the $1K does not scare me away. I just bought a Synth Tech E370 and that was right around the 1K mark. Guess the functionality comes at a price. Seriously believe though that this would easily sell as a DIY kit with PCB, Faceplate, and BOM. Think iSapien agrees.

        • I left links to where I found my info and inspiration. What you do with it is up to you. I did not document this. I made one for myself. I hope your journey into eurorack rewards you like it has done for me.

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