• analog monster

    Hi, I stumbled upon your blog through electro-music, I’m really interested in this project and was just wondering if there is any progress – I see there are a few samples on soundcloud. I was hoping to find a schematic but the link from electro-music doesnt work and I cant find it anywhere else.

    I am building a synthesizer for my dissertation. The idea is to try to use only currently available components and to have an entirely analog signal path. I’ve already designed and built waveshapers for tri, pwm and sine, looping env generators using 555s and a discrete vca based on the korg MS-20. I’m still undecided on filter, I was going for a 13700 ota design but the looping envelopes reminded me of the polivoks so I am now seriously considering the filter from that. The sticking point is I’m struggling to get a dco saw core.

    It would be really helpful if I could see your circuit, as any analysis I have attempted to make of similar DCOs (juno 106, cem 3396) has the component values missing as they are internal to the chip.

    On a side note, thank you for your hard work on the arduino midi library, I have used it for many projects – step sequencers, midi controllers, midi to trigger devices for pre midi drum machines, and I am sure many future projects too. Looking forward to seeing it develop further. Cheers

    • Francois


      I made some progress, yes (I actually rewrote the whole code, it began to become a bit messy), but I haven’t had the time to post anything yet. The analog saw core part is not yet working, on the old design I had something “almost” working but the schematic was too complex for such a simple task, and the result not very good (bad amplitude tracking over the whole range). So I’ll start over on this part as well, using 16bit PWM for the exponential signal feeding an integrator, clocked by the MCU. From there on, it should be a matter of tweaking a few resistor values to get a flat response.

      The Polivoks is a great choice, a bit hard to drive and to keep tamed, but it surely sounds great! I’m experimenting on it with a friend, there have been some nice studies by Dave Brown recently, available here:

      That sounds like a nice project!

  • analog monster

    Sounds like we’ve been struggling with the same issue then. Even when I limited the range the amplitude still was too variable to derive the other wave shapes to a degree I was happy with. Oh well, I’m sure I will figure something out in the end. Yeah I have seen that polivoks page, very interesting. I stumbled upon the guy he based his work on in my early stages of module building and a polivoks clone was on my ‘to build’ list straight away, so it is great to see someone has developed the circuit further. Good luck, I’ll be keeping an eye on your blog, you have some really interesting projects going on