The VCDM – Voltage Controlled Digital Modular Chip

The VCDO and the VCDF have been deprecated.
They are now joined into a single chip, the VCDM.

Voltage controlled Pulse wave oscillator with separate PW and detuned SUB output.
0-5v CV input for pitch. Range C2-C7. 1volt/octave.
0-5v CV input for pulsewidth 50-95%.
Main osc output 0-5v swing.
SUB osc, -1 octave 0-5v swing.

White Noise Generator
0-5v output.

Voltage controlled digital 18dB lowpass filter with resonance.
0-5v unipolar audio input (can be lifted to +-2.5v bipolar)
0-5v CV input for Cutoff frequency.
0-5v CV input for Resonance.
Filter PDM output with 0-5v swing (requires passive LPF)

Voltage controlled digital amplifier.
0-5v CV input for filter level.

A singel voice analog hybrid synth in one chip.
Same price. $35

Order the VCDM Chip

The manual can be found at the site


If you have ordered either the VCDO or the VCDF you will automatically recive the new chip including both functions.



35 Responses to “The VCDM – Voltage Controlled Digital Modular Chip”

  1. Gary Says:

    Hi Jan
    I’m having problems with my VCDM chip. I’m getting a signal from the square out and the sub out, but they are both very glitchy and sound like morse code. The noise out appears to be fine. Any suggestions?

  2. Gary Says:

    No, well stabilised 5 volt supply

  3. Gary Says:

    I’m supplying the cv in with 0-5v through a 10 k pot used as a voltage divider. Could that be the problem?

  4. janostman Says:

    Is it the same if you connect the CV directly to ground or Vcc?

    You could try a smaller pot.

  5. Gary Says:

    There doesn’t seem to be a problem when the pot is at either extreme, so that could be the problem. I don’t have a smaller pot to try it with. What value would you suggest? And how could I feed the cv input from lfo’s. Would I have to change the output pots on those as well?

  6. janostman Says:

    It doesnt like high impendance signals ( above 1-2Kohm) and long wires if you have it on a breadboard.

    Thats no problem with an LFO as the output impendance is less than 1K.

  7. Gary Says:

    I’ve not managed to resolve the problem, and it’s also glitchy with a LFO input. Do you think a buffer on the CV input would help?

  8. janostman Says:

    Put a 100n/0.1uF cap across the Power supply near the chip.

    Also try a 0.1uF cap from the viper/CV input to ground.

    • Gary Says:

      I’ve tried both of these with no success. I’ve reflowed all the solder joints as I thought it might be a loose connection. Buffering was my last hope!

  9. janostman Says:


  10. janostman Says:

    From where does the LFO voltage come?

  11. janostman Says:

    Your not putting more than 5v or less than 0v on the CV input?

    • Gary Says:

      0v and 5 v are coming straight off the supply rails. LFO is a simple square and triangle generator built from two op amps. The glitchy output is not fluctuating in frequency, it is cutting in and out, which makes me wonder whether the problem might be with the output of the oscillator rather than the input, although the problem is with the sub osc as well, but not the noise output.

  12. janostman Says:

    I’m trying to figure what could be wrong?

    • Gary Says:

      Thanks, much appreciated

    • Gary Says:

      Hi Jan
      I thought the problem might be caused by the stripboard layout so I’ve breadboarded the chip. Noise and sub osc outputs are fine, but I’m still getting problems with the osc out as follows. CV input direct to earth – low frequency tone, no problem. CV input connected to a voltage divider of two 470 ohm resistors – stuttering mid frequency tone which cuts in and out once or twice per second. CV connected to 5volt supply – stuttering high frequency tone. There is no frequency modulation, the tone just cuts in and out irregularly like a morse code signal. I’ve tried two different power supplies with the same result. I am beginning to think that the chip might be damaged. Would it be possible to return it to you for testing?

  13. Gary Says:

    Hi Jan
    I tried the chip on a breadboard with short wires and a 1k pot for the VC freq in, but it’s still stuttering, although not nearly so bad as before. I’ll return it to you tomorrow for a replacement unless you can think of anything else I could try.
    Thanks again

  14. Gary Says:

    Hi Jan. Just to let you know that the replacement chip hasn’t solved the problem. The chip is very glitchy and I’ve given up with it for the moment. I might go back and have another try to get a useable output from it at a later date.

  15. John Says:

    Hi Jan – I’m also having the same problem as Gary. I’ve put the VCDM chip on a breadboard, my PSU is clean, I have decoupling capacitors on the power rails, but I’m seeing the osc and sub osc out wave drop a few cycles periodically, (a couple of times a second) on my scope. Noise out is fine, filter and VCA working normally – it’s just the osc dropping out. Gary’s description of it sounding like morse code is accurate. Any suggestions on how to resolve?

    • janostman Says:

      Hi John, I’m investigating the problem. If there is a firmware problem you will receive a new chip.

      • John Says:

        Thanks Jan – looking forward to the resolution, because otherwise this is an amazing chip. Please let me know If there’s any tests, or extra info I can provide to help diagnose the problem.

      • John Says:

        Hi Jan, Since I purchased one of the earlier chips with the problem reported in this thread, could I get a replacement with a chip that uses the higher sampling speed?

  16. Gary Says:

    Hi John
    When Jan replaced my chip, the new one exhibited the same problem. I never did get to the bottom of it, so let me know if you figure it out.

  17. Gary Says:

    Hi Jan
    I’ve just breadboarded my chip again and it’s still showing the same dropout behaviour that John described. Have either of you diagnosed the problem yet?

    • janostman Says:

      I’ve changed the sampling speed on the ADC on later chips and have not recieved any complaints yet.

      Do you want another one?

      • Gary Says:

        That would be good. I’d really like to build this great little synth. I think you already have my mailing address. If not, let me know. Do you want me to return this chip? If so, what’s your address

        Thanks, Gary

  18. John Says:

    Hi Jan – I posted earlier about the chip having the dropout problem from the osc. It looks like in your reply to Gary you might have sorted that problem out? If so, can I get a working replacement?

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