electronic percussion – part.1 (hit hat)

After being sick as hell for few days, I managed to violate some neurons and get them back to work.

When I need to create some “drum” pattern on the modular system, it necessitates few essential modules (vca, noise, attack generator, and such…) which is a pitty considering that my system is (for now) rather small. I’ve built a TR808 thingy (which needs additional gain to match the modular standard) but it is quite large. I want something smaller.

Basically  I need a drum bass (boom boom boom), a kind of snare (tac tac tac) and a striking white noise (tchiiiiinnnn) to simulate hi-hat or Crash. This post is all about the latter :


perc_noise_jpgA white noise source into a variable high pass and going into a VCA which is controlled by a crude enveloppe generator. OTAs are always a bit of pain, they want very small signal to avoid distortion and create offset. But on the other hand they’re quite handy and reduce the component count nicely. Some AC coupling caps remove the offsets anyway.

I’m not really happy with IC3B and IC1B which buffer and offset the modulating signal to act on the OTA gain. That’s a bit ugly and R27 might interfere with the the discharge of C3.

however, it works very well as it, R40 is a trimmer (but will be replaced with a voltage divider) that brings an offset to the modulating signal and moves it toward the negative rail (to close the VCA properly).

I found the high pass filter more interesting that the traditional low pass for such application.

Some values are still to be determined hence their absence on the schematic.

One drawback remains, you can clearly hear a “poc” sound with the enveloppe being triggered. I though it was an issue on my design but all my VCAs do it with fast enveloppe (but they’re all made of OTAs…).

The snare and Drum could be indentical structurally, juste replace the white noise source with a sinus oscillator. Althought it could be more fun to do something else.

and I’m still looking for (cheap) reliable front panels (maybe acrylic but my experiences with it weren’t great).



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3 responses to “electronic percussion – part.1 (hit hat)

  1. Andrew

    As far as control panels go, I was thinking of trying thin printable film. I thought I would make my own legends in Paintshop or Twisted Brush and print them off and use a clear film to protect the print. The films listed below are quite thin, 80 to 100 microns



    I don’t need the control panel legends yet but I will probably start experimenting in a week or two. If you are interested, I’ll let you know how I get on.

    PS. I had given-up on electronics, but reading your posts got me back into it…..This synth is costing me a small fortune, and it is all your fault !! lol Ha,ha

    • sorry if my posts are making you in hard situation moneywise, hahaha…But that all stuff is so interesting and relaxing to me.

      For control panels, I don’t mind the absence of labeling (a DYMO sticker is quite sufficient for me) but the real problem is to have a robust panel. Engraved MDF could be enough but 3mm is too big
      to mount properly the jacks. I know that some people are using acrylic but It’s a bit fragile I think. I think there’s a german manufacter who uses PCB material for front panel but this can be quite pricey as well I guess. There’s also a guy in the UK that makes (made?) front panel on demands, but at the time it was about 5U moog-style module (that was on Yusynth forum)

      Some guys used printed films as you listed for guitar pedal use and worked good (pedal are more badly used than synth module).

      For small HP, I bought 3 doepfer blank panels and they will do the job nicely I think. But trying to find larger HP blank (cheap) is quite a hard task. Unless I can find a metal sheet shop or something to cut the metal at the right dimensions.

      That’s really tricky, it’s the only obstacle I have right now to finish some of my circuits.

      thank you very much for your interest !

  2. Gordon


    1. Using a psuedo random noise generator, it’s basically digital white noise. Then passing this through an hpf then a comparator to make it into a digital signal. This can then be filtered or sent straight to the vca.

    2. A variation on the Roland 40106 based metallic noise generator. It is possible to tune the 6 oscillators by adjusting the supply voltage. By feeding back some of the output ( of the six oscillators mixed together ) back to an opamp mixer that in turn feeds the 40106 with a modulated supply voltage. If this is unclear I can draw up a block diagram to clarify the idea. Anyway the result is quite similar to the psuedo random digital noise generator source, though a bit more metallic in character.

    3. Frequency modulation using harmonically unrelated frequencies , like 1 KHz & 1.4KHz, works best with square wave vco’s.


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