MPS Impact Generator

Silesius · Joined: Feb 12, 2010 Posts: 65 Location: Berlin

Hi, I've been building some drum modules based on the "Electronics Drum Cookbook" and other Thomas Henry designs, but I wanted to add the MPS active impact generator, which seemed very nice.

So I've built a couple of them with the idea of adding them to a pair of Bass++. The thing is I built one first, tested it (in 3 minutes I must confess), and it seemed to work fine. Then I built the other one.

Now, while testing them more deeply I notice I can hear the sound of the 4046 VCO even when the VCA is closed. Of course is not a very loud sound, but its quite noticeable, specially at high frequencies. I checked everything and it seems there's no mistakes. Besides, this happens to both circuits, so I guess I made no mistakes. I'm using +-12v and a stripboard.

So I imagine the problem is in the VCA... but the VCa is very simple and I can't find what I did wrong (if I did something wrong). I tried adjusting the voltage divider made with r86 and r5 and this lowers the volume of the bleedthrough, but of course it also lowers the whole VCO so this is not a solution. I just want the VCA to be quiet!! Anybody knows how to do that? I also wonder if your MPS's show the same problem. Can you hear the 4046 vco without trigger? I can hear clearly the pitch sweep of the VCO when I turn the pitch pot (Ok, no very loud, but it's there and I don't like it Crying or Very sad

Any ideas?

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