[sdiy] Analog envelope generator offset

Tom Wiltshire tom at electricdruid.net
Fri Oct 31 12:47:57 CET 2014


Hi All,

I'm playing with an analog envelope generator at the moment. This is something new for me since all the envelopes I've done thus far have been digital.

I noticed that there seems to be a 400mV offset on the output voltage. However, when I started testing it, it seems like it is just the very last bit of the release curve. The output rapidly falls from the sustain level to about 300-400mV, but then takes another full 20 seconds to reach something measurably close to zero.

I realise that in theory it should *never* reach zero, but do all analog envelopes behave like this? When you trigger a quick series of envelopes, it amounts to a considerable offset (it would be several semitones) in the interval between the envelopes. Are there tricks used to eliminate this effect? I've checked several available ADSR schematics and none of them seem to do anything different - a cap feeding a TL08x voltage follower seems to be standard, and the cap just gets discharged to ground. If what I'm seeing is typical, these designs should all have this "offset."

I'm just looking for some pointers really, since I don't know what to expect.

Thanks,
Tom


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