[sdiy] Analog envelope generator offset

[Girts Ozolins]

Hi, Tom,
if you have quick trigers, of course you'll not reach 0, because envelope
will retriiges before that. But check Erica Synths EG, that uses bit
different approach than conventional ADSR generators. Schematics are
downloadable there.
http://www.ericasynths.lv/en/shop/3550-polivoks_ish_adsr_eg_diy_kit.html

Be well!

Girts

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Tom Wiltshire
Sent: Friday, October 31, 2014 1:48 PM
To: synthdiy diy
Subject: [sdiy] Analog envelope generator offset

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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