[sdiy] DC offset removal help

[harrybissell at wowway.com]

Pulldown resistor value isn't critical. I'd use 47K
because I like to have some current but not too much current :^)

I think that 10K is too low a value for a lot of circuits, and maybe
100K is too high. 49.9K is my favorite compromise.

You might find that the cutoff is a little 'choppy'.  Probably a re-design
would help. If you can send me a copy of the schematic I might figure
a better mod. One way might be to make some kind of negative supply...

(remembering from uhhhh... memory :^)

H^) harry



On Tue, 12 Aug 2008 10:22:45 -0600, cs e wrote
> It's the old EFM Dual ADSR...running off of a 556.  I don't know if
> there are schematics online.  But like I said, there is essentially a
> .2 V offset right after gate, and it eventually settles to .1 V.  I'm
> going to try a OA90 (the only germanium I can find here) with a pull
> down like Harry suggests - what value of pull down resistor, 10K?
> 
> On 8/12/08, cheater cheater <cheater00 at gmail.com> wrote:
> > What envelope, what schematic...?
> >
> > On Tue, Aug 12, 2008 at 3:36 AM, cs e <modulemania at gmail.com> wrote:
> >> I've got an ADSR envelope here, which has a TL072 as output buffer.
> >> Unfortunately, there's around a 200mV DC offset on its output, with no
> >> gate applied. (This won't allow my VCA to shut off properly - I know
> >> the VCA is OK, because I have other envelopes.)  Of note is that the
> >> 200mV reduces (over a long time) to around 100 mV or so.
> >> How can I easily and quickly remove this offset...I don't mind if 200
> >> mV is chopped off of the output.
> >>
> >> Thanks for any ideas.
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Harry Bissell & Nora Abdullah 4eva