[sdiy] DC offset removal help

[harrybissell at wowway.com]

Looks to me like if you replace D5 and D8 with 1N5819 Shottky
diodes, the problem will be pretty much gone. The lower drop should
remove most of the offset and get you much closer to the rail.

Its not perfect.  Perfect would probably use an analog switch so that
there is essentially NO voltage drop (just a tiny teeny time error).

H^) harry


On Tue, 12 Aug 2008 20:54:57 +0100, Tim Stinchcombe 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.
> 
> If the schematic I have for that is the one you have, then I think 
> that the residual 100mV is the collector-emitter saturation voltage 
> of Q2, which is hard on with no gate applied (the main cap 
> discharges through the release pot, a diode and then Q2). Thus if 
> you could find a nifty way of lowering Q2 emitter, wthout upsetting 
> the gating action, then that would probably solve it - I actually 
> have a simulation of that circuit from years ago for another problem,
>  but at the moment I'm fresh out of 'simple' ideas that might work
> (brain addled from a long day...)
> 
> Tim
> __________________________________________________________
> Tim Stinchcombe
> 
> Cheltenham, Glos, UK
> email: tim102 at tstinchcombe.freeserve.co.uk
> www.timstinchcombe.co.uk
> 
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy


Harry Bissell & Nora Abdullah 4eva