[sdiy] DC offset removal help

cs e modulemania at gmail.com
Wed Aug 13 18:40:35 CEST 2008


Thanks for all of the ideas, guys.

Harry, with the Germanium and the Pull Down, how does that look?  You
said it would be "choppy"?

On 8/13/08, harrybissell at wowway.com <harrybissell at wowway.com> wrote:
> If you substitute Q2 (2N3904) with an NMOS transistor (such as a VN1206)
> and use the shottky diode, you can do even better
>
> With the shottly alone, simulation says about 78mV residual...
> the NMOS transistor takes that down to 24mV
>
> H^) harry
>
>
>
>
> On Wed, 13 Aug 2008 08:38:17 -0500, harrybissell wrote
>> 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 synth-diy.org
>> > http://synth-diy.org/mailman/listinfo/synth-diy
>>
>> Harry Bissell & Nora Abdullah 4eva
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org
>> http://synth-diy.org/mailman/listinfo/synth-diy
>
>
> Harry Bissell & Nora Abdullah 4eva
>
>


More information about the Synth-diy mailing list