[sdiy] Schmitz ADSR replace pots with CV control?

Mattias Rickardsson mr at analogue.org
Tue Nov 26 09:41:34 CET 2013


On 26 November 2013 08:19, David G Dixon <dixon at mail.ubc.ca> wrote:
> If you put a resistor in series with a 2164 VCA, then you essentially have a
> voltage-controlled resistor. When the VC pin voltage is 0V, then the
> resistance is that of the fixed resistor.

The normal way of connecting the 2164 is at an OP-amp's virtual earth
summing node. Then it's true that it "looks like" a variable resistor
seen from the OP-amp's point of view, since the 2164 provides a
current that is VC controlled.

But from the 2164's input side, it doesn't. It's just a regular fixed
resistor connected to another virtual earth. So it will not, say,
drain a capacitor in a voltage-controlled manner with its input. Also,
the 2164 is supposed to be connected to a virtual earth in order to
behave as specified, so I'm not sure if you could just put a 2164 in
the place of the pots in the drawing, regardless of the voltages
around them. But I haven't tried it! :-)

>  This worked extremely well in the Quadra.

Hurrah!

/mr


> ________________________________
> From: navelludd at gmail.com [mailto:navelludd at gmail.com] On Behalf Of Mattias
> Rickardsson
> Sent: Monday, November 25, 2013 10:48 PM
> To: David G Dixon
> Cc: synth-diy at dropmix.xs4all.nl; Jack Jackson
> Subject: RE: [sdiy] Schmitz ADSR replace pots with CV control?
>
> I don't quite see how that would be done with a 2164... do you have a
> sketch? :-)
>
> /mr
>
> Den 25 nov 2013 22:17 skrev "David G Dixon" <dixon at mail.ubc.ca>:
>>
>> No, a single 2164 would do nicely, with one VCA to spare.  The response
>> would be exponential, as it should be for an envelope.
>>
>> > -----Original Message-----
>> > From: synth-diy-bounces at dropmix.xs4all.nl
>> > [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of
>> > Mattias Rickardsson
>> > Sent: Monday, November 25, 2013 7:38 AM
>> > To: Jack Jackson
>> > Cc: synth-diy at dropmix.xs4all.nl
>> > Subject: Re: [sdiy] Schmitz ADSR replace pots with CV control?
>> >
>> > With Vactrols, would be the simplest solution... if you can
>> > live with the drawbacks of slow CV response and possibly
>> > weird range. Anything more advanced would require a very
>> > different circuit, I'm afraid.
>> >
>> > /mr
>> >
>> >
>> > On 24 November 2013 19:52, Jack Jackson
>> > <jackdamery at hotmail.co.uk> wrote:
>> > > I was looking at René Schmitz's  ADSR 2. It looks like a
>> > neat little
>> > > design, but I was wondering if it would be possible to
>> > adjust it to take 0-5v CV for the parameter control instead
>> > of using potentiometers directly in the circuit?
>> > >
>> > > http://www.schmitzbits.de/adsr2.png
>> > > _______________________________________________
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>



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