[sdiy] CV inputs with bipolar "amount" knobs

[Grant Richter]

Hi Harry,

John Blacets "Mixer/Processor" module MX2040 uses center detent pots  
with trim pots such that you can get a null of -60dBv or better at  
the detent.

This is the best version of this type of module ever made. Period.

Any arguments, meet me behind the bar!

On Jul 19, 2010, at 8:46 AM, Harry Bissell wrote:

> One way involves using an opamp with standard resistors in the  
> inverting section, and a pot
> with one end at the CV input, the wiper to the non-inverting input,  
> and the other end at ground.
>
> with the wiper at 50%, the circuit has the same levels at inverting  
> and non-inverting inputs and
> nulls to the common mode rejection of the opamp (maybe not that  
> good...)
>
> The second is to make buffer of an opamp and an inverting buffer of  
> the same signal. Wire a pot as
> a load between the two opamp outputs, and take the (bipolar CV)  
> output from the wiper. This could get
> a much better 'null'.
>
> Use a center tapped pot, and ground the center tap and this circuit  
> would work very well !
>
> (I oould send you a schem if you like, contact offlist)
>
> H^) harry
>
>
>
> ----- Original Message -----
> From: Tom Wiltshire <tom at electricdruid.net>
> To: Synth DIY <synth-diy at dropmix.xs4all.nl>
> Sent: Mon, 19 Jul 2010 09:24:01 -0400 (EDT)
> Subject: [sdiy] CV inputs with bipolar "amount" knobs
>
> Hi All,
>
> I know various people have built various devices with CV inputs  
> that have bipolar "amount" knobs so that you can easily invert a CV  
> input - particularly useful for envelopes and such like.
>
> How many different ways of doing this are there? Can anyone provide  
> a reference to a schematic online?
>
> I just had a big hunt around thinking I'd find loads, but mostly  
> they must be parts of other circuits 'cos I couldn't find any.
>
> Any pointers appreciated.
>
> Thanks,
> Tom
>
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> -- 
> Harry Bissell & Nora Abdullah 4eva
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