[sdiy] CV inputs with bipolar "amount" knobs

[cheater cheater]

You got me curious. Shat does he do that it's so good?

On Tue, Jul 27, 2010 at 00:59, Grant Richter <grichter at asapnet.net> wrote:
> 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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>
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