[sdiy] Looking for blend circuit?

[cheater00 .]

PNP and NPN resistor. Biasing them changes the gain. No VCA.

On Fri, May 17, 2013 at 6:49 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
>> Everyone,
>>
>> I'm looking for a blend circuit that at center position there
>> is no output, turn it left from center and you get just input
>> A then turn it right from center you get just input B. Using
>> VCAs I can do this but that would make what I'm doing to big.
>> I need to keep it simple/minimal using op-amps, pots and diodes.
>>
>> Any suggestions?
>
> Set up a potentiometer between the +15V and -15V rails, and send the wiper
> voltage to a buffer, and an inverter.  Use the outputs of the buffer and
> inverter to control two
> linearized 2164 VCA circuits (see here:
> http://www.edn.com/design/analog/4336650/Op-amp-linearizes-attenuator-contro
> l-response).  Feed A into one VCA and B into the other.  This circuit will
> do what you want.
>
> In this circuit, the VCAs only operate with a positive CV.  A negative CV
> renders them inactive.  Hence, only one VCA will be active no matter what
> the pot setting.  At fully CCW, A will be amplified at unity gain, at fully
> CW, B will be amplified at unity gain, and in the centre, both will be off.
>
> Parts count: 1 pot, 1 V2164 chip (Small Bear Electronics), six opamps,
> various resistors and caps.
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy