[sdiy] VCA response - continously variable between linear andexponential

cheater cheater cheater00 at gmail.com
Sat Mar 2 08:28:08 CET 2013


David, that may look like a good idea, but it's different - it's
mixing lin and exp. It's not going to give you the same range of
sounds you could get from a circuit which can vary the exponential
base.

Cheers,
D.

On Sat, Mar 2, 2013 at 5:21 AM, David G Dixon <dixon at mail.ubc.ca> wrote:
>> i'm looking for some advice/pointers on how to get a VCA
>> response curve to be continuously variable between linear and
>> exponential. i can do switchable between the two, but is
>> there any trick to getting everything inbetween?
>>
>> if it helps, my VCA is lm13700 based but i don't mind
>> starting with something else.
>
> I don't know how to do it with an OTA, but it's pretty easy with a 2164 VCA,
> if you start with Mike Irwin's circuit from EDN -- the last article in this
> PDF: http://www.edn.com/file/18017-72502di.pdf
>
> The thing to do is to add a separate CV inverter which feeds the amplifying
> VCA's VC pin directly for the exponential response.  The CV output from this
> and the CV output from the linearizing servo can be connected to the poles
> of an SPDT switch, with the centre terminal going to the VC pin of the
> amplifying VCA, or the switch can be replaced with a pot, with the wiper
> going to the amplifying VCA's VC pin.
>
> I'll send you the schematic (sorry, I have no website).
>
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