[sdiy] Experimental VCA RFC

[Tom Wiltshire]

Very interesting Jerry.

How fast can it respond? I see you've got about 40ms attack time there. I'd expect there to be a significant lower limit with optos, but perhaps it depends entirely on the type.

Thanks,
Tom

On 18 Mar 2011, at 13:08, Jerry Gray-Eskue wrote:

> Request for Comments:
> 
> This is a link to a VCA design I have been working on using H11A1 Optos as
> voltage controlled resistors.
> This includes a PSpice schematic for the core, and two PSpice plots at 20
> and 60 degrees C.
> The biggest design challenge is keeping the circuit from being effected by
> temperature changes, U3D uses the Thermistor NTC3 for this purpose.
> U1C is just the signal in buffer, U4A,U5 and U6 are the control /
> attenuation circuit. R15 sets the current per voltage in for the LEDs of the
> Optos. U4B is a just a spare at the moment.
> The Schematic shows H11A2s which seem to share the same PSpice model with
> the H11A1.
> 
> In the plots the Green line is the envelope voltage, the red line is signal
> out.
> The signal in not shown is 1000hz at +-5v
> 
> 
> http://myweb.cableone.net/ankh/VCA.htm
> 
> Jerry Gray-Eskue
> 
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