[sdiy] Experimental VCA RFC

[Jerry Gray-Eskue]

I have not specifically looked at that but the data sheet shows Turn-on /
off and Rise and Fall times well under 20 microseconds for the conditions
listed. 

My gut feel is that they will be plenty fast for most if not all audio
application. 

-----Original Message-----
From: Tom Wiltshire [mailto:tom at electricdruid.net] 
Sent: Friday, March 18, 2011 9:25 AM
To: Jerry Gray-Eskue
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Experimental VCA RFC

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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