[sdiy] Silonex optocouplers

[Grant Richter]

Hi Tim!

The subject of audio optocouplers is pretty subjective.

I reviewed the Audiohm products. In general, they are slower than their
Vactrol counter parts.

BUT, if you build a Buchla Lowpass gate out of a Hamamatsu ultra high speed
optocoupler, it will sound like a Korg MS-20 not a Buchla Lowpass Gate. An
even slow optocoupler will have a different sound to it.

So the optocouplers themselves and their attack and decay times figure into
the finished sound.

This is actually good, as you can get two different results from the same
circuit using different optocouplers.

As always, the best results are obtained by experimenting until you find
something pleasing to your ear.

Actual response curves vary by at least 30% so expect to use a lot of
trimmers for zero and span.

> From: Tim Parkhurst <tparkhurst at siliconbandwidth.com>
> Date: Wed, 23 Oct 2002 15:21:44 -0700
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Silonex optocouplers
> 
> Hello All,
> 
> Has anyone tried the optocouplers available from Silonex? They have a very
> wide range of parts along with some ap notes and schematics for audio
> applications. Maybe a good Vactrol substitute? Maybe even a replacement for
> the now defunct Burr-Brown VCA610 in powered speakers (Peter G)?
> 
> http://www.silonex.com/audiohm/index.html
> 
> The web site states
> "Silonex Audiohm optocouplers are ideally suited for high performance audio
> circuits. Most "design-ins" have demonstrated proven performance benefits
> over silicon based audio control devices such as VCAs and FETs. Audiohm
> optocouplers act in a circuit as a passive component, like a resistor, but
> are very dynamic. Effectively the component is a current controlled variable
> resistor."
> 
> They list Allied as a distributor. A check showed several of the items in
> stock, and prices ranging from about 2 to 4 bucks a pop. The NSL-32SR3 looks
> particularly interesting. It ranges from 60 Ohms to 25 Meg (!) and has a
> 'decay time' spec (time to 100K after removal of current through the LED) of
> 10msec. Might make for a fairly wide range VCADSR.
> 
> Tim Servo
> 
> 
> 
> 
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