[sdiy] Re: LDR decay time

[Paul Higgins]

Hi Harry,

I don't really know if the optocouplers in the Mutron III are selected 
or not.  Probably it wasn't necessary because they were using 
commercially available optos.  But if you're building a Mutron clone 
and rolling your own optos, you might have some laborious matching to 
do.  You'll probably also have to build a current-source jig to do the 
testing.

I haven't looked at the Mutron schematic in a long time; the only thing 
I remember is that it's a fairly generic state-variable filter with the 
tuning resistors replaced by optos.  The sidechain is kind of neat in 
that you can do sweeps that are inverted (i.e. the harder you play, the 
lower the VCF sweeps).  The response of the optos is the real magic in 
that box.

-PRH

On Wednesday, April 28, 2004, at 09:34 PM, harrybissell wrote:

> Hmmm... do you really suppose that Musitronics hand picked the
> optos in the Mutron III ???
>
> Of course, hand matching cells might be done / a good idea in a stereo
> compressor where it would be noticed.... and I have heard phaser guru
> Mike Irwin has been known to suffer sleepless nights laboriously 
> selecting
> cells for his creations...
>
> H^) harry  (or was that 'sheepless' nights ???  :^)
>
> Paul Higgins wrote:
>
>> Well, you _can_ make optocouplers yourself with a little heatshrink
>> tubing and maybe some black paint, but they won't have the same
>> consistent level of performance that you could get in the commercially
>> made ones.  It depends what you're using them for.  I think for audio
>> switches (as in Mesa/Boogie amps), you can be pretty sloppy with how
>> well they're made.  For compressors, Mutron III clones, etc., you're
>> going to be doing some precision matching, I'm sure.


Paul Higgins
email: higg0008 at tc.umn.edu