[sdiy] vactrol?

[phil macnutt]

 Thanks for all the info from everyone.
Quick question, does the performance (speed, etc) of the vactrol matter much if i am just using them across potentiometers with a preset unit (programmer)?  that is, the values are only changed once when setting up the programmers, then they stay put.  I'm a little out of my knowledge-zone on this, so forgive me if i am not making sense...

phil in austin (where it is 100 degrees every stinkin' day)

On Saturday, August 20, 2005, at 10:33AM, Peter Grenader <peter at buzzclick-music.com> wrote:

>groovyshaman wrote:
>
>>> Anyway, i could use a little help on where to source these devices, and
>> any tips on connecting them.
>
>
>Yeah, they are pricey, but they perform really really well for musical
>applications..so - GET OVER IT (kdding).
>
>The VTL series is made by Perkin-Elmer and available through Allied. As far
>as app notes, go to the Perkin-Elmer site and look under the
>opto-electronics tab, there is a downloadable pdf which will answer all your
>how-to's in this regard.
>
>All Electronics has a bin with some sort of opto-isolated photo resistor in
>them as well.  They are not Perkins and I have no idea of their resistance
>range, nor if they are available in their on-line catalog as much of the
>floor stock is not.  They may sell them if you call - but I'm pretty sure
>the guys won't have an idea what a vactrol is.  If it's any help, they are
>kept in the same isle and right next to their zeners and chokes.
>
>There's also a Canadian firm making vactrol-type devices (the name escapes
>me right now -duh) which I've heard good things about. I want to say
>Soltronix or something along those lines, but I'm pretty sure that's off the
>mark.  Some of these are very fast though (M&K used them as the primary
>ingredient in the limiters within their whiz-bang subwoofer amp which had a
>1/2 cycle response time at a 125 hertz - that's pretty damn fast for a
>photoresistor.). 
>
>There's also a slew of them made in China, which I believe Dieter is using
>in his vactrol devices.  They don't appear to have the same decay time as
>the VTL series, which for me is THE thing with Vacs.  The Chinese variety
>I've seen are rectangular shaped - about a 1/2 inch long by about 1/4 inch
>square.
>
>My feelings - if you don't want a vac to be slow, then don't use one.
>You'll spend less money and take far less space using a trans. amp like the
>3080 or 13700. Remember that not only are vac's as big as june bugs,  you've
>got to drive them and this will require a somewhat linear current or voltage
>source - so we're talking an tranny, or an expo pair, an op amp and a
>trimmer or at very least a divider for the setting the gain.
>
>hope this helps,
>
>- P
>
>
>