[sdiy] Linearized Vactrol?

[Thomas P. Gootee]

Hello, everyone.

I am new to this list.  My name is Tom Gootee.  I live in
southwestern Indiana, in the USA.

I was an EE, originally, until 1984, then did mostly
C-language software for about 15 years, and have been
designing (and manufacturing & selling) analog electronic
systems for the last ten years or so (mostly
test-and-measurement equipment).

I hope that my question is not perceived as too unusual, or
inappropriate, for this group. If so, I apologize.  But I
don't know of anyplace else where Vactrols are discussed as
frequently, or by people whom I respect as much as the
members of this group.

-----

I am wondering whether or not there might be any interest in
a wide-range, 'perfectly'-linearized voltage-controlled
Vactrol-type device (i.e. a wide-range linear
voltage-controlled resistance).

I have developed a circuit that does that, which would also
work for any other LED/LDR type of device (e.g. Silonex, et
al).  I'm just not sure what to do with it.  i.e.  Would it
be worth trying to commercialize it?  Would there be enough
interest?  Would it be foolish of me to simply 'donate' the
circuit into the public domain?

I originally wanted to develop it for use in some of my
(non-audio) product designs.  And I also have audio hobbies,
and wanted a series/shunt LED/LDR-based audio attenuator
with precisely-constant input impedance.

But, for many applications, the vactrol-type devices are way
too slow.  So the applicability of a linearized version
seems somewhat limited.

Also, I think that there are probably other,
somewhat-similar circuits already available, having seen the
(fairly horrible) attempt at it that's published on the
Silonex website.  So it's probably not unique, or even new. 
However, my circuit HAS been structured for optimization of
things like maximum resistance-command step-response slew
rate, with near-zero overshoot, maximally-wide resistance
range for a given LED/LDR device, high precision in general,
etc etc, yada yada yada.

But, since it relies on an identical LED/LDR device for its
control mechanism, any mis-matches (other than a constant
resistance offset) between the target LDR device and the
control LDR device will negatively affect its accuracy.  

In other words, I guess I'm also thinking that maybe it's
really just not all that great, and I might be worrying
about all of this for no good reason.

So I'm hoping that someone here will be kind-enough to give
their opinion about whether or not it's worth pursuing
further, in any way at all.

I'm sorry to have 'blathered-on', for so long, about all of
that.

[P.S.  If anyone wants a fairly-detailed LTspice model of
the Perkin-Elmer/Vactec VTL5C2 Vactrol, or a model of the
Silonex NSL-32SR2, just let me know.] 

Thank you.

Regards,

Tom

Tom Gootee
tomg at fullnet.com
http://www.fullnet.com/~tomg/index.html