[sdiy] Vactrol'ed Moog Parametric - or stepped controls?

[Larry Troth]

I'm far from being any kind of expert, but isn't one of the endearing
qualities of analog the "inexactness" of it all?  No two devices ever sound
identical.  IMHO that is a good thing.  I'd like to stick to vactrols and
allow for on-board pots to do any fine tuning if two or more units are being
batched.  Oh, by the way, I'd LOVE voltage control!  Every one of JH's
designs I've gotten, committed to, or will get is becoming part of my
SynthDotCom/MOTM/CGS/Tellun/JH/EFM/diy modular system.  Long Live Voltage
Control!

And yes, I'd buy a board!

Larry T. 

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of JH.
Sent: Tuesday, November 27, 2007 4:11 PM
To: Dave Manley; diy
Subject: [sdiy] Vactrol'ed Moog Parametric - or stepped controls?

>A very good idea, but how well matched are vactrols?  Would there need
>to be a lot of calibration/trimming required?

That's a good question.

Needs a lot more simulations to find out.

My gut feeling is that there wouldn't be much trimming needed (unless you 
need precise labelling of the front panel controls), but we'd need at least 
3 different types of vactrols. It's certainly possible, but needs a lot of 
design work.

An different route to go would be going for ultimate precision, and forget 
about voltage control:
Using rotary switches instead of potentiometers:

You'd get quite a good frequency resolution, using 23-position rotary 
switches that are favored by High End Stereo Amp builders.
For Bandwidth, a 11-position switch is certainly enough. And another 
11-position switch for cut/boost.
The good thing about *this* is that you can even mix the switch and 
potentiometer approach:
Use potentiometers for Frequency and/or Cut/Boost, but a switch for 
bandwidth, if continuous sweeping is important for you.
Or use switches everywhere if precise recall of settings is important to 
you.
Gladly, the one control that is the most tricky to implement with 
potentiometers (the bandwidth), will suffer the least from a stepped 
control, IMO.

JH.

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