[sdiy] Multi-voice architecture without CV parameters: mechanical replication of settings?

[ChristianH]

For a minute I thought I was back in the early 70s, when people
really considered crude and awkward mechanical stuff like that to be
practical... 
Except back then it sometimes was the only way to do things at all.

Chris



On Sat, 3 Apr 2010 14:45:05 +0200 cheater cheater <cheater00 at gmail.com>
wrote:

> Hi guys,
> I was recently considering older synthesizers, such as the SEM, and
> also other designs where a lot of the settings are not
> voltage-controlled. One problem many people mention is having toturn 8
> knobs (in an 8-voice system) to change one sound parameter.
> 
> I was wondering what ideas you guys had for solving this problem?
> 
> The obvious way of having one 'knob' control multiple resistances is
> to have a multigang potentiometer. However these aren't very popular:
> even 2-gang potentiometers can be difficult to find for some
> resistances/transfer functions.
> 
> One other way to do this is to have separate potentiometers arranged
> around a worm drive (if someone doesn't know what I'm refering to,
> have a quick look here: http://en.wikipedia.org/wiki/Worm_drive ). You
> could have one long worm shaft (the screw-like gear) connected to
> multiple potentiometers with cogs on their shafts, instead of knobs.
> 
> Of course this has its own problems:
> 
> - the worm drive has to be precisely placed so that the axis of
> rotation is in the right distance to the axis of each of the 'worm
> wheels', i.e. the gears fixated on the pots. If the worm drive shaft
> is not perfect (it is slightly bowed) or the axis is a bit off(and
> hence not equally distant to the axes of the pot gears), a pot gear
> could have less contact with it and presumably start skipping; This
> can be helped by using a spring to press the pot's gear against the
> worm gear, but that could lower the life of the system, especially the
> shaft of the potentiometer which is not built for constant force
> applied perpendicularly to its axis of rotation.
> 
> - the worm drive will inevitably have a ratio lower than 1, which
> means the knob will be multi-turn and hence 'slower' than normally.
> Some people might not like that
> - more force has to be used to turn the knob
> - mechanically difficult assembly which makes it expensive
> 
> Another way is to use a cam shaft drive like the hammond novachord.
> You can see on youtube (I cannot use it right now so can't find the
> exact link) a demonstration of how its 'brightness' knob works.
> 
> Another way would be to make your own multi-gang potentiometers. I
> guess in a typical potentiometer the shaft could go through a hole in
> the resistive element and out the back. I guess you could make such
> potentiometers without a shaft, but with a keyed hole for receiving
> the shaft; then you could take one long shaft and just line up as many
> potentiometers on it as you wanted. Sound like a good idea? I wonder
> if any currently existing potentiometers could be modified for that.
> 
> Of course all multi-potentiometer setups inevitably have the issue of
> differences in resistance at a given position; but this isn't an issue
> of concern if you're taking this approach; you can accept this as a
> way of making the sound 'more lively'.
> 
> Thoughts? :-)
> D.