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

[cheater cheater]

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.