[sdiy] Synth Keyboards and chemical switching

[Mike]

> that is an interesting point . as far as I know in the mid 1960's some
> of the Eocs people ( Electronic Organ Construction society ) tried using
> car anti freeze to give a controlled attack to the keyboard switching.
> this did seem to work but had problems if you wanted to move the
> keyboard, and also when one of the owners tried to buy some Anti freeze
> in summer !

I found a reference to this in a 1960's series of organ building articles in
'Practical Electronics'. I tried it for a friend, though we only built a 1
octave model. The keys all had a set of carbon rods that dipped into
ethylene glycol contained in millings in a perspex block. Version one had to
have wires to the bottom of the keys. Version two had two rods per 'bus' on
each key and two millings. Very long winded and time consuming.

Also of the same vintage, though more useful: I did an optical swell pedal,
using a lamp and photocell, and an optical tremolo based on lamp and
photocell, with a fixed piece of polarised film over the cell, and a
rotating polarised disc, on a variable speed motar. This gave a lovely
sinusoidal volume variation, and by adding a second lamp and cell, displaced
by 90 degrees from the first, a wonderfully smooth pan effect.

On the subject of optical shutter keying, I did some of that too. there is a
long term snag to be aware of: dust!

I seem to remember a variable reluctance key system, a capacitance one
(perhaps used by Compton or Thomas organs), and a sort of  transformer
coupled idea, where the key pushed a core into a a pair of windings.

There was a  book by a UK author called Alan Douglas, (not to be confused
with the famous recording engineer of the same name), which had some of
these detail, I think, though I'm not certain, that he might have written
the articles too.

Mike