Mixturtrautonium (more details)

[Dr. Jörg Schmitz]

Regarding the "Keyboard" from the Mixturtrautonium :
(By the way : it is called "Bandmanual")

The string :

I used a thin (15 Ohm/meter) isolated Konstantan-wire. 
This was winded around a string (used vor a cello, normally).
After winding, the wire was grinded, so that the 
surface of the string behaves like a pot.
The String (St) is fixed 1 cm above a 70*3 cm sheet-steel, 
which is polished. 

The rest  :

The sheet-steel(SS) with the string is fixed on a linkage
(aluminium) with the SS on one side and two ball-bearings
(BB) to provide soft movements.
Below the SS, two springs are fixed, so the SS moves down
while pressing the string, corresponding to the players
finger-pressure.
The whole "keyboard" is fixed with the Ball bearings at 4 cm 
height over the ground plate.


 BB+-----------------------------------------------------+BB
   |                                                     |
   |(+)                |->V                           (-)|
   +-|-----------------+-------------------------------|-+
   | +------------------------------------(St)---------+ |(SS)
   +-----------------------------------------------------+

A current source on both ends of the resistor-string will
lead to a specific Voltage on the sheet-steel while
pressing down the string on a special position (presupposed
an adequate interface behind the sheet-steel).

This is a bit similar to the design of a monophonic 
analog synth keyboard.


As I mentioned, the original mixturtrautonium additionally 
has some kind of aftertouch. In Oskar Salas instrument, 
he uses Glycerine-resistors (connected to the SS and the
ground plate using a mechanical device) to get a voltage
corresponding to the pressure (the mechanical device "dives"
into the glycerine, corresponding to the pressure).
This was too complicated, i use a simple photoresistor
and a led on the ground plate, between them a little black
paper-strip fixed on the movable part.
The resulting voltage is used for vca-modulation in the
Mixturtrautonium, but it can modulate anything
else having a CV-input.

My "Bandmanual" has two devices, one for bass, one for
melody.

I'm still working on it, there are some details missing :

for example, 0.5 cm above the string, there are small metal 
stripes, 5 for each octave, which presses the string down
on a fixed position. This will help to find most of the
notes quickly. But : the most interesting thing in playing
this instrument is using the portamento-effect by pressing
the string down and "gliding" up and down. Of course,
then you have to press the string BELOW the metal stripes
when playing the first note.

One ramaining problem:
I don't have any idea of who to build a subharmonic 
oscilator with 1/2,1/3,1/4 ... and/or 1/24th freq of the 
master oscillator, generating sawtooth waves, all with the 
same amplitude. 
My only idea is using a microprocessor, but
Oskar Sala build his instrument in the 30th, with tubes
(Surely without microprocessor).
Any ideas ????????????????????????????????????????????

Jörg



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