AW: Re: [AH] building an analog keyboard controller for a

[Ingo Debus]

Haible Juergen wrote:
> 
> a keyboard with a series string of trimpots for tuning each note
> individually.
> To make things worse, tuning one note would change the tuning of all
> notes above (or below?) this one as well.

:-) like the Tuenker "Sound Organ" I built in 1974 or so. This wasn't
even voltage controlled, the trimpot string was just the R of an
oscillator. When no key was pressed, the oscillator didn't oscillate. I
soldered the trimpots *under* the keyboard, so I had to remove the whole
keyboard when I wanted to tune the instrument. Later I tried to reach
the trimpots with a long piece of thick wire, filed like a screwdriver
at one end.
And of course I used the cheapest trimpots I could get...

But it didn't come to my mind that this was a bad design those days
(being 15 years old, I couldn't tell a good design from a bad one of
course...). Electronic organs of these days had to be tuned too, only
one  octave, but nevertheless...

Later (1975) Tuenker published another book describing a true
synthesizer. It had a linear VCO and a keyboard with a trimpot string.
Quote: "...the exponential contacts [of the keyboard, the trimpots]
replace the often quite unstable exponential function generator...".
There's another set of keyboard contacts with a string of equal metal
film resistors too, to control extarnal expo VCOs. Maybe Tuenker - like
the people at ELO - didn't know about the Korg circuit? Or is it a
patent infringement to publish a DIY circuit using a patent?

>From when was that ELO circuit? Was it before or after the Formant (1977)?


> when I'm raving against trimpots

yes, trimpots in analog circuits are much like monoflops in digital
circuits... there's a German word for it: "Pfusch"... ;-)

Ingo