[sdiy] string machine technology?

[Antti PitkXmXki]

>From: sasami at hotkey.net.au (Ken Stone)

>It is common organ practice to generate saw waves simply by adding the
>successive sub-octaves via a binary weighted mixer.
>The "down side" of this is that the higher octaves have fewer steps in 
>their
>waveform, rught up to the top octave at the highest fottage, which is a 1
>step waveform, i.e. a square wave.
>
>One way to get the hollow sounding wave shape is to use a 1:4 ratio in your
>division. i.e. skip an octave when you mix the steps.

Thanks for the information you all, interesting stuff. That Korg PE-1000 
sure seems very interesting. I've got a project Crumar Multiman S, it needs 
cleaning and fixing of some switches, and it has a problem that the volume 
of the string sound is very low. It propably wouldn't be that a difficult 
project, but there's so much other stuff to do...

I recommend for those who are interested in this subject to check out the 
schematics of a Farfisa Compact organ. It's got two germanium transistors on 
each of its dividers, but they are connected completely differently than the 
usual binary divider, and they result in that unique 
"pulse-sawtooth"-waveform (only the highest footage on the highest octave 
uses squarewaves - I guess because of the high pitch, it's not very easy to 
hear any difference in waveform content). They must be sort of independent 
oscillators that are hard-synced, because each oscillator card has different 
values on all the divider capacitors. The final waveforms look kinda 
different than the divider waveforms, so the organ might not just filter the 
waveforms but add other octaves to them as well, like some squarewave organs 
do to get semi-sawtooth waveforms (however, I'm not 100% sure). Too bad the 
schematics are kinda messy and it's difficult to figure out exactly what 
happens in the electronics of the organ.

Antti P.

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