[sdiy] trying to understand appregiators in late 70's synths

[Dave Manley]

Florian Anwander wrote:
> Hi Dan
> 
>> forgive for being an idiot, but how can i incorporate this into an 
>> arppregiator?
> Yep. your doubts aren't wrong. This keyboard is only the first step, but
> it delivers a key as digital 6-bit word. This has to be 'postproduced'
> somehow.
> 
>> due to my lack of german...is it a mono keyboard?
> Hmm, yes and no. If you'd put a D/A direct behind the Latch then it
> would be monophonic and would always send the highest note.
> 
> But one might add further logic to make it polyphonic and need this for
> the arpeggiator too. I am only brainstorming (as far as there is any
> brain to storm inside my old head ;-)) to the mail client now...: e.g.
> for eight voices you need eight latches. The trigger from the 4051 must
> be advanced with each new pressed note to the next latch. But then I am
> not sure how to act on, if more than eight keys are pressed.
> 

Years and years ago, there was a Paia keyboard scanner circuit that you 
could use as a simple arpeggiator (IIRC) by controlling the scan clock. 
Normally, the scan clock was running so the entire keyboard was being 
scanned every ~1 ms.  In this mode the scan clock was stopped when a 
depressed key was found, and then re-enabled based on the arppegiator 
rate.  As it scanned the keyboard from low to high, it would output the 
digital code for each currently depressed key, pause, and then go to the 
next key.  It looks like the elektor circuit could probably do the same 
with some mods.  If you get a little clever, you could probably change 
the direction of scanning for up or down arpeggios (and if really clever 
up/down or random).  I think this was described in one of John 
Simonton's lab notes when he started introducing the digital 
keyboard/computer/quash/etc.

-Dave