[sdiy] Interesting article on top octave generators.

[Donald Tillman]

On Dec 27, 2024, at 1:05 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
> 
>> On 27 Dec 2024, at 20:17, Ingo Debus via Synth-diy <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
>> 
>>> Am 27.12.2024 um 08:35 schrieb Donald Tillman <don at till.com <mailto:don at till.com>>:
>>> 
>>> If it was me, I would have directly emulated the chip with, say, 6 CD4040's and some diodes.
>> 
>> That’s what Elektor did in 1974:
>> https://www.elektormagazine.de/magazine/elektor-197411/55706
>> 
>> They used TTL chips, not CMOS. It was quite a huge project. I remember this so well because this was one of the first Elektor issues I bought myself.
> 
> I honestly don't see the point of this type of approach. Discrete dividers has all of the worst features of the TOG chips (locked frequencies, poor frequency tuning, loads of circuit) without the few minor benefits (small size, simplicity, and cheapness).
> 
> IF you'Re willing to throw that much circuitry at the problem, why would you *not* simply build a board with twelve top octave oscillators and then just use dividers from there? I don't get it.

The intent was to be true to the original musical instrument.  It's a repair job, not a redesign job.

But in this case, yeah, I think you're right.  The TOG chips are probably the worst part of the organ, and it would make a lot of sense to replace them with a dozen reasonably stable oscillators with trimmers.

I understand that some large fraction of Hammond X5's have been used as parts sources for the remaining Hammond X5's.

(Does Tim "Organ Donor" Servo have any extra Hammond parts?)

Strategically it would make a lot of sense to build a 12 oscillator board that cables into the IC sockets, sell off the working TOG chip, and then either sell boards to other Hammond X5 hackers, or just publish the schematic, parts list, and Gerber files.

  -- Don
--
Donald Tillman, Palo Alto, California
https://till.com

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