[sdiy] ODP: Hammond Aurora Keybeds

[Tom Wiltshire]

Two slightly-more-vintage examples that come to mind are the Sequential Pro-One and the Roland SH-101. Sequential used a "proper" AD558 DAC chip, Roland hacked a cheap DAC using a 4050 buffer and 6-bit binary-weighted resistors into a summing op-amp.

So you can still claim "classic analogue synth" status if you've got a scanned keyboard. It doesn't *have* to be a 1V/oct resistor chain and a droopy Sample-and-Hold!!

Tom

> On 15 May 2025, at 17:40, Roman Sowa via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> Exactly.
> Logic driven keyboards are nothing new. But it's really cheaper and easier to put a micro into the task today. You have to enjoy the beauty of logic design to go that route, and then it becomes timeless classic.
> 
> Examples that come to mind now: not so vintage yet, but MacBeth touch keyboard is just self running, no-program, logic circuit. Or the most advanced one I've seen, the one designed by Dave Rossum - velocity scanning keyboard for Oberheim, with 64us scanning cycle and 12-bit precison velocity sensing. Really massive design with I think 40 ICs in it. Well, the old 4 Voice from Oberheim, also Dave's design, was also a bunch of logic. A counter driving a mux, and when key was pressed, a pulse appeared at the time when counter state was representing the key number.
> Or my keyboard I did in 1990 when I didn't know how microprocessors work at all, very similar idea to 4Voice, only about 15 CMOS 4000 chips. There's a schematics somewhere in the web if anybody interested.
> 
> Roman
> 
> W dniu 2025-05-15 o 17:15, Phillip Gallo pisze:
>> ... and as memory serves, Allen Organ company did just that in the late 1970's, switching to matrixing keyboards in the early 1980's.
>> My first DIY digital keyboard (~1980) was a CMOS counter driving a raft of CD4051 muxes to encode an old Vox Continental clavier.
>> 1st keypress stopped the counter, latched the count value to a CD4050 buffer which drove 6 binary weighted resistor values (the 2 smallest values getting two parallel buffers).
>> This 6 bit  keyboard eliminated years of Sample and Hold frustrations.  A second version switched to CD 4067 mux's to reduce chip count.
>> p
>> On Wed, May 14, 2025 at 11:53 PM Roman via Synth-diy <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
>>    The best what you can do today is scan the keyboard digitally and
>>    use DAC as CV source. No analog keyboard circuitry ever designed
>>    will be comparably reliable. They would have gladly make keyboards
>>    that way back in the 1970's as well but the technology needed was
>>    too expensive.
>>    Roman
>>    ---- Użytkownik drheqx via Synth-diy napisał ----
>>    Hi all,
>>    I have the keybeds and draw bars etc. from a Hammond Aurora organ.
>>    These are not matrix type keybeds. Each key closes a switch to a
>>    common bus.
>>    Is this a good time for me to consider doing a volt
>>    /octave keyboard controller?
>>    I definitely don't want to midify these. That would be a waste.   I
>>    was considering building a voice per key synth because i love these
>>    key beds and it would be so unique, but I'm short on time like so
>>    many of us.
>>    Anyone know of a good kit to make a 1v/ oct controller, maybe with
>>    some added features.
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