[sdiy] minimoog keyboard question

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sat Jun 20 05:16:49 CEST 2020

On Jun 19, 2020, at 2:47 PM, Neil Harper <metadata at gmx.com> wrote:
> seems like one of those things that might be best done digitally,

At one point in time, digital was expensive.
At one point in time, even op-amps (analog computers) were expensive.

The problem with analog keyboards is that they're monophonic, unless you create a voice per key. You can get two notes if the circuit is designed for high note and low note, like the ARP 2620, but that's about it.

Eventually, digital scanning of keyboards was so cheap that Sequential Circuits could make an affordable mono synth like the Pro-One using a microcomputer to scan the keyboard. It's not even that they could play chords, but suddenly arpeggiation and sequencing were possible.

Subsequent to massively-popular, cheap synthesizers being able to use digital keyboard scanning on a budget - yeah, digital is best.

> i
> can't see any inherent "magic" coming from these circuits or times when
> a droop would be musically desirable.

It might seem like digital would avoid the need for sample and hold, but you have to think about what it means to dynamically assign keys to voices. You pretty much need S/H to do it right.

As a point of reference, the Prophet VS, which has quite a lot of analog circuits, there are at least 60 sample and hold circuits.

The key to using sample and hold successfully is to refresh the voltage in the cap before it can droop enough to be noticed. The same microprocessor that scans the keyboard can also scan through hundreds of sample and hold channels to update them hundreds of times per second.

> I'm guessing the minimoog reissue
> did it digitally?

The minimoog reissue may have recreated the original keyboard. I noticed a few quirks in the MIDI capabilities that are basically due to the original CV signal path, so Moog may have gone for accuracy rather than what's "best" in general.


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