[sdiy] Minimoog non-linear keyboard response

Oren Leavitt obl64 at ix.netcom.com
Thu Jul 23 07:16:05 CEST 2015

On 7/22/2015 11:15 PM, Eric Frampton wrote:
> …or “unevenly exponential” might be a better way to put it.
> If I can get the A’s on each end of the keyboard to scale up perfectly for each oscillator, and I can get the octaves on all three oscillators to switch evenly, what would cause the internal intervals between those A’s to not be linear? In other words, if A1 and A4 are correct, A2 might be a little sharp and A3 might be a little flat, but it’s enough of a deviation that when switching octaves, the oscillators don’t stay in tune with each other.
> The same situation happens whatever octave it’s in - the keyboard itself seems to be triggering non-linearly (non-exponentially) internally, no matter where the tuning on a given oscillator is set. If the ends are right, the middle is wrong.
> I’ve got a buffer board installed, so I don’t think it’s that.
> Thoughts? Time for new resistors on the actual pratt-read assembly? Or was this what the field service mod on the keyboard PCB was supposed to solve?
> e

Most likely the keyboard resistor divider. Measure the voltages (or the 
resistance) from the low end of the divider to various points on the 
divider and see if the same pattern appears in your readings.

- Oren

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