[sdiy] Minimoog non-linear keyboard response

Michael E Caloroso mec.forumreader at gmail.com
Fri Jul 24 03:08:25 CEST 2015


Keep in mind that the keyboard CV is NOT 1v/oct.  It is 1.02v/oct.

The voltage across each resistor in the keyboard should measure the same.

Wouldn't hurt to look for evidence of a liquid spill.  Beer or soda is
not kind on circuits.

MC

On 7/23/15, Oren Leavitt <obl64 at ix.netcom.com> wrote:
>
>
> 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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