[sdiy] MS-20 tempco (was Model D service)

[Tony Kalomiris]

Hz/V is a pitch/ per volt relationship, not a linear / exp relationship.
In the MS-20, it's set to 21mV/oct (instead of the 18mV/oct) in standard 1v/oct.
1 volt input change will produce an octave + 2 semitones, according to my notes.
If you wanted to make it standard 1v/oct ,you would need:

1) replace 110K Rf (R39) with 2K Tempco , ideally, epoxied to the '1583.
2) replace 5.11 K , R40 with 100 ohm MT trimmer is series with 390 ohm precision or 1 % resistor, output at the wiper to exponential converter bases.

This makes the output 20 mV/ oct which can be brought to 18 mv/oct with the trimmer.
This is for the VCO1+2 input (if you were MIDI to CV'ing you would use this)
Incidentally, the nice thing about CV'ing this way is you can use the keyboard to transpose live! (just pin down a note as the sample and hold droop wil affect pitch, unless you want that effect;)
Yes the keyboard is exponential to the linear response input. The modulation is applied to the exponential input. 

On 2017-05-08, at 10:30 PM, Adam Inglis wrote:

> Hz - per - volt synths don’t need tempcos, do they?
> 
> I have no experience with the MS-20 but I do have a Korg 700 from a few years earlier. It never needs re-tuning.
>