[sdiy] minimoog keyboard question

Ian Fritz ijfritz at comcast.net
Tue Jun 23 13:14:38 CEST 2020

Neil --

Since it is a constant offset, it should merely shift your overall VCO pitch a bit. So presumably you can make the correction at your VCO front end.

Another interesting observation I made: We are often told that increasing the sampling cap's value will give longer hold times. That is true if the leakage is from the circuit, eg opamp input bias. But I didn't see any difference in my tests. I believe that internal to the cap itself leakage is an intensive property, ie there is something like a leakage current *density*, so the actual leakage *current*  scales geometrically the same way as the capacitance. Anybody know anything about this?


>> On Jun 23, 2020, at 1:24 AM, Neil Harper <metadata at gmx.com> wrote:
>> On 6/18/20 11:54 PM, Ian Fritz wrote:
>> The S/H on my website gives a droop of about 3 cents/hr. And it can
>> sample up to 10kHz. In agreement with Brian, droop is determined by cap
>> quality.
>> Ian
> thanks ian, i had a look at your schematic already. if i was using it to
> sample an existing 1V/OCT pitch CV, will the resulting 'held' voltage
> come out accurate? i noticed you mention that it could use an additional
> trimming/offset, so it could be dialed it to be accurate in that way?
> thanks for your time and thanks for the clear and simple schematic by
> the way, i'm looking forward to breadboarding this to understand it better.
> --
> /// Neil Harper
> /// Every Wave is New Until it Breaks

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