[sdiy] minimoog keyboard question

[Ian Fritz]

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

On 6/18/2020 8:33 PM, rsdio at audiobanshee.com wrote:
> How long can the MiniMoog sustain a note with its "contour" after a key is released?
> 
> The Sequential Circuits Pro-One has a drone feature, but it has a digitally scanned keyboard, so that's a DAC driving the voltage.
> 
> S/H droop is reduced by using higher quality capacitors, higher capacitance, and/or higher impedance on the follower stage. It's very specific to the circuit used. That URL doesn't mention the MiniMoog, so the 3 mV/s is completely unrelated. Does the MiniMoog use the LF412?
> 
> I've designed S/H with high-grade WIMA polystyrene caps and JFET followers with impedance in the 10 GΩ range. Those puppies don't droop. Cheaper caps discharge themselves. Glancing at the ARP 2620 keyboard schematic, that circuit uses discrete FET technology - most likely to reduce droop compared to other circuits.
> 
> Brian
> 
> 
> On Jun 18, 2020, at 6:45 PM, Neil Harper wrote:
>> i was playing my be----ger 'model d' yesterday with a midi keyboard, and
>> started thinking about how they keyboard on the original MiniMoog worked.
>>
>> it was basically a string of resistors, one between each key right? What
>> kept the pitch CV constant after you let go of the key?
>>
>> does it use a sample and hold here? the little i know about sample and
>> hold circuits, they all have a "droop" to them.
>> http://mysite.du.edu/~etuttle/electron/elect53.htm says ~3mV/s, which
>> would get pretty noticeably flat after only a few seconds.
>>
>> i had a quick squiz at the schematic but couldn't see or understand the
>> relevant section.
>>
> 
> 
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