[sdiy] sample and (infinite) hold

[James Patchell]

Of the capacitors you listed, polystyrene is probably the best for a sample 
and hold, although, this has nothing really to do with droop.  For an 
accurate sample and hold you also need a low dissipation factor 
capacitor.  Droop is caused by other components, like your switch and 
buffer amplifier and circuit board leakage...oh yes, your PC board must be 
spotless clean to get the best droop performance.


At 02:29 PM 1/5/2005 -0700, Scott Juskiw wrote:
>>Infinite is a really long time...
>>
>>I've worked with some of that stuff,  and it's crucial that you follow the
>>right construction practices there,  and that you choose the proper type of
>>capacitor for your hold.
>>
>>What kind of a cap did you use?
>>
>>The stuff I built,  I used a dual FET as was done in something or other I ran
>>into at the time (ARP?  I forget),  but that was before FET-input op amps
>>became commonplace.  I don't know if they'd work or not,  but the use of them
>>seems to be pretty common.
>>
>>What kind of droop are you seeing and in what kind of a time frame?
>
>I'm using a polypropylene at the momen., I've tried polycarbonate, 
>polystyrene, they all droop eventually. The S&H output is fed to a 
>quantizer which sets the root key of a repeating sequence. After a minute 
>or so the output will droop so that the quantizer will knock the sequence 
>down a semitone. I'd like the sequence to stay in key for 20 minutes, or 
>20 days, or the full length of a Klaus Schulze piece.

         -Jim
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