[sdiy] sample and (infinite) hold

[Scott Juskiw]

>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.