Synth-Diy archive, S&H question

[Harry Bissell]

The first fet is a simple analog switch, when the gate is high... it is
closed and the S/H cap gets charged to whatever the input level is. When it
goes low, the switch is open and the voltage stored on the cap has nowhere
to go.

The second fet is a buffer so the cap charge doesn't leak. It will
eventually droop, but probably not before the next sample.

Yes a triangle will give a stepped triangle, but maybe different each time
if the clock is not synced to the triangle... Plug in an analog noise source
for random... it might help to low pass filter the noise (and amplify it to
recover the lost gain) source first.

Hope this helps...

H^) harry

--M wrote:

>     Hey all I had some questions about sample and hold and thought I may
> be able to find some answers in the synth-DIY archive but I can't seem
> to find it.  Any pointers?
>
>     Specifically I was looking at Tom's LFO5a, it has what appears to be
> a very simple S & H circuit built from 2 J-fets, but I don't know why
> and how it works.  What sort of signal does the S&H *in* expect?  In
> commercial synths with hardwired signals, what do they feed the S&H in?
> How is the randomness generated?  That is, I see the clock *in*
> selecting what point on the incoming wave to sample from, but if you
> feed it a triangle wave, say, then wouldn't it just be a stepped
> triangle at the output?