There is not much to say
to this, a S&H is frequently used to create random voltages, or to
sample LFOs resulting in repeating voltage patterns. When constructing
this take care to deflux the board. The S&H can handle the "full" +/-10V
scale. Operation is very simple, when the Gate of the FET is at -15 the
FET is completely off. Thus no current can flow out of the capacitor (exept
some leakage). When the Gate is turned towards +15V the FET is turned on
and can charge the capacitor to the input voltage.
The circuit on the right converts 5V
triggers to the +/-15V triggers needed by the S&H
Jörgen Bergfors has pointed out that with a BF245A and the gate resistor R1 is
altered to 47k, the circuit can reach -10V input. (Which isn't always the case in the above version.)
Yet another Sample and Hold