[sdiy] sample and (infinite) hold

[RMC]

>> Has anyone built a sample and infinite hold and can shed some light
>> in my direction?

polystyrene caps are the right sort and indeed, construction methods play a 
large part in minimising leakage currents.

Take a look at how some oscilloscope circuits are constructed:

1) mill a slot around the critical components so that the slot cuts right 
through the board

2) No copper on the opposite face

3) Use "lands" made from PTFE - Tektronix used small PTFE "studs" which push 
into the FR4 fibreglass board. The stud contains a solder well, into which 
you solder the components.

4) Build the circuit in a "skeleton" style using such lands, so the critical 
components are hanging in the air.

People like bob Pease at Natsemi wrote datasheets on this kind of 
technique - worth looking for  on their website.

Cheers

RMC, England