[sdiy] Single Chip Sample & Hold not working [Music From Outter Space]

[Rutger Vlek]

Hello everyone,

i'm currently building the Single Chip S&H from Music From Outter Space 
(http://www.musicfromouterspace.com/analogsynth/singlechipsampleandhold/singlechipsampleandhold.html) 
and got it running, but it's not really working the way it's meant to. I 
hope someone could point out what's going wrong.

I entirely followed the schematic on the website, with the only difference 
that I used 2 2N5486 N-Fet's. I did NOT make the D1 modification you state 
on the website since i don't know if this is nescessary for the 2N5486. 
Another small change is that i used a 3M3 instead of a 3M resistor across 
pin 1 and 3 of the sample rate pot. I connected 15V to the wiper of the pot 
(pin 2) and the signal going into the S&H to pin 1. I left pin 3 
unconnected, but it is in a way through the 3M3 resistor...is that correct?

The problem is as follows:
The Sample Rate knob goes from very fast to extremely fast, making the 
Sample and Hold sound more like a LAG generator then a S&H. Another thing is 
that the voltage is not really held at the same level. It drifts a bit 
towards the voltage that the input actually is getting at the moment... 
That's a bit strange too... It sounds like a Sample & Lag now.

I'm using the S&H with Oakley modules and I run it on +/-15V. I tried 
feeding a triangular wave from an LFO to the input and patched the output to 
a VCO's exponential frequency modulation input. I also tried feeding the cv 
from the modwheel to the S&H but this doesn't do anything. I expected the 
S&H to hold the wheels CV for a short period, so when i move it fast i 
should hear the difference, but it's not. The wheel directly to the VCO 
pitch works fine though....

Any suggestions for my problem?

Greetings,

Rutger