[sdiy] rwilson sample hold HELP

[Rutger Vlek]

Dear Jim,

I've built it on a 15V power supply. I had the same problems as you have. 
The circuit is very very sensitive to static, so when you touch the FET with 
your hand it's enough to trigger it.

About the clock, I had the same problem too. After alot of searching I found 
out that I incorrectly calculated between uF and nF. The capacitor for the 
clock was about 100 times off, so the clock speed was enormously fast. Find 
out if this is your problem. Also find out what happens to the trigger 
output when you turn the speed knob.

You have to realise that the pulses from the clock are about the length of 
20ms so they can not be seen on a normal multimeter. The only way you can 
see that something is happening with the clock is that if you speed up the 
pulses with the knob your average voltage should rise a little bit at the 
trigger output or pin 1 of the IC. That way you can verify if your clock is 
working. It it's not working you should check a couple of things....

Did you make the connection to the pot correctly with the resistor across 
the pins and does your board have the 15V it needs? If that's all ok you 
should check the switching transistor (that's Q2), perhaps replace it with 
another one if it might be damaged by static or something.

If your clock is working you could take a look at the trigger mechanisme. 
Note: I had to make the modification that Ray indicates in his schematic 
with blue on the right side for the triggering to work. This gave me another 
problem though: if the input gets below -6V the input can trigger the 'hold' 
instead of the clock. This problem could also be solved, but was not 
nescessary for me since I took all the signals that could be going in below 
the gain that causes -6V to happen.

Well, hope this helps. After you get it working you probably find out that 
the scaling is way of. I also did modifications on that part...so get back 
to me when you need it.

Greetings,

Rutger


>From: Jim Bob <c10h14no2i at yahoo.com>
>To: synth-diy at dropmix.xs4all.nl
>Subject: [sdiy] rwilson sample hold HELP
>Date: Fri, 3 Feb 2006 14:57:53 -0800 (PST)
>
>Ok.. so earlier I asked about the transistors in the sample hold I  built.  
>Someone said raidioshack had the correct ones, so I went,  and they did.
>   I...
>   Etched a new PCB.. checked it over very carefully
>   soldered the parts on one at a time checking the connection and for any  
>stray solder traces.  (these are all new parts.. didn't take any  off the 
>old board)
>   Used the correct transistors
>
>   I have the EXACT same problem!!
>   It is like the clock is not working, or something.  If I tap the  
>transistor leads it samples and holds.. each time I tap it, I get  another 
>sample.   Anyone have any ideas?
>
>   Has anyone else built this sample hold?  Anyone running off 15 volts?
>
>   
>http://www.musicfromouterspace.com/analogsynth/singlechipsampleandhold/singlechipsampleandhold.html
>
>   thanks for any help
>
>
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