White Noise + Sample & Hold module

here’s mine Kosmo format of a S&H from René Schmitz
(with LF398 chip)

“YASH” S&H :

sample and hold

White Noise :

link : https://www.schmitzbits.de/sah.html

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Ha, I discovered this post after replying to @devicex in the Mail Day Thread

@Dud Yep in essence I build the same thing (as I wrote here earlier:
Mail Day Thread ) You may want to have a look at the way I connected the capacitors to the LF, I used IC sockets, so that I can easily experiment with other types.

Here is an updated version of the schematic:

and here is a picture of my implementation:

As you can see in the schematic I left out the oscillator from the original schematic so my version depends on an outside source for triggering. Initially I had also not included the gating bit (the 4093 logic) to the circuit, I thought I could do this by using an external trigger, but the LF398 needs a very short pulse (a few micro seconds) which I had no source for, so I added this eventually which is why it is on a separate strip board.

So far I’ve used it with rather frequent triggers, and not noticed any drop in the output voltage between those which could affect the circuit that follows the S&H. I tried it with an oscillator frequency for a while given that the human ear is very sensitive to pitch changes and could not detect any whining / sinking of the pitch, so to speak.

Your and probably my mileage may vary with long periods between the pulses. So the IC socket approach may turn out to come in handy when the need arises to change the capacitors / experiment with other type capacitors.

Because I wanted to see when the output voltage is either positive or negative I’ve added 2 transistors that will each light an LED. Of course this is a rather course way of indicating the output voltage but it is a FUN way !

Luckily nowadays it is not so much a problem than it used to be to talk about these matters, but I just like lots and lots of flashing lights in my modules!

The attenuator potmeter drawn in the schematic near the Vout leads I ended up not adding to the module, I decided to make a separate general purpose attenuator module for that.

Best practice with CMOS chips: if you are going to build this circuit, do not forget to give the inputs of the 4093 gates that are not in use a fixed value, e.g. ground them. Otherwise the unused ports can lead to oscillations which may affect this or other circuits.

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while going over my notes I remembered this:

I had to add a 1k resistor to the output of the LF398, otherwise I could not use it with some of my synths. Without it the S&H seemed to loose its output voltage very quickly, which should not depend on its load and which is odd as it is supposed to have a low output resistance. And although I do not understand what was happening here, a 1kOhm resistor resolved the issue.

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What devices did you connect it to? As you say, it has a very low output impedance, but the specifications use a 10k load and the short circuit currents are only a few milliamps at room temperature, so the source/sink capacity is probably rather limited. Still sounds a bit strange that adding 1k would save the day, unless the thing you connected it to had a very low input impedance…

I connected it to a few inputs of a Behringer Neutron, Model D and a Crave. With some the response was as I had imagined, with some it was as described earlier. I’m afraid I didn’t write down which inputs were problematic. The 1k resistor resolved the matter.

I will keep an eye on its behaviour as I start using it.

Edit: I remember that at one point I started doubting that the input of the synth was in working order, but I got it to work without a glitch with a signal from another CV source. But as I said, I’ll keep an eye on it.

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Yes, Discourse, I know this is an old topic! But see, I wanted to ask @Dud about it because I’m considering building this S&H. I was going to ask him if he could recall why he changed the value of the integrating capacitor. And exactly how his track and hold switch was connected. Okay, Discourse? Can I do that?

Also, if I’m not completely confused, the 4093 is used only with both inputs tied together, so that makes it just a Schmitt inverter, right? So could a 40106 be used instead? Or is there something extra special about doing it with the 4093?

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Yes it’s old subject, one of my 1st module, now i don’t always know what i’m doing, so …

I had seen information on a forum about the track & hold, the switch is mounted to cut the cap of 470pf.

for the 2.2nf instead of the 1nf ? surely on the same forum, i don’t know.

but I have to come back to it, it never really worked well, it seems that all the pulses (trigger) are not counted.

the value of the cap? Did I use a polystyren cap? polypropylen ?

sorry for such poor information, but @Jos built it too

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There is one way to find out: don’t be afraid to try it!

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Found this:

DGTom: if you put a SPST ON-OFF switch across the 470 pF cap of Rene’s YASH, you can switch between S&H and T&H modes.

Nothing there about 2.2 nF though.

And then this:

But I’m getting extreme droop in the output voltage no matter what caps I’ve used (many different 1nf caps as well as various other sizes). The best I’ve got was from a 2.2nf cap but that had pretty solid hold, but only gave me about 1-2 volts output even using a 10vpp lfo as the sample source.

but that’s not exactly a ringing endorsement of 2.2 nF.

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yes, i think the better is to follow the René Schmitz original schem, or try …

btw someone would have a source to buy a 1nf polystiren capacitor plz ?

On René’s site it says

Polystyrene caps are now difficult to source, so a polypropylene (PP), polycarbonate (PC) or polyphenylene sulfide (PPS) cap can be used instead.

and coincidentally I just got some 1 nF PPs from DigiKey a couple days ago.

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i’ve just find this one

https://www.musikding.de/Styroflex-capacitor-1nF

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