Random White Noise / Sample and Hold Circuit (part 1)

INTRO

I found this great book called IC Op-Amp Cookbook.
ic op-amp cook book by Walter G. Jung

The book is great because it goes through the “what is an op-amp?” and it goes through the “how does an op-amp work?” then it goes through the equations (which I don’t get AT ALL!) and the it has tons of examples of Op-Amp applications.

One that I found very interesting was the “sample and hold circuit”.
Basiclly, it takes the current voltage at it’s input at a particular interval (determined by either a switch or a clock pulse) and holds that voltage for a period of time. Now, the input could be anything. A sine wave, triangle wave, or… dun dun dun dun… WHITE NOISE!

Naturally, I instantly saw how this could be applied (or at least how I wanted to apply it). I wanted to have the output from the S/H (sample and hold circuit) drive the frequency of an oscillator.

If I could figure out a way to control how far apart and how tight or loose the Sample and Hold circuit operated then you could create some really cool effects. Totally random beeps, blips, and boops. Or tightly controlled variations on the signal I was modulating.

GREAT! Now, how do I do it!?

White Noise Generator with a single 9v supply

I found some great schematics on the net, of course. Music From Outer Space has some excellent stuff. Including, schematics that include both the white noise generator and the sample and hold circuit.

But it looked a little too much for me. Plus, a lot of the schematics have both positive and negative voltages. I don’t like that. Why? Because I’m lazy.

I started off trying to find a schematic for a white noise generator with only one 9V supply. Not that easy. But I did end up finding one that would work with the LM324 quad op-amp.

Yesterday, I bread boarded that baby up and it worked! First try too!!!

LM324 quad op-amp white noise generator
LM324 Quad Op-Amp White Noise Generator
An audio noise generator capable of driving earphones or small speakers

I was chatting on www.electro-tech-online.com/ and audioguru said this…

The lousy old LM324 has such a poor high frequency response that the two in series, each with a voltage gain of 50 in that circuit will cut high frequencies at the output above only 5kHz. Audio goes up to 20kHz so two octaves are missing.

Take it or leave it. But it worked. And first try! So, it’s a winner in my book. Only once I get it hooked up to a Sample and Hold will we know for sure it it is as good as I want it to be.

Today I found anouther one that works with just one LM386 audio amplifier. It looks even simpler! But I haven’t built it yet.

White Noise Generator using the LM386

link

There are many more complicated schematics but these are the simple ones that I have found.

NEXT:
Random White Noise / Sample and Hold Circuit (part 2)
The Sample and Hold Circuit

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10 thoughts on “Random White Noise / Sample and Hold Circuit (part 1)

    • Sorry it took so long to get back to you. I haven’t done anything with my blog in ages.

      The sample and hold circuit was the original idea. I wanted a simple white noise generator and a simple sample and hold circuit to get the cool pseudo-analogue beeps and boops sounds you get with the classic sample and hold.

      In theory, it should work. the white noise generator isn’t’ as robust (if I understand correctly) as a pink noise generator so you might only get a few notes out of it. But I’m not totally sure.

      I never got it working though.

      Were you able to come up with anything? I would love to see your project.

      Cheers!

  1. Thank you so much. I’ve been needing a simple white noise generator for a project and all the ones I could find were the two transistor 12v requiring ones. This one used parts I had laying around, thank you.

  2. Hey, thanks for posting this! I just used the second white noise generator schematic on this page for my first homemade noise maker. It is very loud (need to add volume control knob if you want to use it outputted to like a guitar amp or audio interface) and the pots in the circuit give it a good range of timbres.

      • It might be. I don’t think they are the best amps… but I don’t have tons of experience with them. there is probably much better circuits out there.

        Thanks for posting!

  3. I have built also the second circuit, but the noise it makes is not high. I have to put my ear touching the speaker to listen to a little white noise :S . any advice that I can say?

    • Amplify it.
      You can pick up op-amps and audio amps at radio shack or eBay for super cheap.run the output to the amp and then into a speaker or whatever.
      I would start there.

      Let me know how it goes.
      Thanks for the question.

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