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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lm386 – projects

I just got a batch of lm386 audio amplifying ic’s. I’m pretty stoked about it. Mostly because they were super cheap and I have seen them included in many applications.

Despite what you will read on many electronics forums, there are quite a few projects that you could use the lm386 for. So, I wanted to include some of them.

First off, here is one place you can find the datasheet for the lm386:
lm386 datasheet

Here is the pinout for the lm386:
lm386 pinout diagram

Interesting project #1
lm386 smashdrive distortion pedal
This looks simple enough to build and has a few options for modification.

Interesting project #2
Using the lm386 as an oscilator
This step by step shows how you can produce a square wave from the lm386. This is a good way (and cheaper?) to do something other than going the common 555 route.

Interesting project #3
DIY Tremolo Effects Pedal Schematic Using lm386
In this example, the author uses a lm386 as an amplifier and then oscillates the power of the audio amp with a 555 timer IC. However, you could use the second interesting project to create the oscillator using another lm386.

Here a link to the original article:
DIY Tremolo Effects Pedal Schematic Using lm386 and a 555 timer

Conclusion:
Although the experts will say things like “don’t bother with the noisy little lm386 audio amplifier” or “the lm386 isn’t an op-amp it’s an audio amplifier! There are some many better suited IC’s” or whatever, we can clearly see that there are many things that the beginner can do with a handful of them.

One could easily create an simple syth with an lm386 generating a square wave as the primary voice. With a little effort, another lm386 oscillator could be made to modulate the volume (i.e. Tremolo) or the pitch (i don’t know what that’s called). Finally, everything could be distorted through a distortion circuit and amplified to a little speaker or headphone jack.

Good luck!!!