White noise generator

At this sort of current, zeners are pretty white and gaussian, maybe just a tad asymmetric. At much lower currents, shot noise is significant.

The sequence must have been short. A 1 MHz, 64-bit shift register won't repeat in your lifetime.

I think it's "shot", like buckshot falling on the roof.

John

I's suggest two opamps, each with a closed-loop gain of, say 50, to get you up to 100 millivolts RMS, then some sort of power amp to drive the speaker, one of those cheap National thingies maybe. A single opamp might work, ahead of the amp, depending on your numbers... x1000 at 3KHz requires at lease a 3 MHz gain-bandwidth opamp.

John

The opamp noise would probably wind up dominating the resistor noise. That might be OK, but opamp noise tends to be fairly non-white, with a lot of excess low-frequency (1/f) component and occasional pops and other weirdness.

John

Any reverse biased eb junction is noisy like a zener diode. This is white noise... equal energy per hz... you want pink noise? (equal energy per octave)

Yeah, that works. What's the input capacitance on one of those?

John

Tune a cheap FM radio inbetween stations.

I use a 10 Megohm resistor and amplify the f**k out of it with a low noise op-amp.

Graham

Don't semiconductor junctions make excess shot noise though ?

Nat Semi once made a chip that did that. I have a 'little box' I made using one. Sounds horrid. You can hear the pattern.

Graham

p.s. I've sometimes heard shot noise referred to a Schott noise. Any idea which is correct ?

Check out

Also go to Google and put it "white noise circuits", there is a lot of good information there.

Brian

I make 10 Meg = 409 nV / sqrt Hz

Used with a TL07x type op-amp ( 12 nV / sqrt Hz ) it seems to be just fine.

With a bipolar op-amp you would indeed likely get loads of input current related noise though.

Graham

related

Seems to be unspecified. I know what you're thinking. I've used that configuration for test jigs - can't recall now if I did a sweep across the audio spectrum. JFET input btw.

Graham

I would be grateful for suggestions on constructing a simple random noise generator. Most of the noise should be within the audio spectrum.

R

Thanks. Radioshack stuff is unavailable for me. The second option is more in line with what I anticipated. Will one operational amplifier be sufficient? I am not interested in the quality of the noise but merely getting sufficient to drive a small speaker fairly hard.

Roger.

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noise

The cheapest FM radio would still need an amplifier as the speaker has to be well separated from the signal generator in the application that I have in mind.

R

I used a circuit I found that used a saturated transistor few parts and a 9 V. Very simple and I put it into the mike input of a portable radio. Worked great as a noise blanker for the babies room. Richard

You might want to check out my DaqGen freeware at

It uses the sound card on any Windows computer and can generate all sorts of test signals, including non-repeating white and pink noise as well as band-limited noise. You can see the real-time waveform or spectrum of the noise, average to see flatness over time. or run a histogram to get the amplitude distribution.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

Home of DaqGen, the FREEWARE signal generator

You can't really zener a 12-volt zener from a 12-volt supply.

And 741's are notoriously noisy themselves, which can cut both ways.

John

If you use a 6-ish volt zener, it can be the supply splitter, too!

John

See my sketch in a.b.s.e.

John