White Noise Source

It needs a tinfoil beanie! :)

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Oh, It's fine as is. I just find it weird, somet'ing is triggering the zener. I 'smells' like a photon making electron hole pairs... shallow trap states? I need to know more about what's inside.

George H.

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Yeah but the specturm is still pretty flat. No signs of some frequency. (on a Tek 'scope FFT))* And it was the same 60 Watt incandesent that caused the "through tape" leakeage. Pretty much DC with some nice gentle 120 on the top.

I was also thinking about some pinhole in the tape... but I've got two diodes, a pin hole in one, would make the amplitude asymmetric... no signs of that.

The front panel was being 'made pretty' today. But tomorrow, I can measure some numbers. (I should post a pic. The Audio Amp has a gain of eleven!)

George H.

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Phil Hobbs

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Opps, "Mystery Managed". Operater error... I've got a two sets of diode on the pcb. I had the wrong set covered with tape. The Zeners were still 'wide open'.

Moving the tape to cover the 'noise diodes' fixes the light sensitivity problem... Duh!

George H.

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That's the sort of thing that never happens without a large and appreciative audience. Been there.

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Grin... I had this whole list of different experiments I wanted to try today.

Now I can do something productive.

George H.

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I hate when I do that... and it's not a rare occurrence.

Darn... I was thinking that it might be fun to investigate stuff in the IR range using your technique of masking the diodes with visually opaque tape that passed IR. A whole new area to check out...

Oh, well. Better luck next time.

BTW, after all this, I opted to just use software-generated noise for my brief experiment. I'll put together a hardware version that I'll likely use for testing circuits (amps and such).

Thanks again for all the great ideas. You guys sure taught me a lot about all this stuff - which I guess is the idea.

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rs

Yup, I had an exciting morning driving in to work thinking about different things I might try... Then reality punches you in the nose.

Well it might not be a complete waste. I 'someday' want to make a variable noise source that shows how shot noise depends on the size of the electron. Current noise density i sub n =3D sqrt(2*e*I), (amps/sqrt Hz). Where I is the average current. So if you could turn a knob and make electrons four times bigger, (while keeping the average current the same.) Then the noise density would go up by a factor of 2. In my model this is exactly what's going in in the zener. With no light I get big pulses but not very often. With the light on you get less noise. Because an absorbed photon makes an e-h pair and this can cause the zener to discharge sooner than it would have without the photon. The average current is kept roughly constant by the zener bias resistor.

Digital sources are nice, because (in theory) you should know exactly how much noise you are making.

George H.

Sounds interesting... never would have thought of it.

Personally, I don't feel most of my mistakes (in electronics) are a waste. If nothing else, I wind up learning something.

For example: I learned to make sure there's nothing between me and the door when I power up a circuit I've built. Also, try not to be the high- value resistor that discharges high voltage capacitors. There are endless opportunities for learning, if you don't incinerate yourself.

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I just wanted to cross the final Zed on the 20V Zener noise source run off the +/-15 V power rails.

I had other circuit 'stuff' leaking into the noise source. Turns out it has about zero PSRR. (As I should have guessed since this particular mistake has bitten me before.) I threw a cap multiplier at it, and that worked fine... though perhaps overkill. So for clean noise, well filtered power is important.

The light sensitivity of the zener was useful, I could turn on an incandescent and kill the noise by 40dB... that made it easy to see what was underneath.

George H.