Noisy noise generator

[Grant Richter]

The 1967 Motorola Zener Diode Handbook has a noise generator circuit.

To quote:

"A special zener noise diode is used in this circuit as the noise generating
element. This special zener appears to be superior to the transistor
junctions used in the past for these applications. These devices easily meet
a minimum wide band noise of 10 mV rms and some do even better. In order to
obtain maximum noise the zener is operated in the voltage current "knee"
region just proceeding the rapidly increasing zener current Iz."

The circuit shown is a normal zener shunt circuit with a current limiting
resistor of 1 megohm. Then is AC coupled to an amp with a 0.1 uF cap.

I believe the reverse biased transistor junctions use the E-B breakdown
voltage as a zener diode. Most E-B breakdown voltages are around 5 volts for
a 2N3904. Presumably any semiconductor junction in a "trickle" current mode
will maximize the noise output of the junction.

I put a socket in my Minimodular noise generator so I could try some
experiments. Initially I just used 10 different 2N3904 transistors. Noise
performance varied widely from 0.74 V rms (after amplification) to 1.35 V
rms. I'll try some zeners and other type of diodes and post the results.

----------
>From: Scott Gravenhorst <music.maker at gte.net>
>To: synth-diy at node12b53.a2000.nl
>Subject: Re: Noisy noise generator
>Date: Wed, Oct 18, 2000, 8:35 AM
>

> I'm curious about why zeners were chosen here.  Are they
> notably the most noisy silicon device?
>
> My personal experience with this was after trying several
> reverse biased BE junctions of small signal bipolar
> transistors, I (on a whim) tried a germanium diode and
> found it to have a sufficiently high noise level that I
> could use a fairly low gain amplifier and no shielding
> was required.
>
> YMMV.
>
> -- Scott Gravenhorst : On The Edge, but the Edge of What?
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>
>