[sdiy] Vote for your favorite noise source

[Scott Bernardi]

I've used both the pseudo random shift register type and reversed biased
pn junctions.  The reverse biased pn junction is a much lower parts
count, but you have to be very careful with layout and supply leads
because it is a high gain circuit and it will amplify thumps in your
supply lines (like from LFOs).  Also, there is some experimentation you
have to do with the noise transistor and the amount of gain you need.
Use multiple cascaded gain stages rather than one stage with large gain
to preserve HF bandwidth (opamps rolloff high frequencies quite rapidly
at high gains).
The nice thing about pseudo random is that the level of the output is
consistent, you can run it off your "dirty" five volt supply, and you
don't have to worry about thumps in your supply. If you have enough
stages there will be no detectable pattern (18 stage shift register
repeats once every 8 minutes or so).

Sound wise, they are about the same.  If I were going for "ultimate"
noise source I'd probably use a pseudo random with white, pink, and low
frequency random outputs.  Here's a circuit I used in my original OGEE
synth. If I was doing it again I'd redesign it using CMOS, and use just
a zener for the DAC reference (REF-01 is overkill, but I worked at PMI
at the time so I had access).
http://home.attbi.com/~sbernardi/elec/noise.html

Tim Ressel wrote:

> Okay boys and girls, Its time to throw caution to the
> wind and start a new holy war:
>
> Part 1:
>
> (*)-(*)-(*)-(*)-(*)-(*)-(*)-(*)
> Which Noise Source Is The Best?
> (*)-(*)-(*)-(*)-(*)-(*)-(*)-(*)
>
> Candidates:
>
> Reversed-biased PN junstion (2N2712)
> Above with constant-current source
> Reversed-biased zener
> Dual reversed-biased zener (MOTM??)
> Mondo shift register with feedback
> Small hungry infant
> Other?
>
> Part 2:
>
> (*)-(*)-(*)-(*)-(*)-(*)-(*)-(*)
> Which Pink Filter Is The Best ?
> (*)-(*)-(*)-(*)-(*)-(*)-(*)-(*)
>
> Have fun!
>
> --TR
>
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--
Scott Bernardi
sbernardi at attbi.com