Noisy noise generator

[Hairy Harry]

Hi Michael... How about trying an additional Zener
shunt regulator before your noise zeners... like pre-regulate
to +/- 10V, then try the zener noise source...

BTW why the two zeners... why not just one ??? you could
buffer the noise with a voltage follower op-amp, then use that
to drive a AC coupling cap into a big gain stage...

Also a steel box around the circuit might help. I've had lots
of trouble with external magnetic fields lately (hi gain fuzzbox)

H^) harry


>From: Michael Buchstaller <buchi at takeonetech.de>
>Reply-To: buchi at takeonetech.de
>To: synth-diy at node12b53.a2000.nl
>Subject: Noisy noise generator
>Date: Sun, 15 Oct 2000 00:10:34 +0200
>
>Hello list members,
>
>again i am buggering you with one of my silly questions.
>
>I wanted to make a very simple noise source for my modular. So i took two 
>zeners
>in series; a resistor to V+ and one to V-;  the junction between them 
>should go via a
>small decoupling cap into an opamp.
>
>OK, it sorta works, but the output is very weak and rides on approx. 100 mv 
>of a distorted
>50 Hz sine wave.  Now my first thought was that this would be mains cycles 
>bleeding through
>the power supply (a simple 7815/7915 combo on my bench), so i tried to 
>smooth it with lots
>of caps, but it did not change anything. When i probe the +, - and GND 
>lines with the scope
>probe, i cannot see any noise, hum or the like. I even shielded the zeners 
>with a grounded
>ring, but also no help.
>
>The (unwanted 50 HZ) noise is approx. 20 times the usable real noise 
>signal.
>
>I have used a LM324 in the 1st instance, then replaced it by a TL084, but 
>no change. (i did have
>only quad opamps here now, but i bet a 741 would not help, too)
>
>Here is the schemo and two photos of the experimental board:
>
>http://www.geocities.com/m100de/noise.html
>
>What am i doing wrong ???
>
>
>-Michael Buchstaller

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