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Old 28th March 2012, 04:48 PM   #11
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A 604K resistor and just about any FET op-amp (or a JFET follower for that matter) makes a nice 100nV/root-Hz white noise.
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Old 28th March 2012, 10:27 PM   #12
Simon B is offline Simon B  United Kingdom
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Quote:
Originally Posted by scott wurcer View Post
A 604K resistor and just about any FET op-amp (or a JFET follower for that matter) makes a nice 100nV/root-Hz white noise.


Temperature compensation is left as an exercise to the reader....!
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Old 28th March 2012, 11:41 PM   #13
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At one time I was looking for highest noise volts out for minimum microamps in and I wound up with 1M into a revered biased 3904 base emitter junction feeding a mu follower. Drawback is you need at least 10V supply to make it practical. More than a 9V battery except brand spanking new, anyway.

Last edited by Andrew Eckhardt; 28th March 2012 at 11:43 PM.
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Old 29th March 2012, 02:59 AM   #14
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Originally Posted by Simon B View Post


Temperature compensation is left as an exercise to the reader....!
Pretty weak variation around room temperature, though in the UK it is probably noticably lower.
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Old 29th March 2012, 07:18 AM   #15
benb is offline benb  United States
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Originally Posted by LAJ View Post
I built one of those before but using an op amp for the amplifier. I didn't think it worked very well.
But from the National Semiconductor 1980 Audio/Radio manual page 2-62 it states:
Unlike semiconductor noise sources, the MM5837 provides very uniform noise quality and output amplitude.
The MM5837 uses a clocked shift register to generate noise which I thought was a much better approach.
The chip's output is "uniform" because it repeats every couple of seconds. If you measure its peak output for a few seconds, you've measured the highest peak output it will ever give. It's like a two-second tape loop of recorded noise that gets played back over and over (once you hear it loop through a few times it actually SOUNDS like a two-second tape loop of recorded noise). This can be useful when you want to make the noise drive something to just below clipping, and need to know that it will never clip. With an analog noise source it may eventually clip, as the level is "truly" random and you don't know what the peak may be.

Here's a description of a PIC microcontroller replacement:
White Noise Source based on PIC 12F processor
The PIC code described is "better" in that it has a much longer period, but once gain that's not always what you want.
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Old 31st March 2012, 12:25 PM   #16
tvrgeek is offline tvrgeek  United States
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I just use my PC. White, pink, whatever. Want it portable? Make a CD.
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