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Old 20th March 2012, 06:25 PM   #1
LAJ is offline LAJ  United States
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Default White Noise Generator

Has anybody used any of the Homedics sound machines for a white noise generator? That have white noise and several other noises on them.
I see them at the thrift shops for $1-$2 each which is probably less than you can build one for. Thanks.
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Old 22nd March 2012, 03:44 PM   #2
LAJ is offline LAJ  United States
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Default I bought it for $1.68.

It makes other sounds as well like a brooke running, birds chirping, rain falling.
I'm thinking that this will not disturb my neighbors as much when I am testing a high power amplifier on my back patio as a tone oscillator does.
And they won't call the cops on me.
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Old 23rd March 2012, 06:57 PM   #3
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But I doubt that it's a technically correct "white noise" suitable for measurements.
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Old 26th March 2012, 04:20 PM   #4
LAJ is offline LAJ  United States
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Default Thanks Kev...

but have you seen what the MM5837 chips are going for on Ebay????
YIKES!!!!!! There's one for $10 and another for $23!!!!!!
Unbelievable!!!!!
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Old 26th March 2012, 06:33 PM   #5
RJM1 is offline RJM1  United States
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White Noise.
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File Type: jpg white noise.JPG (11.3 KB, 132 views)
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Old 28th March 2012, 03:21 PM   #6
LAJ is offline LAJ  United States
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Default Thanks RJM...

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.
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Old 28th March 2012, 03:33 PM   #7
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Long time ago I used a electrolytic cap reversed, and wired with a high resistance in series, limiting current so some microamperes, and acting as load, and using a 1 uF 50V powered from 12V, and it works very fine.
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Old 28th March 2012, 03:34 PM   #8
Frex is offline Frex  France
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Hi Laj,

Did you have the spectrum profile of the noise generated by the MM5837 ?
I think for audio (and more) use, the application note DN70 from Linear Technology
is a very good solution.
Regards.

Frex
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Old 28th March 2012, 04:14 PM   #9
PChi is offline PChi  United Kingdom
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Hi,
I reverse engineered the internal circuit of I think the MM5837 and then built a version from shift registers (from memory I think that it's 17 stages) and Exclusive OR gates for generating a psuedo random digital signal. Used for testing Motorway 'Information' sign communication signals. The signal appeared pretty random on the valve oscilloscope that I used. I guess that up to the clock frequency it is a good white noise source.
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Old 28th March 2012, 04:16 PM   #10
BFNY is offline BFNY  United States
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an analog FM tuner tuned to a blank point on the dial with no station works too.
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