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amicoleo

Joined: Jan 31, 2013 Posts: 4 Location: Italia
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Posted: Fri Feb 01, 2013 8:56 am Post subject:
Portable white noise generator |
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Hi everybody!
I want to build a simple white noise generator and I need it to be portable, so my idea was to have it powered from a 9v battery. I found this design from an old experimentalists anomymous forum post.
Here supply is 9v instead of usual 15v I've always seen from a 2 transistor noise circuit and I supposed the ampification stage after the 2 transistors is for compensating the weak signal is coming out from them. So I built the simplest 2 transistor noise circuit
(which despite from the 9v in the figure, with 2n3904 transistor works just with 12+ volts as supply) put an inverting opamp with about 45db gain at the output, and used a supply of 9v, but I had no success (nothing is coming out exept hum sound)...
There's one part of the first circuit I didn't really understand, which could be the cause of my problem: the + pin of the opamp is just connected to ground through a resistor? I don't understand why there's also the supply indicated there...
Any suggestion?
thanks! |
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richardc64
Joined: Jun 01, 2006 Posts: 666 Location: NYC
Audio files: 26
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PHOBoS

Joined: Jan 14, 2010 Posts: 3818 Location: Moon Base
Audio files: 565
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Posted: Fri Feb 01, 2013 3:03 pm Post subject:
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hmm I didn't have any succes with that simple white noise generator either. that is at 9V. It worked but I think I also needed to
provide at least 12V. I tried several similar ciruits, different kinds of transistors but all had the same problem. So in the end I just
made a voltage multiplier using a 555 to power it and that worked fine.  _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp AcidTrasH Stickney Synthyards |
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-minus-
Joined: Oct 26, 2008 Posts: 787
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Posted: Fri Feb 01, 2013 4:25 pm Post subject:
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The simple two transistor design will work on 9V. I have used this several times. But it does need to be 9V. At 8V it will really be struggling to make noise. If you are using a battery, make sure it's new. Socket your transistors and test many of them to find the noisiest. I have had good results with PN100's or 2N2222's. |
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amicoleo

Joined: Jan 31, 2013 Posts: 4 Location: Italia
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Posted: Sun Feb 03, 2013 3:34 pm Post subject:
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Hey!
yeah, my 9v battery wasn't really providing 9v...
Many thanks richardc64 for the circuit, that was exactly what I was trying to achieve. I just didn't know (yet) how to make an inverting amp with a single supply! |
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Mikmo
Joined: Dec 01, 2005 Posts: 150 Location: Copenhagen - Denmark
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Posted: Sun Dec 29, 2013 2:31 pm Post subject:
Problem with white noise generator |
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I build the circuit that Richardc64 presented above. When i power it with a fresh 9V battery it work perfectly, giving good white noise. But if i power it with any powersupply i get hum, wails and abolutely no white noise.
I tried 3 different powersupplys, all of them work perfectly well with my oscillators, filters and all other modules (all simple Lunetta style yuff, running at 9V). It's only with the noise generator i have problems.
What can the problem be? _________________ Stay Cool
Mikael
http://www.mikmo.dk |
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fluxmonkey
Joined: Jun 24, 2005 Posts: 707 Location: cleve
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Posted: Tue Dec 31, 2013 12:25 pm Post subject:
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these circuits work by taking very small signals (from the reverse-biased transistor) and amplifying them tremendously. any hum or ripple at all in the power supply, or picked up from a breadboard or a stray wire, will easily swamp the noise signal itself. _________________ www.fluxmonkey.com |
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richardc64
Joined: Jun 01, 2006 Posts: 666 Location: NYC
Audio files: 26
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Posted: Tue Dec 31, 2013 3:21 pm Post subject:
Re: Problem with white noise generator |
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Mikmo wrote: | What can the problem be? |
I can't imagine. I powered it from a 9V regulator that delivered slightly less than 9volts.
Try listening to the transistors without the opamp. Is the 9v supply you're using single-supply, or "split" to provide +/-4.5V so that -9V isn't Gnd? Is the noise circuit's Vref being shared with other single-supply opamps? You can't do that.
The synth on your site is looking good, btw. _________________ "I’m a New Yorker, and I know a con when I see one.” -- Michael Bloomberg |
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elektrouwe
Joined: May 27, 2012 Posts: 109 Location: Germany
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Posted: Sat Jan 04, 2014 3:53 pm Post subject:
Re: Portable white noise generator |
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amicoleo wrote: |
Any suggestion?
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yes, forget to feed it directly from a 9V battery. As others already said,
it CAN work if the battery is full and you have (hand selected) the right
transistors. Attached you find 2 noise generator schematics. Both use
a simple boost converter to get the required > 15V for good noise output.
The 1st uses a common mode choke in a selfoscillating converter.
You can get these from any dead switchmode power supply ( eg. PC) so no need to buy one. It runs from 2 AA or AAA cells (2...3V). The 2nd uses a simple
330uH choke (value & size not critical, but you have to tune to resonance
if you use other values than the shown ones) , driven by a simple square
wave osc. that is fed from a 9V battery.
I've build both noisegens.many times and never had to select transistors.
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bubzy

Joined: Oct 27, 2010 Posts: 590 Location: United Kingdom
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