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Portable white noise generator
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amicoleo



Joined: Jan 31, 2013
Posts: 4
Location: Italia

PostPosted: Fri Feb 01, 2013 8:56 am    Post subject: Portable white noise generator Reply with quote  Mark this post and the followings unread

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.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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
Posted Image, might have been reduced in size. Click Image to view fullscreen.
(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
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PostPosted: Fri Feb 01, 2013 11:50 am    Post subject: Re: Portable white noise generator Reply with quote  Mark this post and the followings unread

cagnarrogna wrote:
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...

Yeah, that's wrong. R6 and R7 should form a voltage divider, providing the (+) input with 1/2 Vcc. Try moving the end of R7 shown connected to Ground to the opamp + pin instead.

If that doesn't improve things, try wiring the noise source the same as the second circuit, which most definitely does work at 9V. If THAT doesn't sound better, try my circuit.


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PHOBoS



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PostPosted: Fri Feb 01, 2013 3:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

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. Rolling Eyes

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-minus-



Joined: Oct 26, 2008
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PostPosted: Fri Feb 01, 2013 4:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

PostPosted: Sun Feb 03, 2013 3:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey!

yeah, my 9v battery wasn't really providing 9v... Embarassed

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

PostPosted: Sun Dec 29, 2013 2:31 pm    Post subject: Problem with white noise generator Reply with quote  Mark this post and the followings unread

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?

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fluxmonkey



Joined: Jun 24, 2005
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PostPosted: Tue Dec 31, 2013 12:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.
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richardc64



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PostPosted: Tue Dec 31, 2013 3:21 pm    Post subject: Re: Problem with white noise generator Reply with quote  Mark this post and the followings unread

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.

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elektrouwe



Joined: May 27, 2012
Posts: 36
Location: Germany

PostPosted: Sat Jan 04, 2014 3:53 pm    Post subject: Re: Portable white noise generator Reply with quote  Mark this post and the followings unread

amicoleo wrote:

Any suggestion?

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
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PostPosted: Sun Jan 05, 2014 2:19 am    Post subject: Reply with quote  Mark this post and the followings unread

or. you can code a PIC up like this

http://www.electricdruid.net/forums.html?page=projects.noisegen

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