Portable white noise generator

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

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.

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!

richardc64

PHOBoS · Posted: Fri Feb 01, 2013 3:03 pm Post subject:

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

-minus- · Joined: Oct 26, 2008 Posts: 787 Audio files: 13

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.

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

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!

Mikmo

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?

fluxmonkey · Joined: Jun 24, 2005 Posts: 707 Location: cleve

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.

richardc64

elektrouwe · Joined: May 27, 2012 Posts: 109 Location: Germany

bubzy · Posted: Sun Jan 05, 2014 2:19 am Post subject:

or. you can code a PIC up like this

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