Portable white noise generator

[cagnarrogna]

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!

[richardc64]

[PHOBoS]

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.

[-minus-]

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.

[cagnarrogna]

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!