Noisy BJT + Gain stage = white noise?

[Brisance]

So I figured I need a whitish noise or similiar generator to best evaluate my tone circuits and I figured, why not just get a particularly hissy/damaged bjt, maybe hook up some 10M resistors as well for extra noise and just run it through a gain stage? Has anyone done this?

[merlinb]

People have been making noise generators ouf of reverse-biased transistors for donkey's years. A zener works too:
http://www.edn.com/design/analog/4420926/White-noise-source-flat-from-1Hz-to-100kHz

[antonis]

I think that is a very rough aproximation..

You'll get better results with a zener diode and an Op amp...


edit: merlinb is faster than me...

[smallbearelec]

a whitish noise or similiar generator to best evaluate my tone circuits

http://smallbear-electronics.mybigcommerce.com/2n2712-work-alike-noisemakers/

[Brisance]

Thanks, love your site and have contemplated ordering some stuff, but ordering noisy BJTs from basically the other side of the world seems a little... overkill. Especially considering I have hoarded bunch of soviet germaniums and such in many configurations among other stuff. I also figured I'd build the generator without going to the store as per my recent habit(all the hoard needs utlizing after all) unless something very exotic is needed.

Great to learn, that there are "dedicated" noisy transistors for the task though! Will probably order some other stuff from you one day tho

[PRR]

{EDIT} There's LOTS of stuff on this forum about hiss generators.

Two stages of TL072 cascaded as a high gain amp, input grounded, with a little bass-cut, seems to make a fairly predictable smooth White Noise source.

You do not want to listen to White Noise for long! You want a Pink filter. If you are not doing precision measurements, EV's old speaker-abuse noise filter is a fair compromise and even cheaper than a Pink.

[PRR]

> Two stages of TL072

http://www.diystompboxes.com/smfforum/index.php?topic=105885.msg955626#msg955626

[Brisance]

Thanks PRR! I might just make one like that, but use 741s instead, since I have a heap of them and mostly use TL072s and 01s for other projects