Noise source

nicolas3141 · Posted: Tue Jun 02, 2009 2:38 am Post subject: Noise source

This is an audio spectrum noise source, with no filter to shape it to any 'colour'. I leave that as an exercise for the reader if they wish ;~)

Depending on your zener diode the output level may be a bit different from mine. If you find the output level too hot (especially if it is sometimes clipping), reduce R5 proportionally (try 50-100K). If you want to boost the output level, replace R2 with a capacitor (say 200-300n) and a smaller resistor (try 3-6K) in series (0V to cap, cap to R2, R2 to R5 and U1 as before).

The exact voltage of the zener is not critical, anything 10-13V would do. But lower voltages produce less noise so are not so good. Any op-amp can be used. Any npn transistor with good gain is fine - no need for low noise!

The R1/C3 and R4/C5 arrangement is to prevent power supply crap getting through to the output, but if your power supply is very clean you may not need them. If your power supply is particularly unclean you may need to increase the size of C3 and C5 (and C1 and C2). C3 and C5 give the circuit an interesting slow-start characteristic which reminds me of my youth and listening to an old valve radio starting up.

Cheers,
Nicolas

noise-741.JPG

Description:

Filesize:

40.41 KB

Viewed:

18853 Time(s)

nicolas3141 · Posted: Tue Jun 02, 2009 2:41 am Post subject:

Cripes that post makes me sound old. But then I feel old since turning forty the other day Sad

nicolas3141 · Posted: Tue Jun 02, 2009 2:45 am Post subject:

Oh and yes it should run fine on +/-12 or +/-15V. On higher voltage supplies you could try a higher voltage zener, say 15V. You would probably also want to boost the output a bit by replacing R2 with a cap and smaller resistor as described above.

Cheers,
Nicolas

Pehr · Posted: Tue Jun 02, 2009 4:15 am Post subject:

Brilliant! Very Happy

oculus · Joined: Oct 30, 2011 Posts: 35 Location: Iceland, Reykjavik

hi Nicolas. thanks once again for a great project.

i just tried breadboard this it seems to work but it did sound a little weird to me at first to much low end and a little weak but then i moved my hand and blocked the light going on the breadboard and it sounded a little better

so i tried turning of the lights and then it sounded about right.
it seems to me that the light is affecting the diode. is this normal?
i just ordered the diode you listed so i should have the same as you listed.

here is a sample of this behavior
(you might have to do right click and save link as)
http://dl.dropbox.com/u/4440248/drasl/Noise%20light%20problem.mp3

later i tried changing battery´s and it sounded little more constant but still. here is a sample of that
http://dl.dropbox.com/u/4440248/drasl/Noise%20light%20problem.mp3

thanks kind regards
Fridfinnur

oculus · Joined: Oct 30, 2011 Posts: 35 Location: Iceland, Reykjavik

i forgot to mention i don´t know if this matters but i have R2 2.2k for more output and R5 220k as i didn´t have 200k

thanks Fridfinnur

frijitz · Posted: Tue Nov 15, 2011 6:23 pm Post subject:

Have you measured the spectrum of the output noise?

Very Happy

Ian

frijitz · Posted: Tue Nov 15, 2011 7:35 pm Post subject:

OK, I just had a real quick look at the posted files. In the dark, the spectrum is nice and flat over the mid-audio range with -6dB rolloffs at 30Hz and 16kHz.

The high-frequency rolloff seems due to the limited GBW of the 741 opamp. GBW = 1*10^6, Gain = 100 ==> BW = 10kHz. A faster opamp should give you a bit more "air" at the top end.

In the light, any diode will operate as a photodetector. The spectrum has strong peaks at 100, 200 and 300Hz ... obviously line frequency pickup via the room lights. The 100Hz component is very strong, in agreement with what you hear.

Anyway, it's a nice little circuit. Simple and effective.

Very Happy

Ian

oculus · Joined: Oct 30, 2011 Posts: 35 Location: Iceland, Reykjavik

Nice thank you. I didn´t know about the light affecting diodes.
i just finished the noise on vero board. I changed a few things

i used tl72, i changed the c6 into 1uf ceramic, R2 - 2.2k, r5 - 220k,
and i switched the Bc549 into Bc547 it sounded to me a littlebit less agressive in the hi mid but it had something around 2 db less output.

kind regards Fridfinnur

elanhickler · Posted: Sun Jul 08, 2012 7:00 am Post subject:

is this the tube radio thing the OP was describing?: http://www.youtube.com/watch?v=06kKjW0u9Fs&feature=related

elanhickler · Posted: Tue Oct 30, 2012 5:25 pm Post subject:

How does one translate this circuit to a 15v PSU?

bubzy · Posted: Wed Oct 31, 2012 12:18 am Post subject: Re: Noise source

elanhickler · Posted: Wed Oct 31, 2012 6:51 am Post subject:

already anwered. not sure how I missed that, I've read this thread like 5 times.