White noise generator

[Roger Dewhurst]

I would be grateful for suggestions on constructing a simple random noise
generator. Most of the noise should be within the audio spectrum.

R

 

[John Larkin]

I would be grateful for suggestions on constructing a simple random noise
generator. Most of the noise should be within the audio spectrum.

R

Radio Shack sells a little amplified-speaker box, $9 or something.
It's very noisy, and should output a reasonable amount of noise via
the headphone jack. I can't vouch for its statistics.

The more formal way to do this would be to bias a low-power 10-volt
zener to maybe 1 mA current, and amplify that. Figure the zener will
make roughly 300 nV/rootHz noise density, or about 40 microvolts RMS
in the audio KHz range.

You can also make noise digitally, with a pseudo-random shift
register. See AoE.


John

 

[Roger Dewhurst]

Radio Shack sells a little amplified-speaker box, $9 or something.
It's very noisy, and should output a reasonable amount of noise via
the headphone jack. I can't vouch for its statistics.

The more formal way to do this would be to bias a low-power 10-volt
zener to maybe 1 mA current, and amplify that. Figure the zener will
make roughly 300 nV/rootHz noise density, or about 40 microvolts RMS
in the audio KHz range.

You can also make noise digitally, with a pseudo-random shift
register. See AoE.


John

Thanks. Radioshack stuff is unavailable for me. The second option is more
in line with what I anticipated. Will one operational amplifier be
sufficient? I am not interested in the quality of the noise but merely
getting sufficient to drive a small speaker fairly hard.

Roger.

 

[Ralph Mowery]

I would be grateful for suggestions on constructing a simple random noise
generator. Most of the noise should be within the audio spectrum.

Tune a cheap FM radio inbetween stations.

 

[Roger Dewhurst]

Tune a cheap FM radio in between stations.

The cheapest FM radio would still need an amplifier as the speaker has to be
well separated from the signal generator in the application that I have in
mind.

R

 

[Pooh Bear]

I would be grateful for suggestions on constructing a simple random noise
generator. Most of the noise should be within the audio spectrum.

I use a 10 Megohm resistor and amplify the f**k out of it with a low noise
op-amp.

Graham

 

[Pooh Bear]

Radio Shack sells a little amplified-speaker box, $9 or something.
It's very noisy, and should output a reasonable amount of noise via
the headphone jack. I can't vouch for its statistics.

The more formal way to do this would be to bias a low-power 10-volt
zener to maybe 1 mA current, and amplify that. Figure the zener will
make roughly 300 nV/rootHz noise density, or about 40 microvolts RMS
in the audio KHz range.

Don't semiconductor junctions make excess shot noise though ?

You can also make noise digitally, with a pseudo-random shift
register. See AoE.

Nat Semi once made a chip that did that. I have a 'little box' I made using
one. Sounds horrid. You can hear the pattern.

Graham

p.s. I've sometimes heard shot noise referred to a Schott noise. Any idea
which is correct ?

 

[BobG]

Any reverse biased eb junction is noisy like a zener diode. This is
white noise... equal energy per hz... you want pink noise? (equal
energy per octave)

 

[John Larkin]

Don't semiconductor junctions make excess shot noise though ?

At this sort of current, zeners are pretty white and gaussian, maybe
just a tad asymmetric. At much lower currents, shot noise is
significant.

Nat Semi once made a chip that did that. I have a 'little box' I made using
one. Sounds horrid. You can hear the pattern.

The sequence must have been short. A 1 MHz, 64-bit shift register
won't repeat in your lifetime.

Graham

p.s. I've sometimes heard shot noise referred to a Schott noise. Any idea
which is correct ?

I think it's "shot", like buckshot falling on the roof.

John

 

[John Larkin]

Thanks. Radioshack stuff is unavailable for me. The second option is more
in line with what I anticipated. Will one operational amplifier be
sufficient? I am not interested in the quality of the noise but merely
getting sufficient to drive a small speaker fairly hard.

Roger.

I's suggest two opamps, each with a closed-loop gain of, say 50, to
get you up to 100 millivolts RMS, then some sort of power amp to drive
the speaker, one of those cheap National thingies maybe. A single
opamp might work, ahead of the amp, depending on your numbers... x1000
at 3KHz requires at lease a 3 MHz gain-bandwidth opamp.

John

 

[John Larkin]

I use a 10 Megohm resistor and amplify the f**k out of it with a low noise
op-amp.

Graham

The opamp noise would probably wind up dominating the resistor noise.
That might be OK, but opamp noise tends to be fairly non-white, with a
lot of excess low-frequency (1/f) component and occasional pops and
other weirdness.

John

 

[Pooh Bear]

The opamp noise would probably wind up dominating the resistor noise.
That might be OK, but opamp noise tends to be fairly non-white, with a
lot of excess low-frequency (1/f) component and occasional pops and
other weirdness.

John

I make 10 Meg = 409 nV / sqrt Hz

Used with a TL07x type op-amp ( 12 nV / sqrt Hz ) it seems to be just fine.

With a bipolar op-amp you would indeed likely get loads of input current related
noise though.


Graham

 

[John Larkin]

I make 10 Meg = 409 nV / sqrt Hz

Used with a TL07x type op-amp ( 12 nV / sqrt Hz ) it seems to be just fine.

With a bipolar op-amp you would indeed likely get loads of input current related
noise though.


Graham

Yeah, that works. What's the input capacitance on one of those?

John

 

[Pooh Bear]

Yeah, that works. What's the input capacitance on one of those?

John

Seems to be unspecified. I know what you're thinking. I've used that configuration
for test jigs - can't recall now if I did a sweep across the audio spectrum. JFET
input btw.

Graham

 

[Brian]

I would be grateful for suggestions on constructing a simple random noise
generator. Most of the noise should be within the audio spectrum.

R

Check out http://www.discovercircuits.com/N/noisegen.htm Also go to Google
and put it "white noise circuits", there is a lot of good information there.

Brian

 

[Bob Masta]

I would be grateful for suggestions on constructing a simple random noise
generator. Most of the noise should be within the audio spectrum.

You might want to check out my DaqGen freeware
at www.daqarta.com. It uses the sound card on any
Windows computer and can generate all sorts of
test signals, including non-repeating white and pink
noise as well as band-limited noise. You can see the
real-time waveform or spectrum of the noise, average to see
flatness over time. or run a histogram to get the
amplitude distribution.

Best regards,


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

 

[spudnuty]

Check out http://www.discovercircuits.com/N/noisegen.htm Also go to Google
and put it "white noise circuits", there is a lot of good information there.

Brian

I used a circuit I found that used a saturated transistor few parts and
a 9 V. Very simple and I put it into the mike input of a portable
radio. Worked great as a noise blanker for the babies room.
Richard

 

[Roger Dewhurst]

I's suggest two opamps, each with a closed-loop gain of, say 50, to
get you up to 100 millivolts RMS, then some sort of power amp to drive
the speaker, one of those cheap National thingies maybe. A single
opamp might work, ahead of the amp, depending on your numbers... x1000
at 3KHz requires at lease a 3 MHz gain-bandwidth opamp.

John

Thanks. Would a 741op-amp drive a small speaker? If so would two or three
of these in series do the job? Would you bias the + input to half the
single supply voltage (12 volts) in each case and use 470pf capacitors
between the zener diode and the first stage, between each stage and between
the last stage and the speaker?

Roger

 

[Never Mind]

The cheapest FM radio would still need an amplifier as the speaker has to
be well separated from the signal generator in the application that I have
in mind.

It would help if you described your application. (The PP was referring to
using an FM radio with NO signal)

Since you mention a speaker, do you really need white noise, or just some
"noise"?

 

[Roger Dewhurst]

It would help if you described your application. (The PP was referring to
using an FM radio with NO signal)

Since you mention a speaker, do you really need white noise, or just some
"noise"?

Noise across the audio spectrum of a small speaker. The speaker will be
some metres away from the signal generating part of the device. The noise
level must be controllable nearly upto the limit of the speaker.

I have just about come around to the idea of a 12 volt Zener diode driving
two LM741s followed by a LM368N to drive the speaker. The op-amps would
have a 12 volt unbalanced supply with the + inputs of the LM741s biassed to
6 volts. The parts are all available and cheap. I have the speaker. Would
this work in your view?

R