Re: White noise generator

On Tue, 27 Dec 2005 10:00:34 +1300, "Roger Dewhurst"
<dewhurst@xxxxxxxxxx> wrote:

>
>"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
>news:t6k0r1lbkip5hbs72jtdllmv00kad3ifc6@xxxxxxxxxx
>> On Tue, 27 Dec 2005 09:03:21 +1300, "Roger Dewhurst"
>> <dewhurst@xxxxxxxxxx> wrote:
>>
>> >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
>
>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

.

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