[sdiy] Help with (lack of) noise circuit

[Oren Leavitt]

On 12/21/2013 5:52 PM, Tim Ressel wrote:
> Funny how the simplest circuits can kick your butt. I'm trying to do the classic transistor noise generator, with no luck. I started with a 2N3904 with the emitter to +12 with a 100K resistor and the base to ground. I've tried resistors from 500 ohms to 1 meg, voltages up to 24 volts, and different transistors (PN2222, PN2484). No joy. What am I doing wrong?
>
> Thanks!
>
>

Tim, Having build a number of these myself, I've found about 470k to 1M 
is a good range for reverse bias current thru the transistor on a 12 to 
15 volt supply.
Be sure to AC couple the noise transistor via a capacitor to the input a 
high AC gain (say 500 to 1000x) amplifier. Use an AC gain configuration 
so that you don't amplify DC offsets.

If you can find one, try a 2N2712.

- Oren