Noise generator circuit

Posted on Feb 7, 2014

This circuit delivers a plentitude of noise, a veritable harvest of noise, yes, I dare say. an abundance of noise. Noise, noise and more noise. This circuit gives you white noise, pink-ish noise, high pass noise, grainy noise (with grainy adjust), and lastly adjustable random gates. Noise lovers take heart this board was made for you.

Noise generator circuit
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In the Noise Cornucopia, the noise source is the reverse-biased emitter-base junction of Q1. We cut off the collector of Q1 so that it doesn`t act like an antenna picking up unwanted noise or EMI. The BVEBO (Emitter-Base Breakdown Voltage) is exceeeded thus the transistor is operating in avalanche mode. More noise info can be found here: Random Electrical Noise: A Literature Survey - by Terry Ritter. The positive supply voltage is applied to the emitter of Q1 via R33 and R2, 470K resistors in series. Capacitor C18 filters the voltage applied to the emitter to reduce the possibility of supply ripple getting into the noise output. Q1`s base is connected to the negative supply via R34, 10K resistor. This configuration results in more symmetry in the noise output. The noise generated at the EB junction of Q1 is capacitively coupled to the non-inverting input of U1-A which is biased to ground by R4 (2M) resistor. A gain of 48 is added by U1 and it`s output is fed capacitively to adjustable gain block U1-B. R5 is used to adjust the level of the noise at the output of U1-B to approximately +/-5V P-P. I found that just about any 2N3904 provided enough noise for this circuit but you may have to try a few to find the noisiest. Try to find the one that needs the least gain out of the second gain block to give you the required +/-5V P-P. The 2N5172 is another good noise transistor choice but note the difference in the pinout if you use...

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