White / LF Noise Generator

White / LF Noise Generator

Every musician today is in need of a noise source, particularly those who practice with a group or use a synthesizer. The white noise generator gives an output to be fed to an amplifier. The white noise generated by the 12V zener diode is amplified 200 times along with the noise of the noisy 741 IC (IC1). The output is thus very noisy with plenty of white noise.
The output of IC1 is given to a low pass filter which cuts off high frequencies. Point A is connected to amplifier IC2. The feedback network of IC2 includes a 0.15 µF capacitor which reduces the gain at high frequencies.
The 0.001 µF capacitor at the output of IC2 also loads the output at high frequencies and reduce them. Thus the resultant output has a large amount of low frequency (LF) noise.
A small amount of white noise due to the IC itself is produced at the output, but it can be ignored. Point B is an artificial center point created for IC1 and IC2. Point C is connected to the capacitor which reduce the gain of IC2 at high frequencies.

Circuit diagram of White-lf noise

Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise)
R1 = 470 KΩ
R2, R5, R8, R9 = 10 KΩ
R3, R6, R10 = 100 KΩ
R4 = 4.7 KΩ
R7 = 1 MΩ
C1 = 0.47 µF
C2 = 100 µF/10v
C3, C6 = 1 µF/16v
C4 = 0.15 µF
C5 = 0.015 µF
C7 = 0.001 µF
C8 = 100 µF/25V
IC1, IC2 = 741

ZD1 = 12V 400mW