Quad Noise white and colored sound source. Random voltage source.haraldswerk.de

Motivation

It is quite useful to have different adjustable noise and random voltage sources. Depending on your patch stile of course. Here is the quad version of my noise module from the NGF project. It is a combination of two original Elektor Formant modules. The noise module from Elektor Formant book one and the colored noise (CNC) module from book two. It provides four independent white noise outputs, four adjustable colored noise outputs with "red" "blue" adjustment. The four random voltage outputs are adjustable in speed of change. The noise is derived from the reverse biased BE diode of an NPN transistor.

Specs and features

Four independent white noise outputs
Four independent adjustable colored noise outputs with "red" "blue" adjustment
Four random voltage outputs, adjustable in speed of change
Four LED indicating the random voltage change
Runs on +/-12V and +/-15V
Power consumption around 65mA each rail

Implementation

Schematic

Description:

(Given for one of the four.) Noise source is the reverse biased BE diode of NPN transistor Q1 (B_090). The following operational amplifier IC1A and IC1B (B_090) amplifies the noise to 10Vpp. IC1C (B_090) is the buffer for the white noise output. IC2B (F_101) is configured as a 12dB low pass. So you get a low frequency random voltage. The changing speed is set with P3A/P3B (F_101) which sets the corner frequency of the low pass filter. IC2A / LED1 (F_101) makes the fluctuation visible. TR_1 (F_101) adjust the brightness of LED1 (F_101). In the feedback loop of IC1B (F_101) is an adjustable filter combination which gives you a wide range of adjustable colored noise with P1 and P2 (F_101). The output is buffered with IC1A (F_101).

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Calibration

Adjust the LED brightness to your needs with TR_1 .. TR_4

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Building hints

Select the noise transistor for loudest noise
If the noise is not loud enough increase the amplification off IC1B (IC2B, IC3B, IC4B) (B_090). Increase R7 (R8, R39, R40)