UBZR1 Noise Generator Module

Chelys Lyra

Summary/Usage

The Noise module serves two purposes:

a white or pink noise audio source to synthesize non-periodic sounds
a pink or "red" noise source to use for random type modulation

Functional Description

The noise module uses a transistor operated in reverse mode above breakdown voltage with current limited.

The following opamp circuits filter for

white noise
pink noise with a flat power spectrum per octave: d p / d ln f = constant
"red" noise with still more emphasis on low frequencies than pink noise.

Final amplification is done with an LM 13700 transconductance amplifier, which serves as a built-in VCA and provides for two separate current outputs, one for white/pink noise and one for pink/red noise. The former can be used in the audio path, the latter is available in the modulation matrix.

Performance Specs

‑ to be documented ‑

Schematics as SVG Files

Noise Block Schematics

Noise Generator Schematics

Noise Selection and VCAs Schematics

Noise Exp. Current Sources Schematics

Interface

Inputs

Continous control voltage (−5 V to +5 V) input to control volume (output #0)
Continous control voltage (−5 V to +5 V) to further adjust output amplitude of Pink/Red output (output #1). To be connected to a "wheel" control
Logic level input (0 V or +5 V) to switch off output #0 (at logic level +5 V)
Logic level input (0 V or +5 V) to select between white or pink noise for output #0
Logic level input (0 V or +5 V) to select between pink or red noise for output #1

In UBZR1, that latter two inputs are wired together outside of the Noise module board, because outputs #0 and #1 are not likely to be used at the same time.

Outputs

White/Pink current output (−0.5 mA to +0.5 mA maximum)
Pink/Red current output (−0.5 mA to +0.5 mA maximum)