Chelys Lyra

UBZR1 Audio Path

UBZR1 Audio Path

The audio path is fully analogue. There are three voltage controlled oscillators (VCO) and a noise source. All four have built in voltage controlled amplifiers (VCA). Each of them has the option, audio to be switched on or off, as depicted by the single throw switches in the image above. However, the switches are controlled by logic signals.

Available Wave Forms

VCO1 and VCO2 provide the following wave forms:

VCO3 offers the same waveforms, except an inverted sawtooth instead of the triangle sawtooth mixture. This inverted sawtooth is useful for modulation.

The VCO wave forms can be selected by a 3-bit logic signal.

The noise module offers white noise and pink noise spectra. These can be selected by a logic signal.

VCO1 - VCO2 Synchronisation

UBZR1 VCO1-VCO2 Synchronisation

VCO1 can be switched to "hard" synchronise VCO2. This forces VCO1's frequency onto VCO2 and allows for some interesting spectra when VCO2 is deliberately detuned.

VCO1 - VCO2 Ring Modulation

UBZR1 VCO1-VCO2 Ring Modulation

VCO1 can be switched to "ring modulate" VCO2. This multiplies the VCO1 audio output signal with the VCO2 audio ouput signal and allows for example to generate bell type sounds.

Summing Audio Sources and Filtering

All four modules provide output currents, not voltages. These mix easily at the input of the voltage controlled filter (VCF).

Preparing the Output and Optional Reverb

The VFC output is the input to the "Out" module, which controls the overall volume and has the capability to add reverb.


Each of the four modules has two VCAs each. One of the VCAs is dedicated to the audio signal path, as shown above. These outputs are labelled with the subscripts "0" or "W/P". The other outputs - with subscripts "1" or "P/R" - are used for modulation.

Last change: 2023-07-12
© 2002-2023 Dr. Thomas Redelberger

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