This Module is a prototype or in a concept phase.
A-1?? QVCO prototype
The picture shows the preliminary front panel of the planned Thru-Zero Quadrature VCO (QVCO). The term "quadrature" means in this connection that the oscillator outputs sine and cosine waveforms simultaneously. The term "Thru-Zero" means that even "negative" frequencies are generated. But this a bit a misleading term as negative frequencies do not really exist. "Negative" means in this connection simply that the polarity of the waveform is reversed (thru-zero pictures will follow as soon as our pc-based oscilloscope is repaired).
The module will have two different control modes: exponential and linear. The exponential control mode is known from most of the VCO and VCF modules. The most common exponential scale is 1V/octave. In this mode thru-zero is not possible as the exponential function cannot become negative. In the exponential mode the lowest frequency is about 0.3Hz (i.e. period time ~ 3 seconds), the maximum frequency is about 5kHz for the prototype. In the linear control mode the relation between control voltage and frequency is linear: e.g. 0V = 0Hz (i.e. oscillation stops), 1V = 1kHz, 2V = 2kHz, 3V = 3kHz and so on. In this mode thru-zero is possible. The frequency range for the prototype is about -5kHz ... +5kHz.
After all the QVCO is a 12dB filter circuit in self-oscillation, optimized for constant output level over the entire frequency range (for many filter circuits the amplitude varies with the frequency in self-oscillation). This is why the module can be switched between VCO and VCF. In the VCF mode the audio input is used. The sine output becomes the low pass output and the cosine output becomes the band pass output. In the VCO mode the audio input is not used and the resonance control defines the output level and has also an effect on the waveforms. From about 2 to 7 the module generates low distortion sine/cosine waves with adjustable level. Beyond 5 the waveforms change more and more into triangles, i.e. odd harmonics are added. In the VCF mode the resonance control works as usual and the audio input .
