Doepfer A-110-4

This analog VCO is well versed in the art of deep and beautiful thru-zero frequency modulation, allowing the frequency to stop when CVs with 0V are applied and even to go backwards when modulated with negative CVs.
The term “quadrature” refers to simultaneously available sine and cosine waves at individual outputs. The VCO is sine based i.e. no waveshaping is used to derive the sine; for that reason the sound is really clear and shows a minimum of distortion and overtones.
The module has two control sections:
The exponential section consists of the XTune control, the 1V/Oct input and the XFM input with the corresponding attenuator XFM.
The exponential control voltage is the sum of these three voltages. The linear section consists of the LTune control and the LFM input with the corresponding attenuator LFM. The linear control voltage is the sum of these two voltages.
The main advantage of the A-110-4 compared to other Thru Zero VCOs is that the design uses a sine/cosine core. The sine/cosine waves are not derived from other waveforms (e.g. sawtooth or triangle) by means of waveshaping. Rather the sine and cosine waves are the core of the VCO which results in very pure waves with a minimum of distortion and overtones.
With it’s both control possibilities, linear and exponential, as well as it’s thru-zero ability, the VCO is perfectly suited for all types of FM applications.
inputs: 1V/oct, exponential FM (XFM), linear FM (LFM)
outputs: sine, cosine