Doepfer A-188-9 High Speed VCO at a glance

The A-188-9 module from Doepfer is a so-called high-speed VCO that operates in the range from approx. 15 kHz to 500 kHz octave pure. The main application is the control of BBD delays (A-188-X) for Karplus-Strong synthesis, but also other modules with high-frequency inputs such as eg. Digital Noise or frequency dividers. Basically, the module consists of a precise audio oscillator with a downstream PLL unit (Phase Locked Loop), which operates as a frequency multiplier with a factor of 32. Part of the PLL circuit is a slew limiter that determines how quickly the frequency of the PLL follows the frequency of the VCO. The PLL cannot follow the VCO directly, but a compromise between the ripple of the PLL frequency and the tracking speed must be selected. In addition to its main application as a high-speed oscillator, the A-188-9 can therefore also be used as an additional VCO in the audio range, which has the standard sawtooth, triangle and square waveforms with adjustable pulse width.