FM OP

Through-zero VCO FM operator

This 4HP module is a thru 0 VCO using the SSI2130 chip. It is designed as an FM operator as per the concepts delivered by John Chowning, so for best results 2 or more are needed (get 6!), along with suitable EGs and mixers. The NLC Valmorification (VC EG) and 4HP Mix are intended as support modules to develop an all analogue FM system. It contains the oscillator and VCA, the EG must be patched in. The thru-0 oscillator has a good variety of controls – control voltage, frequency modulation, phase modulation and hard sync.

The module only has a sine output as per a standard FM operator, although it generally spits out some very complex waveforms. I rarely do any further processing to the signal, such as VCFs or wave folding, there is enough going on.

Before going too far, please check the size and datasheet of the SSI2130 at https://www.soundsemiconductor.com/ . It is tiny and will be extremely difficult to solder by hand, much better to use solder paste and a hot air gun or a reflow oven. Also the circuit requires quite a few unusual resistor sizes that need to be obtained from Mouser or similar. This is not a regular NLC design, where all the resistors are just 1k, 10k and 100k. There are a few other components that have never been used on NLC modules before as well, nothing particularly rare or expensive, just probably not in your stash.

Thanks to Neil Johnson of Sound Semiconductor Inc. for his support and advice in developing this module.

https://www.nonlinearcircuits.com/modules/p/fmop