FSI (Footswitch Interface)
Foot controlled gate and expression control module

At 4HP, the FSI module is a small-footprint controller interface useful for both live performance and recording. The expression pedal input allows you to send up to 3 control voltages ranging from 0-10V, ±5V and ±2.5V anywhere in your system, with a fourth outputting the inverse of the selected voltage. This lets you sweep filters, crossfade between patches and control dry/wet mixes, all while your hands are busy turning knobs or plucking at strings. The footswitch portion of the module outputs three 5V gates with a fourth outputting the inverse of that gate. This function is particularly useful for recording into samplers, activating loops, pinging filters (turning the FSI into a kick drum pedal), or tapping in a clock.

We recommend the Yamaha FC-5 Foot Switch, and the Moog EP-3 Expression Pedal (with standard polarity), though most expression pedals with a potentiometer output at the Tip of a TRS cable will work. The FSI has a polarity jumper on the back of the module, in case your pedal doesn’t have one of its own. The FSI was designed with a normally “closed” passive footswitch in mind (such as the FC-5), but keep in mind that the inverting output will function normally with an open switch, so most pedals can be accommodated.

A small batch is currently available. Email me at marc@fkmg-circuits.com for direct sales, or click the button above to head over to our Reverb storefront.

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