Guitar Pedal FX Interface
UniFX is a compact and flexible effects interface that interconnects guitar pedals and electronic instruments with eurorack synthesizers. The module re-scales audio levels, offers voltage-control over the dry/wet mix, and uniquely allows for the primary and effects signals to swap sources.
- Single-channel effects loop with bi-directional level conversion
- Routes eurorack thru pedals or instrument thru eurorack
- Effects mix crossfader with CV input
- Feedback capable and functional as VCA
UniFX makes it easy to process eurorack audio signals with pedals, or to process external instruments with eurorack modules. Essentially, it is a level-scaling effects loop. The module has two pairs of mono IN and OUT jacks for signals—3.5 mm at eurorack-level and 1/4-inch at pedal-level. The slide switch labeled PEDALS-EUROFX swaps which jacks are used as the primary input/output and which are the effects send/return.
To process eurorack audio signals with guitar pedals or outboard gear, use PEDALS mode. The eurorack source signal is patched thru the 3.5 mm IN and OUT jacks, while any pedals are connected to the 1/4-inch IN and OUT jacks.
To process line-level instruments or guitar with eurorack modules, use EUROFX mode. The line source signal is patched thru the 1/4-inch IN and OUT jacks, while any effect/filter/etc modules are connected to the 3.5 mm IN and OUT jacks.
Audio level scaling is approximately ± 12 dB, appropriate for most pedals.
The FX MIX parameter is a variable crossfader controlling the dry/wet balance of the input and effects return signals. The amount of effects mix is indicated by the WHITE LED. With the knob turned all the way down, only the input signal is heard from the OUT jack and the LED is off. Alternately, with the knob turned all the way up, only the effects return signal is heard and the LED is fully illuminated. The center position produces a 50/50 mix.
This parameter may also be automated using the CV input labeled MIX, wherein the knob position is used to bias the incoming control voltage. The full range of the parameter is 10 Vpp, so a typical LFO of ± 5 V will fully sweep the FX MIX up and down if the knob is in the center position.
VCA & Feedback Effects
Because the circuit is VCA-based and DC-coupled, UniFX may also be used like a typical VCA module for both audio and control voltages. The only difference is that the control input works in reverse—as the voltage is increased, the signal is reduced. Simply run the primary signal through the 3.5mm IN and OUT jacks, connect nothing to the 1/4-inch jacks, and select PEDALS mode using the switch. Turn the FX MIX all the way up to have no dry signal, and apply a negative going control voltage to the MIX CV input.
Additionally, due to UniFX’s switching effects loop topology, feedback effects can be easily achieved. Just slide the switch into the “wrong” mode, and turn the FX MIX parameter down to increase the amount of the effects return being fed back into the effects send. The MIX CV input can also be used for experimental voltage-controlled feedback effects.