Electronic Guitar: Stepping up to Eurorack

A beginner's guide to guitar processing with hardware synth modules
By Michael Ross ,

Last month, I demonstrated how guitarists can achieve a new level of signal processing from the easy-to-use and relatively inexpensive Softube Modular, a software emulation of a modular synth. But what if you want to get those sounds onstage without using a computer?

To run your guitar through a hardware modular- synth, you’ll have to address some issues: The modules don’t have bypass footswitches; they require a case with its own power system (which is not suitable for use on a pedalboard); and the jacks used in the most popular format—Eurorack—are 3.5mm (e.g., minijacks) instead of the standard 1/4" version used by guitarists. Of course, the 5U, Moog-format modules have 1/4" jacks, but their cases are even larger and the overall systems more expensive than Eurorack.

Fig. 1

Up until 2015, Eurorack manufacturer Pittsburgh Modular made the Patch Box Enclosure, a stompbox-style case that not only held several synth modules, but included a guitar preamp and true-bypass switching (see Figure 1). It provided a convenient, pedalboard-friendly way to add synth modules to your stage setup, and it is worth hunting one down on the used market.

A simpler way to add this kind of synth processing to your rig is by using Roland’s AIRA Eurorack-style modules with a Boss ES-5 Effects Switching System. The AIRA modules—Bitrazer (bit crusher), Demora (delay), Scooper (looping with Scatter effects), and Torcido (distortion)—work as standalone processors that can be powered by a wall wart, allowing you to use them on the desktop or pedalboard outside of a Eurorack case. But what about a footswitch?

That’s where the Boss ES-5 comes in. Patching an AIRA module into one of the effects loops on the ES-5 provides a footswitch for dropping the module in and out of the signal path, and the unit can save and recall 200 patch routings. To connect the modules to the ES-5, you will need cables with a mono 1/4" plug on one side and a mono 3.5mm plug on the other (available from your favorite vendor, and easy to make if you know how to solder).

Fig. 2

I put together a rig that combined the Scooper and Bitrazer modules with a main.ace.fx Awdrey Gore fuzz and an Earthquaker Space Spiral delay, all plugged into send/return loops on the ES-5 (see Figure 2). The Scooper records loops of up to 10 seconds, gives you control over pitch, and sends it all through a filter and various Scatter effects to slice and warp the sound. The Bitrazer is a bit- and sample-rate crusher with controls for filter type, frequency cutoff, and resonance. And, of course, both accept control voltages.

Fig. 3

The next step was to find a CV source. In addition to MIDI I/O and a USB port, the Source Audio Reflex Universal Expression Controller has three 1/4" analog expression/CV outputs (see Figure 3). Patched with 1/4"-to-3.5mm patch cables, I used the Reflex to modulate the filter frequency of the Bitrazer and the Scooper, as well as control the Scooper’s Scatter effects. Although I didn’t have a pedal switch to start and stop loop recording, the ES-5 let me run the Scooper in parallel with my direct signal, so I could play along with the stuttering, fragmented loops, which was inspiring. The Reflex Expression Controller also offers five LFO waveforms, which I used for rhythmic filter sweeping, controlling the speed from the pedal.

Sure, there are effects pedals that do similar things, but the abundance of CV inputs on a synth module gives you greater flexibility and a sound that sets them apart.

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