Retro Mechanical Labs GPI

Retro Mechanical Labs GPI

The RML “GPI” or (Guitar Pedal Interface) is designed to bridge guitar pedal world with modular synth world. An 8HP eurorack unit with two attenuators for sending a reduced signal to guitar pedals for better dynamic response and two pre-amps that boost that lower volume signal (from guitar pedal) back to eurorack levels. Each pre-amp splits the output signal into two patchable outs for creative routing options into other modules.

• 2 units per module allowing for use with stereo pedals.

• Use the pre-amps to boost other low level signals like line level gear.

• Use the attenuators to reduce control voltages being sent from other modules

• Plug your guitar right in to the GPI using 1/4 to 1/8 cables

• LEDs flash in response to the signal being boosted by the pre-amps. A good indicator on how hard your driving the signal.

• Very low power consumption.

A couple of random thought on the design:
There are many “Send and Return” modules available, all mono. With this one I wanted to make something available that could handle stereo pedals (or line level gear) without having to buy multiple units. Along the way I decided that having 1/4″ cables hanging off the eurorack seemed bulky and cumbersome so I went with 1/8 (3.5mm) jacks. 1/4 to 1/8 cables have the same construction as eurorack cables and can be found at a very affordable prices.

After building the first prototype I quickly found that just using the pre-amp worked great for boosting the Buchla audio level up to normal levels compared to my DPO and Lifeforms. Routing my Moog though the attenuation and into the pre-amp worked like a charm. Having this simple but versatile tool in my rack has definitely been enjoyable. Not only can I now use all those old guitar pedals with my system, but external keyboards I hadn’t considered are now an option.