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Instrument Interface Module — Bring FX and Instruments Into Your Modular Synth World
Integrate Your FX Pedals and External Instruments With Ease!
The Instrument Interface Module lets you connect external effects pedals, processors, or instruments—such as electric guitars or synths—seamlessly into your modular synthesizer system.
2 FX Send Outputs attenuate modular-level signals down to line or instrument level.
3 FX Return Preamps amplify incoming signals back up to modular synth levels.
This versatile module works as:
An external input amplifier for guitars or keyboards.
A way to use stompbox FX pedals with your modular setup.
A bridge between modular-level gear and traditional instruments.
How It Works
Modular synthesizers operate at much higher signal levels than most instruments or effects pedals. Directly connecting them causes two main issues:
Signal overload at the pedal input due to excessive voltage.
Weak return signal from the pedal that isn’t strong enough for modular inputs.
To solve this, the Instrument Interface Module:
Attenuates the outgoing modular signal by a set ratio (default: 20:1).
Then boosts the return signal by the same ratio, restoring it to modular-level strength.
The module uses a non-inverting preamplifier design with a gain of 20x, suitable for a wide range of synth and pedal signal levels. Input impedance is approximately 150kΩ. For fine-tuning, gain can be adjusted by modifying key resistor values (e.g., increasing the 470Ω resistor reduces gain).
Construction Notes (For DIY Builders)
Before Assembly:
Inspect the PCB for etching faults (shorts, gaps).
Sand edges if necessary to remove splinters or rough areas.
Assembly Order:
Begin with resistors.
Install IC sockets (if using).
Move to taller components last.
Important:
Take extra care with the orientation of polarized components—electrolytic capacitors, diodes, transistors, and ICs.
You can play around with the voltage divider resistors on the FX Send sections, Or OMIT R3, R6, R15, and R16 and just use TR1 and TR2 to manually trim your levels to what you prefer! Or a combination of both if you want!
1/4” Jack Pinouts:
J1: Pin 1 (Square pad) GND
J1: Pin 2 Tip
J1: Pin 3 Normal
J10: Pin 1 (Square pad) GND
J10: Pin 2 Tip
J10: Pin 3 Normal
J11: Pin 1 (Square pad) GND
J11: Pin 2 Tip
J11: Pin 3 Normal
J12: Pin 1 (Square pad) GND
J12: Pin 3 Tip
J13: Pin 1 (Square pad) GND
J13: Pin 3 Tip
** 4U Modular is a term used for the format most commonly known as “Serge Format” or “Loudest Warning Format”. Out of respect for the ever growing format, 4U Modular is the easiest way to refer to it. More Specifically it refers to the panel height and mounting hole style. 4U Modular will patch up just fine with other 4U "Serge" formats such as "Random Source", but it will not mount in RS boats or Buchla Boats (or power off Buchla power for that matter). An info page about this will be added to the website soon to make this a lot more easy to understand.
DIY info:
LGE060 Main Board Bill of Materials
LGE060 Main Board Schematic
LGE060 Main Board Designator Layout
Mechanical Parts BOM generally required for building Low-Gain Electronics Modules
Details:
PCB Size: 6” x 2”
Current Draw: TBD