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GKFX-1 - Piezo Subsonic Filter

The GKFX-1 will improve ghost note immunity and enhance tracking with Piezo pickups. However this unit has virtually no effect on GK pickups and guitars with RMC boards newer than 2011/2012 (i.e. Godin xtSA etc.) .
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GKFX-1 contain specially designed filters to improve PCM/COSM tracking and ghost note immunity as well as lowering noise when palm muting.
Most noted effect on GR-55, GP-10 and VG-99 when using Piezo 13-pin guitars.


13-pin GK Guitar input and 13-pin GK Guitar synth output. 13-pin patch cable included (1 meter). GKFX-1 is self-powered by synth unit.

Input jack

The input jack allows you to connect a regular guitar to your synth for COSM processing.
Individual volume control for the guitar jack and the regular pickups.

Send jack
The SEND jack allows you to extract the mix of the two signals to some other device, or connect it to a guitar pedal
and feed it back to the RETURN jack to create a pre-synth FX-loop.
S1/S2 can be controlled by external foot switches.
IN GK 13-pin Guitar input connector
OUT GK 13-pin Roland guitar synthesizer output connector
INPUT High impedance regular guitar input jack

Videos and Images

13-pin DN

A picture showing the IN and OUT 13-pin connectors of the GKFX1


INPUT allows you to connect a regular guitar into your synth (no polyphonic synth effects). The RETURN jack will override the regular guitar pickup sound from the INPUT. This allows you to connect effect pedals between SEND and RETURN jacks.

Send and S1/S2 connections

S1/S2 allows you to control synth S1/S2 using an external foot-switch. SEND allows you to hijack the guitar sound and feed it somewhere else, maybe to guitar pedals and then back to RETURN jack or to another amp.

GKFX-1 Connections Chart

Here's the complete connection chart of the GKFX-1