the GK-3B will only work if you also have a Roland GR or VG unit. It is not a MIDI device in and of itself, but simply a pickup designed to transmit a signal directly to a proprietary Roland GR (synth) or VG (effect) unit such as the GR-20 or VB-99. They also make a unit that will convert the signal to MIDI signal for use with a regular rack synth (or keyboard) Unless you have one of those units, the GK is useless.
Like Jeremy said... you are much better off using a keyboard.
The Roland units are EXPENSIVE... awesome, extremely versatile and powerful, but expensive.
DX
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Aerodyne Jazz Deluxe
Pod X3 Live
Genz Benz GBE250-C 2x10
Acoustic 2x12 cab