Introduction to the GK QuadBoard, 1-input, 4 output Roland Guitar Synth Signal Distributor:
Roland GKP-4 Clone with Expansion Options:
The GK QuadBoard is a one input, four output Roland guitar synth signal distributor. Electronically, the QuadBoard is essentially a clone of the long discontinued Roland GKP-4.
However, the QuadBoard differs in several key areas from the GKP-4. Most significantly, the QuadBoard provides a dedicated control voltage buffer for each synth. This means that the user can individually mute each output, much like a Roland US-20 does.
In addition, rather than using tiny micro-switches in the style of the GKP-4, the QuadBoard uses internal jumpers to allow the user to configure, modify, or expand the QuadBoard to meet their individual needs.
For do-it-yourself experimenters, the QuadBoard includes the parts needed to start modifying the design to include both outputs mutes, and independent GK S1/S2 signals for each output.
|QuadBoard with accessories: mounting screws, 6 color-coded conductors, 10 .01uF capacitors, and 16-position ribbon. Click to enlarge.
To accommodate the high level of customization and provide real affordability, the QuadBoard ships with mounting hardware, but no case. Jumpers are installed to send the same GK Synth Volume and GK S1/S2 commands to every synth.
One sixteen position ribbon, and 6 color-coded conductors are included to jump start customization. Also included are 10 .01 uF capacitors, recommended for use if you are building your own GK S1/S2 switching system. The unit is fully tested and ready to go.
GK S1/S2 Switching:
|Diagram for wiring a TRS connectors to the GK S1/S2 circuit. Click to enlarge.
While the original GKP-4 used micro-switches to turn GK S1/S2 commands on or off, the QuadBoard has eight jumpers in the GK switch bank. Two jumpers for each output, representing GK switch 1, and GK switch 2. To disable GK commands for any output, just remove the associated jumpers. You can also mix and match, for example, sending only GK S1 to the first synth output, and GK S2 to the second synth output.
For the DIY, do-it-yourself, guitar player, you can easily add you own GK S1/S2 switches. The QuadBoard ships with a sixteen position ribbon cable that can be installed in place of the GK S1/S2 jumpers. In this example, the ribbon cable has been wired to four, TRS, tip-ring-sleeve, 1/4" jacks.
With nothing plugged in, the same GK S1/S2 commands are sent to each synth output. Or, you can plug in a Roland FS-6, or similar, foot switch to generate new, independent GK S1/S2 commands. Any simple on/off foot switch will work. If you just want to disable the GK S1/S2 commands from the guitar for any specific output, simply plug in a dummy TRS jack. Or course, these are just examples. Alternatively, you could easily wire in dedicated foot switches or pushbuttons as well.
GK Synth Volume
Typical synth mute with LED on/off wiring. Click to enlarge.
There are even more options for GK Synth Volume commands. The QuadBoard provides access to the GK Synth Volume signal at two points: before and after the control voltage buffer amplifiers.
Before the buffer amplifier, you can select from either the GK Synth Volume signal from the guitar, or the onboard, regulated +5 volt supply. This 5 volt supply can be used to set any synth to maximum volume. This is same design used in the GKP-4.
After the buffer amplifier, there are a six open jumpers. These indicate two ground points, and four mutes points for each synth output. Connecting any of the synth mute pins to ground mutes the respective synth output. Check out the video below for an example of a QuadBoard wired to individually mute synth outputs A, B C, and D. Any kind of switch will work, a simple foot switch, or a toggle switch.
Additional Volume Processing (Roland EV-5)
After the mute pins, there are four more jumpers in place that allow the user to individually reroute the GK Synth Volume signal. This is designed so that a basic 10K control pot, or a Roland EV-5, can be inserted to control the volume of each synth individually.
So you can mix and match volume control from the guitar, or volume control from a EV-5 pedal or additional control pot.
Power Supply Section:
The +5 volt power supply is accessed by a dedicated pin in the power supply section of the board.
Circuit board connect points (pdf)
The power supply section also includes drivers for up to four LEDs. By using a SPDT, single pole, double throw foot switch, you can easily wire up mute switches with LEDs for the QuadBoard. These switches mimic the synth mute functions in the Roland US-20.
Go one step further, and include four SPDT toggle switches for selecting between the guitar synth volume and maximum 5 volt volume, Now you have a super hybrid GKP-4/US-20, combining the best features of both products.
Construction and Installation:
All the hardware needed to mount the QuadBoard is included. The QuadBoard has been designed for durability and reliability. A close look at the Roland 13-pin connectors show metal flanges to mount the 13-pin connector against the case.
The CUI 13-pin connectors do not have these flanges, so instead there are six stainless steel right angle brackets installed on the QuadBoard to make sure the QuadBoard stays securely in place, and to protect the circuit board.
With up the five cables connector to the circuit board, the printed circuit board needs to be secure, and there also needs to be adequate room between 13-pin connectors to easily plug and unplug the cables.
The QuadBoard is 6" wide, 1.75" deep, and approximately 1 1/4" in height. The board will easily fit in a number of small, rebuilt enclosures.
Links to more information: