Updates: April 2017
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GK QuadBoard

GK QuadBoard - 1 input, 4 output 13-pin Guitar Synth Signal Distributor - GKP-4 clone

Features and Specifications:

  • 1 - 13-Pin Roland Guitar Input
  • 4 - 13-Pin Roland Guitar Synthesizer Outputs
  • Optional user configurable GK S1/S2 routing
  • Optional user configurable individual synth output mute
  • Ability to select from guitar GK S-Volume, or max volume
  • Onboard drivers for up to four LEDs
  • Duplicates circuitry of Roland GKP-4: GK S1/S2 diode protection, regulated +5 volt power supply
  • Insert points for Roland EV-5 or 10K control potentiometer for further volume control
  • 6 stainless steel right angle 4-40 mounting brackets for pcb protection and secure mounting
  • Size: 6" (W x 1.75" (D) x 1.25" (H) appx.
  • SOLD OUT!

Videos:


GK QuadBoard 1 input, 4 output Roland GKP-4 Clone

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.

Introduction to the GK QuadBoard, 1-input, 4 output Roland Guitar Synth Signal Distributor:

Quad Board
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.

Filter-Buffer Diagram
QuadBoard with accessories: mounting screws, 6 color-coded conductors, 10 .01uF capacitors, and 16-position ribbon. Click to enlarge.
Standard Format:

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:
TRS Schematic
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
Butterworth Filter
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.

Filter-Buffer Diagram
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:

Photos:

Click on any image for larger view.

Photos Rackmount:

Click on any image for larger view.

Nigel Hardwood purchased a GK QuadBoard, and let me know he was planning on rack mounting the GK QuadBoard. I thought this was a great idea, so I followed Nigel's lead and purchased a blank, 1/8" rack panel on ebay for about $10, including shipping.

Using the cutout pattern posted on this page, I drilled the necessary mounting holes.

This worked out really well. The 1/8" blank panel is really sturdy, and there is plenty of room on the panel to add additional features like synth mute on/off features, and GK select switches.

Frequently Asked Questions:

  • Does the QuadBoard add any latency or delay?

  • No. None of my processors add any delay at all. Like the GR-300 and GR-100, they are purely analog processors that do not suffer from the inevitable latency introduced by digital systems.

  • Will the QuadBoard work with ANY Roland Guitar Controller or Guitar Synth?

  • I have tested the QuadBoard with the Roland GK-3, and the Godin LGX-SA guitar using the RMC pickup system. The Equator also been successfully tested with the Boss GP-10, Roland GR-55, GI-10 and VG-99.

  • Does this unit require any power?

  • No. The QuadBoard gets its power from the connection to the first guitar synthesizer, output "A". This is the same approach Roland used for the BC-13, US-20 and GKP-4.

  • What kind of LEDs can I use with the QuadBoard?

  • I suggest typical 2 volt, 20 ma LEDs. The current limiting resistors for the LEDs are 1K. For the demonstration unit that I built, I used RED and GREEEN Leds ordered from Mouser Electronics.

  • I hear a low-level hum with some patches. Is this normal?

  • In my experience, you are probably hearing a ground loop hum. On some patches, particularly those with a big low frequency eq boost, you can possibly hear a hum, depending on the synths you are using, the guitar, and the patch. Typically these patches involve the normal pickups, or high levels of gain or distortion. This almost never happens with patches that involve only MIDI signals. For the patches used in the video demo, there was no hum whatsoever, but any time you have a large system with multiple paths to ground, ground loops (hum) can happen. Here is a great thread from the V-Guitar forum discussing this issue regarding the US-20.

  • What are the .01 uF capacitors for?

  • The 0.01 uF capacitors are highly recommended to prevent switch bounce for the GK S1 and GK S2 switches. These capacitors connect between the output (signal sent to the attached synth) and the unit ground. The QuadBoard includes ten of these capacitors. At most, you will need eight.

  • Do you have any suggestions for a case?

  • The size case you need really depends on how many features you are planning on adding. For a basic unit, with minimum of add-ons, the BUD case (CU-482-A) looks like good choice: 2" x 8" x 4".

  • What kind of case did you use in the demo videos?

  • I used a Hammond Enclosure, 1455R1601BK. However, I do not recommend this case! As it worked out, there was barely enough room to fit in all the components. I had to do extensive interior metal working to get everything to fit.

  • Where can I find more of the multi-colored jumpers for my QuadBoard project?

  • The QuadBoard uses industry standard 0.01" (2.54 mm) spacing for the jumpers. You can find kits to build your own, though you can also find pre-made bundles of wires on ebay. Since there are male pins on the QuadBoard pcb, you want female connectors. Typical prices are less than $5 for 40 jumpers 8" to 12" in length (20 cm to 30 cm). Here is a good ebay search link.