MIDI Breakout Box

Breakout Box for the Roland GK system

The Roland GK system also used by RMC, Godin and others is very much a plug it in and rock unit, but what if you want a little more out of it, even to know its basic principles of operation?

Unfretted is about to unravel all of that, pass on some tips, some suggested circuit diagrams, and where to source the plugs and sockets.

If it all gets too technical we will try via e-mail or The Forum to provide you with more answers than questions.


If you blow anything up, its your fault, even if we told you to do it. This article does not contain all the information you need to safely carry out suggested tasks. Even so we strongly discourage the wearing of nylon clothes when using a soldering iron. Do not play the guitar in the bath.


While the RMC breakout box looked really nice, funds were getting low here at Unfretted, so economics triumphed over lethargy and we decided to build our own.

The basic requirement was to provide 6 jack sockets on which the sounds from individual strings would be output.

Then we thought a bit more and it seemed like a good idea to also provide a jack socket output for the mixed string output of the guitar.

One of the things that you really need control over when using multiple effects units is being able to back off the volume. So we threw in a socket for a volume foot pedal, although this could very well be mounted as a volume control knob.

Finally we added the ability to “mute” individual strings on the MIDI side, so that if you are running analog signals from strings 5 & 6, you can mute these strings on your GK device.

Making any sense?

If not, I’m sure you know someone with a soldering iron.

Skills involved

Its always difficult to advise whether or not to embark on a project. Most of what is within this article presumes a prior knowledge of electronics.

The idea is to give you building blocks of information, so that you can design the box that fits your requirements.

If you have never soldered before, or don’t know your caps from your trannies its time to find a friend with an anorak.

Alternatively, if you have already dabbled in the dark interior of a guitar’s cavity, this might be just the thing to stretch and improve your skills.

The only thing requiring a fair amount of skill is soldering the 13 pin din plugs, on a scale of one to ten you need a six for this, where a seven would be the level required to get a job.

Now you are feeling cocky, go back and read the warning at the top of the page.

breakout box roland GK

Unfretted’s Breakout Box

breakout box front panel

Breakout Box Front Panel

Four circuits of the breakout box

The breakout box actually consists of four distict circuits, or sections. These are; The Breakout, The Isolator, The Power Indicator, and The Volume Control. You could include all of these as in Unfretted’s breakout box, or you can pick and choose which features to incorporate.


The Breakout Circuit

This is the simplest possible breakout circuit, if you want to access all six strings individually, and the mix (normal guitar) output. It will work fine with RMC pickups providing your on board guitar battery is OK.
(On Godin and similar you will have to plug a dummy jack into the normal guitar input to wake the battery)

It will not work with GK2A / GK3A type pickups or Roland ready guitars as you need to power the GK unit. This is typically +7 volts and -7 volts, but the spec sheet for the op amp gives a max rating of +/- 19 volts so a simple circuit with 2x PP3s will do fine for this.

breakout box pp3 power supply


This is a simple circuit, but there’s plenty mistakes to be made. Ensure the voltage polarity is correct before attaching to any GK / RMC pickup. Measure it with a meter, check the polarity and then check it again. And then get a mate to check it. If its wrong there could be smoke, grief, and a right old telling off when Mr Roland gets his GK back for repair.

The switch is to isolate the batteries when not in use. While this should always be connected to a guitar, NEVER connect this end to any equipment. There is a chance of a loud bang and a laundry bill. You have been warned.

breakout box isolator circuit

The Isolator Circuit

All the above circuit does is break the signal path for one or more strings. Even so this is amazingly useful as a stand alone circuit if you are running multiple effects units.

Switches are shown in the “off” position. All other signals are passed through the unit.

breakout and isolater circuits

Breakout and Isolator Circuit Combined

This is a combination of the breakout and isolator circuits and is what we put into Unfretted’s red box. The guitar is always connected to the individual jack sockets, strings 1-6 and the mix, but there is the option to mute or isolate individual strings and the mix being passed on to other equipment such as MIDI or VG88, VG99 and GR55 type devices.

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