MIDI et al

MIDI, RMC and the Roland GK system

Jahloon – 2004

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 email 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.


Since the advent of MIDI (Musical Instrument Digital Interface) us guitarists have wanted to be in on the act. Why should keyboard players have all the fun?

The main obstacle to MIDI on guitar has been the way the MIDI signal is generated. On a keyboard it is simple, you press the key, you generate a “note on” signal, you release the key and you generate a “note off” signal.

What a MIDI generator for guitar has to do is quite complex, first it has to detect that a note is being played, then convert the pitch of the note so this information can be sent as a “note on” signal. As the note decays there is a point where the MIDI generator has to decide to send a “note off” signal. In addition, if the guitarist bends a note, the appropriate MIDI pitch bend signal has to be sent.

Now if this process didn’t seem quite complex already, there is a hitch. You can only do this with one note at a time, more than one note would totally confuse the pitch to MIDI convertor. So the solution is simple, use a MIDI convertor for each individual string. At this point conventional guitar pickups go out of the window, they do six strings at a time. What you need is a pickup with six individual outputs, one for each string, what we call in the trade a “hex” pickup. (I think hex is Latin for six)

The output from commercially available hex pickups is quite low, so they all have a small pre-amp circuit located close to the pickup. In the case of the Roland hex pickup this is either a GK2A or GK3A, and for RMC equipped guitars (Godin, Brian Moore etc.) it is a small pre-amp board located inside the guitar.

What most of these controllers offer via a single 13 pin connector is six individual string outputs, a master output – either a mix of the six strings or a through signal from the guitars normal electronics, a MIDI volume signal – via a volume control, and two control switches – usually up/down patch selection.

Even though these hex style pickups are intended for MIDI implementation, there are now products that use the six individual string outputs to implement guitar modelling and the individual processing of single strings for effects such as harmonists and instant alternate tuning. The Roland VG88 and its predecessor the VG8 being the best known.

What has actually been handed to us guitarists is very interesting, yes we have MIDI, yes we have modelling, but we also have a system giving us signals from each string individually. Imagine taking each string through a different effects box, or sending alternate strings to different sides of the stage. Or setting up drone strings to improvise over?

There are two ways of doing this, you can purchase the RMC fanout box, a fine unit but priced at $395 US. That’s quite hefty if you have to pay post, packing and duty to Europe. Second method is you can build your own. Not too difficult as we will be building one ourselves over the next few days. Check out Unfretted’s Hexaphonic Breakout Box. We will be including all the info to build a custom job to your own specification.

Roland 13 pin system:

This carries six individual signals from the hex transducer AND a single audio feed from the guitar’s normal electrics.

If you add a GK pickup there is a flying lead which plugs into your normal guitar jack.

Pinouts & wiring colours, 13 pin DIN cable

Pinouts for the 13 pin DIN connector used with the Roland VG8, VG-88, GR1, GR9, GR20, GR30, GR33, GR55, GP10, GR50, GI10, GI20, GKP-4, Boss DC-20G, WP-20G, Roland Ready Strat, Axon AX100, Yamaha G50, G1-D, Ibanez RG470GK, Brian Moore Guitars + lots of others.

The Roland cables are good quality 13 core, with a braided copper screen

The pins, signals and wire colours are as follows:

1 –   String 1 – Brown
2 –   String 2 – Blue
3 –   String 3 – Grey
4 –   String 4 – Orange
5 –   String 5 – Pink
6 –   String 6 – Purple
7 –   Normal pickups – Green
8 –   MIDI volume – Yellow / Stripe
9 –   Unused on GKA2- Yellow (used on GKA3)
10 –  Switch 1 – Red
11 –  Switch 2 – White / Stripe
12 –  +ve supply – White
13 –  -ve supply – Black

These were taken from a Roland cable manufactured in 1998.

Cables do vary and we have also seen the following colours used:

1 –   Red
2 –   Pink
3 –   Yellow
4 –   Green
5 –   Light Green
6 –   Orange
7 –   Light Blue
8 –   Blue
9 –   Grey
10 –  Brown
11 –  White
12 –  Black
13 –  Purple

One medium quality cable you may come across with a 13 pin DIN connector was used by the Atari ST computer. (For the monitor we think) This was not a 13 core cable, but a 12 core cable, the cable screen was wired to pin 13:

1 –   Purple
2 –   Grey
3 –   Dark Green
4 –   Blue
5 –   Pink
6 –   Turquoise
7 –   Red
8 –   Brown
9 –   Yellow
10 –  White
11 –  Orange
12 –  Black
13 –  Screen

To modify this cable for GK use, first remove the screen from pin 13 and attach to the metalwork of the plug itself. Disconnect the yellow wire from pin 9 and wire to pin 13.
(Don’t forget to do this at both ends)

This cable would be OK connecting equipment together but the plug is non-locking, so take care if using with an instrument.

13 pin DIN sockets and plugs

Well you know if you have tried, these are devilishly difficult to get hold of.

Medium quality non-locking plugs are available in the UK from Maplin order code JW95D.

High quality plugs and sockets are available from other suppliers.

Roland GK2A, GK3A

Essentially, these are add on units, The GK2A has been around since at least 1997 and late in 2004 the GK3A made an appearance.

Installing either of these on a guitar requires a little skill and patience to set them up to perform anywhere close to RMC equipped guitars.

Having both of these units gives us a little insight; we don’t see much advantage of the GK3A over the GK2A – just easier to fit, but looks and feels cheaper, plus the main switch is a pig to get used to. The GK2A’s switch to control output was very easy to flick while playing, the GK3A isn’t, physically it is more difficult, a casual glance doesn’t let you know what position its in.

Hopefully the price for the GK2A will drop when supplies of the GK3A are more dominant, discontinued bargains waiting we hope!

Jahloon's Fretless Baritone GuitarFretless Baritone fitted with Roland GK2A

More DIY Projects

MIDI Breakout Box