Roland BC-13 Bus Converter

Introduction to the BC-13:

Towards the end of the original guitar synth series, Roland produced the BC-13. The name is short for "Bus Converter 13." This is a neat little box that converts the 24-pin guitar signals into 13-pin signals. There are three connectors on the BC-13: a 24-pin input connector, a 13-pin output connector, and a 1/4” guitar jack. Operation is simple: plug your vintage Roland guitar in the 24-pin connector, then use a C-13 (13-pin) cable to connect the BC-13 to your favorite 13-pin device. Unless you were using a GK-1, you also needed to run a regular guitar cable from the 1/4” jack on the G-X0X guitar to the 1/4” input jack on the BC-13. Electronically, the BC-13 does several things: the high-output vintage GR signals are conditioned to match the lower level signals found in the new Roland GK-2/2A/3 style pickups. Similarly, the filter knob (CV#1) output is adjusted to match the new Roland standard, and several digital transistors are used to adapt the Mode switch and the resonance knob (CV#2) to new switching functions.

Guitar Controls and the BC-13:

In brief, you loose most of the controls that make a vintage GR-X0X guitar so exciting when using the BC-13! On the other hand, this should not be so surprising, since the current Roland guitar synths have basically nothing more than a volume knob and program switches on them. Anyway, it was the dawn of the nineties, and digital programmability was in, analog knobs and tweaking were on the way out. As a result of this "philosophy" change in design, the BC-13 adapts the vintage Roland control knobs, such as the filter (CV#1), resonance (CV#2) to do more mundane tasks. Here is a breakdown of how the BC-13 translates the controls:

This diagram shows the controls on the Ibanez IMG2010 and various Roland guitars. Notice the layout is basically the same. Also, note the IMG2010 does not have touch plates to activate modulation. The vibrato (or modulation) knob, CV#4, is always active on the IMG2010.

Guitar Knob/Controller	Original Function	BC-13 Function
Volume Knob	Volume	Not Used*
Balance Knob	Guitar/Synth Balance	Not Used
Filter Knob (CV#1)	Filter	Volume
Resonance Knob (CV#2)	Resonance	Guitar - Guitar/Synth - Synth
Whammy bar* (CV#3)	Pitch Bend	Not Used
Modulation Knob/Touch Pads (CV#4)	Modulation	Not Used
Mode Switch "UP"	Mode III	Switch #1
Mode Switch "MIDDLE"	Mode II	Not Used
Mode Switch "DOWN"	Mode I	Switch #2
* The only guitar ever to use the whammy bar, CV#3, is the Ibanez X-ING IMG2010 guitar. Roland notes CV#3 on the schematics for the GR-700 and GM-70, but they never built it into one of their guitars.

Guitar/Synth Balance and the BC-13:

The BC-13 uses the Resonance Knob (CV#2) in a way that is very similar to the Mode switch on the vintage GR-series guitar. But rather than having a three-position switch, the knob has three "zones." The first zone is guitar only, the middle zone is guitar and synth, and last zone is synth only. Confusing? Yes. And you will notice the old Guitar/Synth balance knob is ignored.

The Extra Cable Connection*

This diagram shows the single cable used to hook up a GK-1 to the BC-13, and two cables for the G-Series guitar and the BC-13.

Finally, unless you are using a GK-1, you actually need two cables to be able to control the volume of the guitar with a BC-13. You need both the special Roland 24-pin cable and a regular guitar cable from the 1/4” jack on the G-series guitar to the 1/4” input jack on the BC-13. With this extra cable in place, you can use the master volume knob on the guitar to control the volume of the direct (guitar pickup) sound. Othewise, turning the volume knob on the guitar does nothing, the guitar is always on, at maximum volume.

With the Roland GI-10 this does not matter, since the Roland GI-10 does not have a regular guitar output. With the Roland VG-88 you can program the volume level of the normal guitar. But with the Roland GR-33 you have the guitar sound always loudly playing with your synth sounds.

The GK-1 does basically the same thing, by using a short, 4” cable from the 1/4” output jack on the guitar to a miniature input jack on the GK-1. This way volume for the GK-1 direct (guitar pickup) level is controlled by the passive volume knob on the "host" guitar.

Why do you need an extra cable with a G-series guitar? Originally, Roland designs used a VCA inside the guitar synth (GR-100, GR-300, GR-700 etc.) to change the guitar volume by responding to voltages from the vintage guitar synth controller. The BC-13 ignores all these voltages. Incidentally, to avoid this hassle, I built a stand-alone VCA in the SBC+, which uses the BC-13 style technology and addresses many of the problems mentioned on this page.

Other substitutes for the BC-13 are the BX-13 and DC-13.

A Look Inside the BC-13:

Special thanks to Paul Johnson who provided this look inside his BC-13. The 13-pin connector is on the far left, and the 1/4” guitar input jack is on the far right.

Download the BC-13 Owner’s Manual

Download the BC-13 Schematic from the Yahoo midiguitar User’s Group