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Section 0

Chroma to Chroma Interface Lead

by Martin Straw [21010093+]

This wiring diagram applies to:

  1. ARP Chroma
  2. Rhodes Chroma
  3. Chroma Polaris

The Chroma to Chroma interface lead looks like an ordinary male-to-male RS232 lead, with a 25-pin D-connector at each end, joined by a shielded multi-core cable.

However, it carries parallel, not serial data, using non-standard wiring conventions.

Do NOT connect pin 5 since this is only used to supply power to small devices, such as the KMX MIDI interface, which plugs straight into the Chroma computer interface.

If the Chromas fail to communicate, or produce intermittent results, first check the SET-SPLIT status as described below, then if this fails, remove capacitor C22 (0.01uF) from the computer interface section of the big I/O board, or replace it with a 100pF capacitor if you are working in an exceptionally electrically noisy environment.

To install the cable, make sure both Chromas are switched off, then connect the cable to the COMPUTER INTERFACE port on the back of each instrument.

When a Chroma is switched on, it defaults to working in isolation, ignoring the other instrument, unless a MIDI interface is connected to the COMPUTER INTERFACE, in which case the Chroma will remember the MIDI settings you have previously defined.

Press the SET SPLIT button, followed by 17 to turn on a performance communication session. This can be done on just one Chroma, to produce a master-slave relationship, or on both Chromas, to create an equal partnership with two-way communication.

This will only cause the keyboard and other performance controls to communicate, which is the normal music working environment.

SET SPLIT followed by 16 turns off the performance communication transmission.

You can also press SET SPLIT followed by 19 to turn on control panel communication, where the Chroma programming and program number selection commands are also communicated and acted upon.

SET SPLIT followed by 18 is supposed to turn off the panel communications transmission, but this often does not work, in which case switching off the Chroma will re-set the instrument to working in isolation, with no transmissions taking place. The system-reset function, initiated by SET SPLIT followed by 50, may also have the same effect, but I have not tried it.

SET SPLIT followed by 20 can be used to transmit the currently active voice patch program to the other instrument, where it also becomes the active program. This program is defined as number zero, so it must be stored in one of the 50 program memory locations, to prevent it from being lost when the next program is selected.

If a MIDI interface is connected, it is also possible to transmit any number of programs, from the current program to the full set of 50 programs in memory, plus being able to operate polytimbrally as well as polyphonically, plus being able to perform automated mixing.