A format for plug-in circuit cards that can mount in a modular synth carrier module, developed by Black Market Modular. ColourCV is based on a format called Colour (note British spelling), which is an open-source format for plug-in modules for 500 series pro audio processing equipment, developed by the pro audio DIY community. The Colour format provides for a circuit board of 3" (76.2 mm) length and 1.4" (35.6 mm) width, with an allowable height of about 1/2" (14 mm) above the board for components.
In the original Colour format, the card connects to the carrier using an 8-pin connector. The connector provides for one audio in, one audio out, ground, +/- 16V power (the 500 module standard), and three pins to drive an RBG LED on the carrier's panel. By setting resistors in the LED drive lines, the card can cause the LED to light up in any desired color. The intent is that the LED color provides a general idea of the card's function, although there is no standard for what different colors represent.
Black Market added to the standard by changing the 8-pin connector to a 14-pin. Two of the pins are used to supply Eurorack-standard +/- 12V power, so that cards based on Eurorack circuitry can work with the voltage that they were designed for. (The ColourCV carrier module does also provide the 16V power.) Four pins are used to supply up to four control voltages, supplied from the carrier module. Standard Colour cards can plug into the 14-pin connector and will work, although of course they cannot use the control voltages. A range of Color cards are available from various pro audio vendors.
The 500 module standard is that audio is transmitted on the case's backplane. The Black Market carrier, however, brings the audio ins and outs for each card out to the front panel, for patching. A VCA is available for controlling the audio input level for each card. The four control voltage inputs are also patchable.
A few possible complications exist. The ColourCV format does not provide 5V power to the cards. Normally, synth circuits use 5V power for LEDs and digital logic. The former is not a concern for the cards since they contain no indicators of their own; however, for digital logic, it may be necessary for the designer to use an onboard regulator to reduce one of the higher voltages to 5V. Another potential issue is that the carrier provides all four control voltages to every card that is installed. If multiple cards are installed, there may be confusion as to which control voltages are intended to be used by each card. It may be necessary tor cards to provide moveable jumpers, or some similar mechanism, to avoid conflicts in the use of control voltages between cards.