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MKC-1

  Photo 
of MKC-1 circuit board

Introduction

The MKC-1 provides a means to add limited MIDI control to older synthesizers by interrupting the electrical path between the keyboard switch assembly and the synthesizer control board. MIDI note-on and note-off messages that are received will play corresponding notes on the synthesizer. Keys pressed on the synthesizer keyboard will produce MIDI note-on and note-off MIDI output. If the local control option is enabled, the synthesizer will also play notes normally. If local control is turned off, the synth keyboard will only produce MIDI output, but will not play notes on the synthesizer. Local control can be enabled or disabled with a MIDI command, or by a jumper (or wired toggle switch) on the MKC-1 circuit board.

A jumper option also can be used to enable or disable MIDI OMNI mode. With OMNI mode on, the MKC-1 will respond to note and control messages on all 16 MIDI channels. When OMNI mode is off, the MKC-1 will only respond to messages on the MIDI channel selected by the DIP switch.

The MKC-1 is specifically designed to work with connectors and keyboard matrix layouts used by Oberheim synthesizers. It will work with the OB-SX, OB-X, OB-Xa and OB-8. The MKC-1 operates over a range of 64 MIDI notes starting with MIDI note 36 and is not velocity sensitive.

For use with the Sequential Circuits Prophet 5 synthesizer, a special inverter board is used to produce the correct logic and wiring arrangement.

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Installation

Turn off the synthesizer power before starting the installation.

The MKC-1 has 16-pin IC sockets that are used to connect ribbon cables to the synthesizer. The ribbon cables have a stripe along one edge that indicates the cable orientation. The stripe should always go on the side of the socket with the notch in the end.

The sockets labeled, KEYBOARD IN and KEYBOARD OUT intercept the synthesizer keyboard signals. The original synthesizer keyboard cable should be unplugged from the synthesizer main circuit board and plugged into the MKC-1 KEYBOARD IN socket. A new ribbon cable (supplied with the MKC-1) connects from KEYBOARD OUT to the keyboard socket on the synthesizer main board.

Power for the MKC-1 is taken from any convenient 16-pin digital IC on the synthesizer board. This usually turns out to be a 74C42 or 74LS42 located somewhere near the keyboard socket. Remove this 74C42 IC and re-install it on the MKC-1 board in the socket labeled, J1. Connect the second ribbon cable supplied with the MKC-1 from socket J2 to the now vacant socket on the synthesizer board. Be sure to orient the IC and cables correctly.

Two MIDI jacks are supplied with the MKC-1 and can be mounted in any convenient location. The MIDI jack cables connect to the MKC-1 with Molex connectors that are keyed for correct orientation. The MIDI IN jack should connect to the MIDI IN Molex connector on the MKC-1. The MIDI OUT jack can be connected either to the MIDI OUT connector, or the MIDI THRU connector if you don.t intend to use the synthesizer keyboard to produce MIDI out.

The MKC-1 board can be mounted in any convenient location using the standoffs supplied. When using the stick-on nylon standoffs, be sure that the mounting surface is clean and dry before adhering them.

If everything is connected correctly, the LED on the MKC-1 should light up when the synthesizer is turned on, and the synthesizer keyboard should work normally.

Operation

A four-position DIP switch on the MKC-1 board sets the MIDI channel for send and receive. The following chart shows the switch settings for the available selections:

SW4 SW3 SW2 SW1 MIDI Channel
DOWN DOWN DOWN UP 1
DOWN DOWN UP DOWN 2
DOWN DOWN UP UP 3
DOWN UP DOWN DOWN 4
DOWN UP DOWN UP 5
DOWN UP UP DOWN 6
DOWN UP UP UP 7
UP DOWN DOWN DOWN 8
UP DOWN DOWN UP 9
UP DOWN UP DOWN 10
UP DOWN UP UP 11
UP UP DOWN DOWN 12
UP UP DOWN UP 13
UP UP UP DOWN 14
UP UP UP UP 15
DOWN DOWN DOWN DOWN 16

The MKC-1 will normally receive data on all 16 MIDI channels (OMNI mode). OMNI mode can be turned off with a MIDI control command, in which case the MIDI receive channel will be determined by the switch setting (above).

The MKC-1 supports the following standard MIDI commands. All byte values are shown in hexadecimal, with .x. representing (MIDI channel . 1) and .XX. meaning .any value from 0 to 7F..

Local Control ON/OFF (received only)
	Bx 7A 00 = Set local control off
	Bx 7A 7F = Set local control on

OMNI mode ON/OFF (received only)
	Bx 7C 00 = Set omni mode on (receive on all MIDI channels)
	Bx 7D 00 = Set omni mode off (receive on channel set by switches)

All Notes Off (received only)
	Bx 7B XX = Turn off all notes

Note On/Note Off (transmitted and received)
	9x   = Note on
	8x   = Note off
(Note number range = 24 to 63.  Transmitted velocity = 40.)

Active Sensing
	FE = Active sensing (received only)
 
A version of the MKC-1 for the Sequential Circuits Prophet 5 is available. See installation photos here.

Ordering Information
All orders must be prepaid by check, money order or PayPal. You may use the PayPal shopping cart (below), or you may make your payment in care of pjwhite@electrongate.com. Include your shipping address and specify that payment is for the "MKC-1".

Contact Paul J. White for more information.


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MKC-1 Kit for Oberheim synthesizers $129  
MKC-1 Kit for SCI Prophet 5 $164  

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