ROLAND MPU-104

via this auction

"NEW OLD STOCK Roland MPU-104 MIDI Input Selector. It has never been sold. Purchased by us, M.E.S. Music Equipment Sales Ltd., as an authorized Roland dealer in May 1985, it was somehow overlooked and remained on a shelf for 23 years. The MIDI outputs of up to 5 MIDI devices can be connected to the MIDI inputs of the MPU-104 MIDI Input Selector. The THRU MIDI signal is connected to the destination (computer, sequencer or sound module) MIDI input socket. The desired MIDI device is selected pushing one of the 5 front panel buttons. A red LED indicates the active button. Only one Select Button may be activated at a time... If more than one button is accidentally selected, the lowest number will have priority... The MPU-104 measures 8-9/16" Wide x 1-13/16" High x 6-3/16" Deep and is a standard half-rack device..."