Adding MIDI to the Busker Organ

by Michael Jeffs

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Adding MIDI to the Busker Organ
Having built the Busker organ, I decided that I would like to experiment with a MIDI version.

Rather than alter or change the air box and pipe arrangement, I have incorporated the MIDI interface and solenoids into the existing organ. The idea being that I can still play the rolls, or the MIDI files at will.

 


The modified tracker bar. The solenoid connecting socket on the LHS is airtight through into the air box


The underside of the solenoid carrier, with the plug for connecting to the socket


Top view of the solenoid carrier. The valves are leather pads on foam on the solenoid plungers. The travel on the solenoid is only 4mm, but this still seems to give enough area for the air flow when open, and seals when closed. The pcbs for solenoid connection are home-made etched copper pcb


Solenoid assembly in place


Paper roll in place. There is enough clearance between the roll and the solenoid assembly (just), so that both the roll or the MIDI can be played

The MIDI interface. The coloured wires (solenoid drive outputs) go with the air pipes underneath the air box to the socket.


The entry for MIDI DIN and 12 volt power socket

 

 
My tracker bar is about 4 mm taller than the original. I made the central part of the tracker bar out of one piece, which has cone-shaped holes to give as much air flow as possible.The solenoid valve holes go straight into this cone area, connected to the tracker bar plinth and air feed pipes.

The solenoids are 12 volt miniature suction type from China.

The MIDI interface is a kit from Orgautomatech with the Parametor program for testing.

A cheap MIDI to USB cable on the internet, which I am using with MIDI Player.

 

I found it desirable to try and reduce the solenoid metal-to-metal click noise. I limited the solenoid plunger movement by about .5 mm, so that the circlip/retaining washer hit the soft pad just before the solenoid fully-on position.

I experimented with various soft materials about 1 to 2 mm thick and made some slightly larger C-clip washers.  (I have not tried this but it might be easier to have an extra thin washer and keep the existing C-clip).  As the travel of the solenoid is only 5 mm, if you lose 1 mm on the valve close position and say 1 mm due to the limiting pad., the remaining 3 mm annular gap does seem to allow enough air.  Although the air pressure in the box does help keep the valve closed, some slight spring pressure is still required.

There is still noise but a thud instead of the metal to metal 'click', practically inaudible when music is playing. (I retained the valve pads to the plungers with small magnets held in retaining collars soldered to the valve pad plates. The magnets also enhance the pull force, if the magnet N/S poles and the + - voltage of the solenoid coils agree).

The solenoids are not ideal, and need more travel and a bit more oomph, but they are small and appear to work, and they were cheap!

 

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