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Galanti to VPO Conversion

Building organ consoles for use with Hauptwerk, adding MIDI to existing consoles, obtaining parts, ...
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Galanti to VPO Conversion

PostTue Feb 05, 2019 1:49 pm

Recently a friend asked me to repair his Galanti Praeludium II. Even after cleaning up the usual battery damage and checking the power supplies, the CPU would not run. This also meant there was no Midi out. Checking the schematic, I noticed that all keyboards and pistons were arranged on 8x8 diode isolated matrices sharing a common data bus. This made it an excellent candidate for VPO conversion.

I had successfully done several pedal board conversions already using the Arduino Mega Microcontroller, but this was the first time I had attempted a complete organ. The Arduino has more than enough inputs so I hooked up the two manuals and pedal, the thumb and toe pistons as well as the two expression pedals. It now runs Jeux d'Orgues on an iPad using either headphones or the internal speakers and my friend is delighted with the result and claims it sounds better than the Galanti ever did. I'd like to offer some advice to anyone attempting something similar.

I stripped out all the electronics and power supplies except for the interface board in its cubby hole, just above the expression pedals. This meant that I was able to reuse almost all of the original cabling. The system started to exhibit strange behaviour (playing extra notes) as I connected more things to the common data bus and after much frustration I concluded this was the result of cross talk between wires in the many meters of ribbon cable. The solution was to cut the the data bus in halve leaving one half for the two manuals and the second half for the pedal and pistons, each half having separate inputs on the Arduino.

The expression pedals use LDRs and require modification to operate on 5 V so they can be read by the analog inputs on the Arduino. Basically I turned up the current on the LED for maximum brightness using the small trimmer pot. Then I wired the LDR in series with a 2.2 k resistor to +5V to create a voltage divider.

For amplification I used an external stereo amplifier. The organ speakers really benefit from a boost in the bass and treble which this makes possible.

Midi out is achieved with two 220 ohm resistors wired to +5 V and Tx (serial out) in the usual configuration.

The keyboard contacts consist of springs touching bus bars. They bounce badly and you'll need to incorporate an industrial strength debounce routine in your code. These bus bars are driven through a 3 to 8 line decoder which needs to be removed. You can then solder your eight lines to where the output pins were on the decoder or, more simply, directly to the bus bars.

All that, plus a few pages of C code, resulted in a successful conversion.
Visit this website (pages 2 and 3) to see a version of the code that uses an Arduino Mega and an Arduino Nano in tandem. There you can see how I handle scanning, MIDI merge, debounce, expression pedal encoding etc.


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