Here is a diagram of how I hooked the triggers up to the voice board. This is a follow-up post to answer some questions about this previous post.
There is a board with 3 transformers on it. That's the voice board, the other board with many diodes is the rhythm board. On the voice board there is an edge connector with many multicolored wires leading to a bunch of switches, which lead to the rhythm board. There should also be a ground connection to the voice board (mine was black) and a negative supply wire (mine was thin and green).
There are nine separate sounds on the voice board and the multicolored wires trigger each sound when they receive a negative pulse. I built simple trigger inverters for each of the nine lines. I used a simple op-amp voltage inverter with a +/-15 volt supply from the rest of my synth. Be sure to connect the ground of each supply together. I'm still not sure of the best point on the voice board to use as a ground.
As far as the hum goes, mine has a similar problem. You could check for loose grounds on the outputs. I replaced the main power filter capacitor, which is located on it's own board. This helps, but the hum is still there, just at a lower level. There are many grounds on the system and I believe they are star grounded to the ground on the output jacks.
Also, I just want to warn you that there is mains supply running through the wire bundles. There is a thicker pink or yellow wire which carries mains supply to the volume power switch and neon bulb on the front panel. Just something to watch out for when you have it open.
