This post does not contain any pretty photos. Those in search of organ erotica will need to come back next time.
In the grand scheme to decouple the manuals of the Lowrey Genie 44 from the back end, I need to build something to sit, electrically, where the keyboards “were”, to emulate the keyboards. I’ve decided to use relays for this purpose, given that I don’t entirely trust the electrical environment inside the organ, and I’d rather not spend ages soldering transistors down just to generate that lovely burning semiconductor smell that we all know so well the first time I turn the thing on.
Each key on the top keyboard is effectively a switch; and as such I’ve obtained a moderate sized bag of single pole single throw relays from RS which claim to be able to take up to 30VDC through the switch bit, and have a 12V coil voltage.
This is quite convenient, given that the MIDI Boutique decoder I’ve got my eye on works on 12VDC – so I can avoid proliferation of power wiring.
How should the relay boards work?
Now that I have the correct service manual (the TG44-I Service Manual from the Lowrey Forum website – you’ll need both PDFs) for the organ, I’m closer to an answer, at least for the upper keyboards.
The upper keyboard is divided, as I said before, into two groups of keys. The upper 37 form the “upper keyswitches”. There is a common bus that runs along these, which is connected to the terminal for each key switch. That’s a horrible sentence – this diagram may help.
For the 37 “upper keyswitches”, the bus line comes out of the murk of the Auto Wow circuitry (this is at the top left of schematic 2 in the service manual, on page 14 of part 1). This is labelled as point “BB”.
Finding point BB involved a significant treasure hunt; I’ll save you the effort if you’re following along at home and point out that point BB is at the top left of page 5 of part 2 of the service manual, on the PCB layout for the Pedal and Percussion Board. This should be the terminal where the disconcertingly pink feed cable I found last post should emerge.
Where do the other ends of these wires go? The answer to this one can be found on page 2 of part 2 of the service manual. The contacts are scattered around the Tone Generator and Keying Board in what seems to be a fairly ad-hoc order in some places.
So, the first part of the relayboard arrangement for the upper manual needs to sit between the pedal/percussion board and the tone generator board.
The remaining 7 keys on the upper keyboard, the lowest 7, are the “solo keys”. These are monophonic; only one can be played at once. It turns out that my previous supposition that they shared a bus with the non-monophonic keys was – to put it bluntly – wrong. Page 18 of part 1 of the service manual clearly shows that the bus for these keys emerges from point BA:
Turning once again to part 2 of the service manual to consult the PCB layouts, point BA turns out to be in the upper right of page 4 – that is to say, right next to point BB on the pedal/rhythm board.
Where are the other ends of these? There is less distance to look this time – in fact, the keyswitch contacts for the seven solo keys are on the left hand side of the very same page 4.
This means that these 7 need their own isolated area of a relayboard, and are strung between one side and the other of the pedal/percussion board.
The lower manual is a thornier area that, as yet, I will not touch.
- Upper manual relayboard needs to be in two parts.
- One takes its bus from point BA in the middle of the rhythm/percussion board and jumpers it to individual keyswitch contacts on the tone generator board.
- The other takes its bus from point BB in the middle of the rhythm/percussion board and jumpers it to individual solo keyswitch contacts on the side of the rhythm/percussion board.
- Attach a piece of wire to BA on the rhythm/percussion board and see if I can play the keyswitch contacts for the non-solo keys.
- Attach a piece of wire to BB on the rhythm/percussion board and see if I can play the keyswitch contacts for the solo keys.
- Try to work out how to attach wires to the things…