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[I am writing this when I am very tired. It will be terse.]

Now that the upper manual is basically controllable by MIDI, it’s time to look at the lower. The lower manual is more complicated than the upper. It has two sets of contacts for each key; one of which fires off the bass and chords, and one of which is ‘accompaniment’.

Essentially, then, the organ needs two sets of opto-isolators, one for each set of contacts. This means that each pin on the MIDI board needs to switch two LEDs; and for sanity’s sake, it’s probably a good idea to stick a tolerably heavy-duty diode (I have obtained industrial quanities of 1N4003s) along with the LED to make sure that current is only going where we think it is going.

First: looking at the ‘bass and chords’ contacts. These are in a scanmatrix arrangement; and so need a diode next to each key to avoid squirting current back up the scanmatrix pins on the mystery chip which seems to be running all this. (The diodes can be seen on the wiring for the lower keying; pps 8-9 in Part 2 of the TG-44 service manual, which I linked to previously.)

This means that, instead of our previous circuit, for each key, we have:

opto2

This is the basic outline for relayboard version 2b (2a is identical to 2 except that the two rows of chips can have different Vccs). This /should/ be interchangeable with v2 (so long as I’ve understood the organ correctly). In terms of board layout, it makes things a little denser; although the diodes on the MIDI side can sit right next to the resistors, the diodes on the other side will necessarily stretch things out a little. (I will post photos when the diodes arrive and I’ve had time to fiddle).

Each scanmatrix pin on the magical chip of doom deals with one octave, or twelve notes. It’s easiest then to match each octave to one row on a relayboard.

Plan for the ‘accompaniment’ keyswitches to come later.

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“no, no, make it stop, please at least use cable ties…”

There are now 20 notes active on the relayboard.  This is all the notes I can get working without going back and fixing some dud soldering.

What’s good about the relayboard design?

  • It works, and it works reliably. It is odd playing the keyboard and having the organ go off.
  • It is electrically very simple, and within even my questionable powers to assemble.
  • It is unlikely to explode without warning

What’s not so good?

  • It sounds like a room full of people knitting. Sound will follow.
  • It gets unseasonably warm. Not too warm, but more so than I am entirely happy with for something that performs such a simple job.
  • Corollary: it is probably drawing more current than I’d like.

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Playing with wire

The base of a national trophy makes a useful weight to hold down keys.
Yes, yes, it’s that trophy. 

According to the service manual for the Lowrey 44: “solo keying refers to the first seven upper keyboard notes which can only be played individually” (by which they mean, monophonically).  The rest of the keys on the keyboard are straightforwardly wired polyphonically.

Armed with the oscilloscope, I have managed to cause a bright blue spark and a bent bottom F key, but I have also managed to work out how the contacts on the back work, and managed to play a small tune on it with a bent bit of red wire.

Pink is not a creative colour.

The two contacts that are wired together seems to be the power.  The oscilloscope shows a constant deflection on these pins relative to ground.

The bottom seven keys are wired as pairs of contacts for reasons I haven’t entirely worked out yet.  Shorting the power to either of these contacts seems to cause the key to play.  The contacts are attached to the key they are behind – so they’re in the same order as the keys themselves.

The non-solo keys have one contact each – they are in groups of two, which will generally end up being one white note and one black note.  They too are connected in the order that the keys come.

Next step: work out where these wires actually go…

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If one removes the hardboard at the back of the Lowrey 44 and takes out the two screws at either end of the big metal tray (the one with the pedal board, the tone generator and the QC board on – visible at the top in this post), then that whole tray pivots outwards around its bottom edge and comes to lie flat.  This gives you access to the rest of the organ.

Pay no attention to the man behind the disconcerting metal flap…

The visible bits of the “rest of the organ” turn out to be: the backs of the keyboards, the disconcertingly gorgonoid backs of the tab stop assemblies, and two circuit boards on the back of the flap.  One of these circuit boards is labelled “C. F. B” and looks exactly like what the photographs in the service manual claims is the “Rhythm Board”.  The other board, on the other hand, is labelled “Rhythm Board” and looks like nothing on earth.

Something tells me these aren’t ROHS compliant.

Next challenges:

  • Trying to work out what contacts on the backs of the keyboards correspond to which keys, starting with the top keyboard.  I know that the top seven keys are wired separately (“solo”, according to the service manual) for some mystery reason.  I briefly attacked the things with an ohm-meter and failed to really get anywhere – so the next step is to attack once again the service manual and try to work out how the contacts line up with the schematics.
  • Trying to get the screws out of the pedalboard.  This is quite a major challenge given that the things seem to have cemented themselves in place.  I think I may need a bigger screwdriver.
  • Trying to work out how to lift out the whole keyboard/top assembly – it looks like I can, but the multitude of screws are disconcerting.
  • Getting a set of two manuals from a Church organ half-way across the UK on a train.  This could be fun…

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“I was a good cable in school!”

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Cables, cables, everywhere, nor any drop to – erm –

Things I have learned while attempting to record the Lowrey Genie 44 :-

  1. Do not attempt to record out of the headphone socket.  You will regret it; the sudden alternation of unexpectedly loud 50Hz mains fart and high-pitched tinnitus-inducing heaven-knows-what will not aid you in achieving the zen-like state required.
  2. Do attempt to use the phono socket on the back.  It’s very well hidden, though, being behind (but not central in) a small round unlabelled hole in the hardboard back.  On the Quality Control board, for those of you trying to correlate it at home.  Even if you manage to find the socket, if you have only one or two sounds going, the result is very quiet and a bit noisy.
  3. Except for the pedals, which’ll knock your socks off.
  4. That’s pretty much the best you’re getting in terms of output!

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Innards

Took the back off the organ for the first time and had a look inside.

Life in a box is better than no life at all.

Firstly, the innards mostly seem to be of solid wood too, or metal.  This is a good thing, because it means it’ll be easier to mount stuff when I need to.

There are three circuit boards mounted at the top of the organ – from left to right, these are the Quality Control board, which seems to be for tuning and general purpose fiddling, the Tone Generator board which is pretty self-explanatory, and the Percussion and Pedals board, which is likewise.

Access to the key switches is via solder points on the backs of the keyboards – I could see this by peering behind the three main circuit boards with a torch, but was unable to take photographs.

To penetrate any deeper into the organ will require unmounting the PCBs, which I’m not willing to do until I’ve sampled the organ.  So that’s the next step.

Oh, and also, the swell pedal is directly attached to the top of the power supply, for reasons which entirely escape me.

Feet and 240V AC. A match made in heaven.

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