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Sanity check


Cruft of ages, unglued for me…

I have sanity-checked yesterday’s results!

The non-solo keys need to be wired to point BB, which I tracked down on the circuit diagram.  This turns out to be accurate on the rhythm/percussion board – and the wire is, indeed, pink.  Going from the left of the board there are two groups of two big orange capacitros.  To the left of the second group of two capacitors are three spiky contact things.  The uppermost of these has the pink wire and is point BB.

To test this, I rigged up a trailing wire between this contact and the note contacts (also identified from the PCB diagrams) and checked that everything worked.  It did.

Above the first group of two capacitors is another set of three contacts.  Point BA is the middle one of these: according to the service manual, the first one is the sustain control line, and the third one is at ground.  It has a turquoise wire attached to it at the moment.  This, jumpered to the seven solo contacts, gives the required results.  So this is where the second half of the relayboard needs to be jumpered to.

Other stuff:

  • Have successfully de-glued the plastic plugs and sockets that connect the pedals and the amplifier to the top of the organ.
  • Have utterly failed to undo any of the structural screws.
  • In other news: I need a bigger screwdriver.

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.

Conclusions:

  • 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.

Next steps:

  • 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…

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…

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…

 

“I was a good cable in school!”

Sampling the thing

 

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!

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.