Acquired a Praeludium II that needs work - questions

[mwdiers]

I acquired a Galanti Praeludium II for $500 that was part of an estate for someone who passed away. I jumped at the opportunity, as this is the model organ that I learned on years ago, so I know it well.

It has 9 pedals not sounding, one key sounding inconsistently, some noise coming from the left mid-range speaker, and 4 non-speaking stops.

This unit was built in '88 and has the latter pedalboard with the "rubber hose" segments and the dome membrane switches.

8 of the 9 pedals are not working due to a clipped wire behind the 15 pin connector. Judging from the mouse droppings I had to clean out, I think it was bitten through. That's an easy fix. The 9th pedal is not sounding consistently, but that seems to just be weak rubber which I plan to reinforce with some felt. The switch works fine when I manually actuate it.

I'm sure I can solve the key on the Great that's firing inconsistently, but it will be a pain to pull out the manuals to examine the switch mechanism.

I'll worry about the speaker noise later.

But it's the non-sounding stops that I'm most concerned about.

The stops are all on the Great: Flute 4', Fifteenth 2', Mixture III, and Chimes. The stops light up. I notice faint white noise that plays when those stops are activated, except for Chimes.

Voice board 2, I noticed is missing four chips. See here for a picture. I'm guessing this is normal, but I don't know for sure. (If they are indeed not supposed to be there, then I can only assume that the mixture ranks must be sampled individually and mixed, which brings the rank count to 39. With 4 voices per chip, one would expect 2 blank voice chip sockets with the remaining 10 filled — which is what I see. This is all just guesswork on my part.)

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I already removed the NiCad battery which had leaked onto the CPU board. Thankfully it didn't do any serious damage. Just some surface corrosion on a couple leads and some bubbling of the board varnish. All other organ functions seem to work other than those noted above, although I didn't test MIDI yet. I also didn't try changing temperaments, because I don't have a manual, and I forgot how.

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Interesting observation: In the model we had at my church growing up, Galanti replaced the spring reverb with a Nanoverb a month after they installed it. The salesman was a friend of ours, and he wanted to make sure we had the digital reverb. They velcroed it to the chasis where the spring reverb used to be.

However, this unit has neither a spring reverb nor a Nanoverb. At least it does not have a boxed Nanoverb. The reverb unit is an exposed board sitting behind the card cage. One of the chips says "Gem.OEM" and "Alesis".

[michaelhoddy]

Regarding your 4 missing voices, it sounds like you indeed have a single voice path on one of the voice boards (EPROM, M114, DAC, output circuitry) that has an issue. It has been years- decades- since I worked on a Praeludium II, so one of the more knowledgeable folks (Arie, JBird) hopefully can point you in a more specific direction.

Regarding the reverb, only the very earliest 1987-vintage Praeludium II's had the spring reverb. Right around 1988, they replaced it with an Alesis-sourced board which was a big (for the time) improvement. That board is present in all later Praeludium I's and II's, and all Praeludium III's. That's what you have.

[jbird604]

You need to find the schematic somewhere. Not sure where you would start looking. Artie Specht used to be the go-to guy on Praeludium II stuff, but I think he has disappeared entirely from the scene. But having the schematic you can could carefully trace the paths of the four missing stops and check each step of the way with a signal injector/detector to see where the audio is getting lost.

I seem to recall that the voices come off the M114 chips through tailoring resistors to balance the levels, then get mixed down into fewer and fewer channels until you wind up with the two basic audio channels on the audio processor board in the cage rack. Your trouble could be with the resistor or op-amp or whatever handles the audio as it comes out of the M114, or could be anywhere in the mixing circuitry. Could even be a defective M114, I suppose. You have a lot of those, so you can swap them around for troubleshooting purposes. But before you do that, you need the schematics. Otherwise you're flying blind.

[mwdiers]

Well, crap. I found this post from Arie from a few years ago:

Hi,

For your reference,

The Great Princ. 8 and Octave 4 come from tone board #1 - they share resources IC4 is the voice eprom, IC9 is the music processor chip.

The Mixture III, comes from tone board #2 - sharing with the Chimes stop IC 3 and IC8.

The Chimes stop is divided in 2 parts. The other half of the Chimes is shared with the Gt. Flute 4 also located on board #2, on ICs 2 and 6.

There is also a CPU IC on each tone card that could be the issue.

But since there are problems on more than one board, my guess is a data line problem, or a data corruption issue, likely to do with the main CPU board.

AV

This can only mean that those missing chips are indeed the culprit. Flute 4' EPROM is supposed to be in IC 2, which is missing. Mixture III is supposed to be on IC 3 and 8, both of which are missing.

I'm sure I can get the missing M114S chips, but where in the world would I get the EPROMS for IC2 and IC3?

[arie v]

Hi,

missing stops, these are supposed to be generated on board 2, code number 76.643.
This board, from the picture is missing 2 M114 ICs, along with their EPROMS. The Eprom codes are 10824 and 10825. These ICs, if missing explains why 4 stops are missing.

Pedalboard issue, with intermittant note, more likely than not, is a wonky switch. Would need to know which pedals are not sounding. I can probably sort it out for you.

As for keyboard issues, intermittant notes was a common problem. You can try to cleam it, but better yet just replace the coil contact spring.

Hopefully I have been of some help here.

AV

[mwdiers]

Arie,

This is very helpful.

I acquired a PDF scan of the service manual from a helpful individual in the UK. According to the diagram, IC3, in the US, should be EPROM 10833. 10825 is for the Italy and France. In Germany and Great Britain: 10829. I don't imagine it will matter which of the three I am able to get, except that the samples will obviously be from other organs. Looks like only IC3 on board 2 has alternate voicing by country.

I emailed General Music asking about those chips. Is there any other place where I might find them?

I am assuming that the M114 chips are actually DACs manufactured by STMicroelectronics. Not having much luck searching for them, but perhaps there is a compatible replacement part.

As to those coil contact springs, where would I acquire replacements? I'd probably want to buy several so I have spares.

As to the pedal, this board uses the rubber tube + rubber dome switches. The switch itself seems to be fine. If I manually actuate it, it sounds every time, so I think it's just a weak rubber hose, which I can just reinforce with some felt to stiffen it up a bit.

I also need a few felt pads for the pedals. A bunch of them had skidded sideways, so I was able to reposition them, but a few lost their adhesive.

[mwdiers]

The pedal board is fixed. After soldering the clipped wire behind the 15-pin connector, the 8 pedals on the left started working. There were three pedals that were firing intermittently. I rolled up some felt and sprayed some craft adhesive on the felt, pushed it into the rubber tubes on those three pedals. I reinstalled the loose up-stop pads with contact cement, and replaced the missing felt on a couple of them with those felt pads you can get for for the bottom of furniture on wood floors. Working perfectly.

The intermittent key (D above middle C on the Great) was simple to fix. I just cleaned the bar and spring with QD Contact Cleaner and a paper towel.

Now if I'm lucky enough that General Music can provide me with the missing EPROMS and DACs, I'll have a fully working instrument. That might be a stretch after 30 years. Perhaps they can burn new EPROMs if they don't have spares left over.

Anyway, worst case I have a decent Hauptwerk console, which was my main goal in the first place. A pity the swell expression pedal doesn't send CC, though.

[don60]

I can probably hook you up with someone who has the EPROMs. PM me if you are interested.

[arie v]

Hi,

a couple of things,

1) General Music, in the US, is no longer active. I would be surprised if you get a reply by e-mail, or someone answering the phone. The Chicago address no longer exists.

2) I you have a Praeludium II, you need schematics for for the PII. GeneralMusic also made an organ called a Plenum. Do not use the Plenum schematics when it comes to E-proms, stop configurations, as the organs were different.

3) the M-114 IC, is more than just a DAC. It should be more correctly called a digital signal generator. It was quite a piece of technology when it came out in 1986. Many companies used this IC. I believe that these IC's are available from companies that used them or from service techs.

AV

[mwdiers]

Hi Arie,

Yes, I have the correct schematics for the original PII. So I'm good there.

I found a gentleman in Virginia who is able to burn fresh copies of any of the Praeludium EPROMs for $20 ea. + shipping. I have them on the way.

I found an online chip shop in Italy that had the M114s, so those are on the way as well.

I have since discovered a couple more issues with the mixer / amp:

1) The right channel is weak and a bit distorted. This is true whether I am using the internal amp, or using the rear outs, and it is true for the audio from all divisions. This leads me to believe the problem must be on the mixer board itself. I'm guessing I should first check for weak solder joints on the components that are shared by the right channel for both the rear outs and the internal amp. There's only 7 of them.

2) I am also having issues with the rear outs and the internal amp. At first, I could not get the rear outs to work at all, which is bizarre in itself. After disconnecting and reconnecting the Pwr Amp Input connector and removing and reinserting the 1/4" plugs from the rear outs a few times, the rear outs started working. But now I can ONLY get audio from the rear outs. The internal amp is getting nothing.

The most likely culprit here seems to be the muting relay on the amp board, because from my read of the schematics, the rear outs and the internal amp should both be getting a signal, or neither should. The two muting relays are in parallel, and should default to ground until the CPU is up, and then both should pass audio.

Anything else I should check on either of these issues?

https://f001.backblazeb2.com/file/mw...P2%20Mixer.png
https://f001.backblazeb2.com/file/mwdiers-sharing/Galanti/P2%20Amp.png
https://f001.backblazeb2.com/file/mwdiers-sharing/Galanti/P2%20Auxiliary%20Boards.png

[Innocentti]

The internal speakers are muted by the phones jack - see cross over input.

[mwdiers]

Yes, but I did not plug anything into the phones jack since acquiring the instrument, and the internal speakers stopped working while I was mucking around trying to get the rear outs to work. I will check the phones jack, but I highly doubt that's the problem.

[mwdiers]

So, you were right regarding the headphone jack. The jack is bad, and moving the instrument around in my work area must have been just jarring enough to make it cut audio to the mains. I bypassed the jack entirely, and now have fully working mains (except for some nasty speaker rattle).

Left and Right channels are both good on the mains, but, oddly enough, not on the rears. There one channel is very weak. This should be an easy problem to troubleshoot, since if the mains are fine, the problem must be in the connections to the mixer, or (another) bad jack.

[mwdiers]

Getting closer on this. The M114S chips arrived. I am still waiting on the freshly-burned EPROMs. Hopefully sometime next week.

The rattle issue on the built-in speakers was because the woofers are shot. The foam had completely disintegrated. When I disconnected them, I had no rattle or distortion whatsoever. They did not look worth repairing, so I ordered replacements from simplyspeakers.com: https://www.simplyspeakers.com/repla...er-w-1034.html They should be a drop-in replacement.

Had fun figuring out the amp power and calculated the crossover. The amp is 70W per channel.

The crossovers are a weird design. Probably trying to save money. It's first order on the high-pass, but second order on the lowpass. The lowpass coil's impedance is also lower then it would normally be, evidently in an attempt to reduce the dip at the crossover point, but in the process that introduces resonance. The summed response has a 1.5dB hump at 150Hz, and a 2.5dB dip at 350Hz. https://f001.backblazeb2.com/file/mw...0Crossover.png

Perhaps there's some EQ going on in the amp circuit to compensate, but I doubt it.

[jbird604]

I'm confident there isn't any EQ to compensate for the odd crossover design. The internal speakers in many organs don't have "textbook" crossover configurations. Personally, I haven't found that it made any audible difference to replace the old foam-surround 4 or 6 ohm woofers with good quality textile-surround 8 ohm woofers. I know some folks will shudder at the thought, and yes, the foam theoretically extended the low frequency response, and the different impedance will alter the crossover point and the sensitivity, but in practice I haven't heard any important difference.

The crossover design is so loosey-goosey anyway, there are already some dips and peaks and odd resonances. Trading one set of oddities for another seems to be ok. Anyway, the internal speakers are probably going to be greatly overshadowed by the external speakers in nearly any setup, so I don't worry much about them.

[John Vanderlee]

On the other hand, with some elbow grease and a few bucks, the speaker could have been rebuilt with a DIY kit.

[Coenraads]

When a friend asked me to take a look at his Galanti Praeludium II, I checked the power supplies and repaired the usual battery mess, but still the CPU did not run. I pronounced it dump fodder and suggested that we salvage the pedal board and that he acquire two MIDI keyboards so I could put together a VPO for him, something I had already done successfully several times. By this time, I had studied the schematic in detail and noticed that the Galanti was matrix wired all the way. It struck me that this made it an excellent choice for conversion to a VPO.
I stripped out everything except for the ribbon cables and the interface board in it's cubby hole above the swell pedals. The only problem I ran into was crosstalk on the many feet of data line ribbon cable. I solved this by splitting the cable in half, and connecting the keyboards to an Arduino Mega while assigning the pedals and Pistons to an Arduino Uno. In retrospect, a single $20 Arduino Mega could have handled the whole thing but I wasn't about to rewire everything.
The nice thing was that I was able to salvage the functionality of the thumb and toe pistons as well as the two expression pedals. I didn't bother with the stop rail since I suggested using the Jeux d'Orgues app on his iPad as his instrument. Stop control is therefore done via the iPad's touch screen.
I hooked up an external stereo amplifier and connected it to the built in speakers.

I recently got a very nice email from my friend telling me how much he enjoyed playing his "new" instrument and that it sounded better than the Galanti ever did.
The story is posted on the Hauptwerk Forum:

http://forum.hauptwerk.com/viewtopic.php?f=15&t=17343

The C code for the Arduinos can be found on my website:

https://sites.google.com/site/casavantopus400/

So, consider this an option.
John

[mwdiers]

I'm confident there isn't any EQ to compensate for the odd crossover design. The internal speakers in many organs don't have "textbook" crossover configurations. Personally, I haven't found that it made any audible difference to replace the old foam-surround 4 or 6 ohm woofers with good quality textile-surround 8 ohm woofers. I know some folks will shudder at the thought, and yes, the foam theoretically extended the low frequency response, and the different impedance will alter the crossover point and the sensitivity, but in practice I haven't heard any important difference.

The crossover design is so loosey-goosey anyway, there are already some dips and peaks and odd resonances. Trading one set of oddities for another seems to be ok. Anyway, the internal speakers are probably going to be greatly overshadowed by the external speakers in nearly any setup, so I don't worry much about them.

Well, I made an incorrect assumption that the full-range speakers would also be 4 ohm. They aren't. They are 8 ohm. This makes a bit more sense now, as the high pass is now close to 200, just like the low pass. The resulting resonse: https://f001.backblazeb2.com/file/mw...0Corrected.png The hump is now more pronounced, bug the dip is probably not audible at ~ 1dB.

In my case, this organ will be in my 12x12 study. Not much room to work with. I have a pair of studio monitors I use with Hauptwerk, but I still want to be able to play the P2 itself, especially for convenience sake.

I discovered the source of the hum. It's coming from the Reverb unit. If i turn off the reverb, it all but disappears. Perhaps a grounding issue on the reverb. Old Nanoverb units are cheap. I might just grab one, and use that instead of the OEM one. Just need to convert the molex plug to L/R phono plugs.

[mwdiers]

John,

Great info. I will certainly keep that in mind. I've never done Arduino work, so thank you for making the source code available.

I had originally intended to do a more thorough MIDI conversion on the P2 and only use it for Hauptwerk. But I when I found how much of the instrument was still functioning just fine, I pivoted into restoring it. I still would like to get the Swell Expression working with MIDI, though. It's too bad that Galanti didn't bother to midify anything but the manuals and pedals. I have heard some people say this was because MIDI was in its early stages. Hogwash. My Yamaha DX7, the first widely-available MIDI instrument of all, is fully controllable (and programmable) via MIDI, and that predates the P2 by 10 years.

I'll admit that I have a lot of nostalgic attachment to the P2, since it was the instrument of my youth. I'm actually surprised how much is working. After working through the bugs, and presuming the now-dead stops work after installing the EPROMs and M114's, the only remaining electronic issue is the reverb hum.

I was not aware of Markus Sigg's iPad apps. Those look great. I am familiar with the Burea from Hauptwerk.

I intend to go the Mac Mini route for this instrument by the time I am done. I have a lot invested in Hauptwerk organs. The new Mac Minis have all the horsepower and memory (32Gb) I would need. Just need a couple touch screens for it.

I use the Mt. Carmel Skinner (and a couple others) to record the hymns for my church, many of which are available here: http://wittenberglutheran.org/hymns/ I am really looking forward to playing the Skinner from the P2.