Posts Tagged ‘Baldwin Theatre Organ’

Lower Keyboard contacts and pedal switches

December 28, 2009

Lower Keyboard Switches

I lifted the upper manual to take a look at the lower manual.  One interesting thing is that the wires from the top row of the upper manual contacts connect to the top row of the lower manual, note for note.  When I looked at the schematic, I realized that because this was what triggered the rhythm circuits, the manuals were permanently coupled for that purpose.  No real problem–I plan to cut the wires leading from the upper manual at this point and route the wires to the inner case for attachment to the DIN units of the MIDI controller (more on this later).

The lower keyboard was slightly different, but still had an easy way to bypass the resister and diode circuits so that direct on/off switching was possible.  Again, the upper contact was a whisker wire on a silver bar.

Lower Keyboard Contact Circuitry

The alligator clips are connected to where there is a non-resistant on/off switching circuit.  This means that a simple jump wire bypassing the diode (located just above the red alligator clip) will let the switch work through the existing wiring.

Here is a shot of the lower keyboard wires coming into the case awaiting snipping and connection to the DINs.

Lower Keyboard Wiring Inside Case (Marked by blue tape)

Pedal Switches

I was nervous about the pedal switches, having heard horror stories that Baldwin pedal contacts involved some sort of black goo.  The schematic showed a circuit that included a resistor and biased diodes.  The theory was intriguing:  the pedal 8′ and 16′ signals were always on but prevented by a diode from proceeding to the various filters and amplifiers.  When the pedal was depressed, the switch applied an 11 volt load to the diode, essentially opening it up to allow the signal through.  Very ingenious and somewhat Rube Goldbergish (look him up if you haven’t heard of him!).  I think it was a way to allow the signal to come on a bit gradually instead of abruptly.

In any event, I don’t need such complexity.  I was hoping that I could find an easy way to bypass the existing circuitry to get a simple on/off switch for each pedal note. 

Here is the switching assembly with the cover on:

What I labelled “pedal switches” above are actually plastic jacks.  The are thin, somewhat brittle, and therefore fragile.  I took care when working on this assembly to not bump them against any other parts.

For reference, the jacks are pressed down by felted tabs on the end of the pedals:

Pedal Felt Tabs

Cover taken off:

After the cover came off, I got my first glimpse of how the switches work.  There is a whisker wire passing through each jack.  When the jack is depressed, the whisker wire contacts a rail. 

Contact Points

The alligator clips locate the non-resistant switch points.  It looks to be a simple matter of jumping past the resistor below the black clip so that the existing pedal wiring can be used.  The red clip is attached to an uninsulated wire that grounds the entire pedal switch assembly.

So, this initial reconnaisance tells me that, with a little work on each contact assembly, I can use the existing wires to send switching signals to the MIDI controller.

Tracking the upper key switch wires

December 25, 2009

The Baldwin Cinema II has numerous wire contacts per key.  When a key is pressed, it lifts a jack (much like a harpsichord jack), bending various wires and forcing them to touch contacts.

According to the service manual, the stop sounds are controlled by small gold wires being pushed against elastomer contacts, while the rhythm sounds are controlled by a wire touching a silver rail.  The reason for the difference is apparently that the stop sounds, controlled by shorting a field-effect transistor, are susceptible to a “pop” unless the contact is made with gradually decreasing resistance.  The rhythm sounds are not triggered in the same way and can rely upon a basic on/off contact.

The elastomer technology is intriguing, and I imagine that there is potential for using the arrangement to control velocity MIDI inputs much like piano controls operate.  This would be useful if I were building a piano, but I’m building an organ.  The simple on/off signalling is sufficient, and, as it turns out, much easier to connect.

I lifted up the lid and took a look at the upper keyboard:

Lid up

A closer view of the top of the upper keys on the treble end:

And here is an out of focus photo showing the contact wires, jacks, the silver rail and the elastomers:

After poking around with test probes, I found what I was looking for: a simple on/off contact when a key is depressed.  Most of the wires coming from the contact assembly had bias resistance–something I didn’t want to go to the MIDI controller I would be building.  But, providentially, the upper contact before the limiting diode (shown below) showed a direct connection when a key was pressed. 

 

The black lead above is connected to an uninsulated jump wire that connects to ground.  The entire metal key frame is grounded.  The red lead is connected to a diode lead.  If I connect to the other side of the diode, resistance is 3K ohms.

The wires from the diodes are color coded and arranged by octave.  They control the existing circuitry that allows sounds from the tone generators.  I would like to keep the wires because they are so orderly.  Each color represents a note.  For instance, C is black, and it is a fairly easy thing to keep track of each key’s wire.

The problem is that the diode presents resistance and a one-way current limit that I don’t want.  I’ve seen other organ MIDIfiers simply tear out all the wires and start over with new wiring, but I couldn’t bring myself to waste the beautiful color-coded arrangement. So my proposed solution is simply to solder a jump wire past each diode and use the existing key wires to connect to the MIDI hardware.

In the next post I’ll put up photos of the lower keyboard arrangement.

Intro

December 25, 2009

The organ is dying.  I purchased the used but well maintained Baldwin Cinema II organ, model #214DR, about a decade ago because I wanted something with a full, 32-note, pedalboard.  I saw it advertised by a widow in Seattle for a pretty low price (for that era).  Her husband had played it, but, after he had died, it was just collecting dust in the living room.

It was in good shape and sounded very nice.  I bought it and proceeded to load it into my truck single-handed.  I did have a dolly and a bunch of straps, but the thing was heavy.  It took me about an hour and a half to get it into the back of my truck.

Baldwin console

The organ as it is now

It gave me years of pleasure.  I’m not a great organist, but for a time years ago I was a performance major in organ and I learned more or less how to play.  I happily played Buxtehude, Bach, Franck, hymns, and my own works in the living room.  It wasn’t a real pipe organ, but it sounded fairly nice.

Until the tibia started cracking.  The tibia stops were the prettiest sounds on the instrument.  Without them it was just a giant oscillator.  I had a technician repair the problem and was again happy.

Until it happened again.  And yet again.  As time went on, other stops started failing.  Hissing and cracking emanated from the organ’s four speakers.  I tracked down worn out transistors, dried out electrolytic capacitors, and various other decaying electronics, but replacing these things was only a temporary fix.  The electronics, some 38 years old, are undergoing solid-state decay.  I am convinced that it is irreversible and replacing the circuit boards is not worth the money.

So I searched the web and learned that others are MIDIfying their old organs.  Essentially, this means to take an old analog console and turn it into a MIDI capable instrument for controlling a computer that has sampled pipe organ sounds on it.  The improvement is amazing, and it doesn’t necessarily cost a lot if you are willing to do the work. 

I hope to chronicle the journey here.  I have already purchased the parts I need.  Today I mapped out the keyboard wiring and am convinced that I can keep most of it.  The rest of the electronics will be ignored or removed.  I’m not sure yet.

Here are the keyboards and tabs.

The organ has 5 pedal stops, 8 Accompaniment stops, and 15 Solo stops.  Because it is a theatre organ, the top manual is called the Solo manual instead of the Swell, and the lower manual is the Accompaniment manual instead of the Great.  I cut my teeth on classical organs and probably will be calling them Swell and Great.

In addition to the stop tabs, there are some 24 other tabs for various effects, couplers, special sounds (harp, chime, etc.).  There are also a bunch of buttons for rhythm functions and odd-ball sounds like car horns.  I never use these.

Finally, in the middle under the upper manual there are 4 preset “pistons” and a cancel button.  These would play factory-preset stop combinations and were not able to be programed.  The buttons are arranged mechanically to allow only one button to be depressed at any one time.  Press another button, and the depressed button pops out.  These probably can easily be used to control piston functions on the computer.

My initial research tells me that the stop tabs can be used on some MIDI hardware to send signals to control organ stops in the software.  I’m hoping that this is the case.  I am beginning to understand that there are complexities involved, but we cross that bridge when we come to it.

Next post: tracking key switch wires.


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