The Organ Donor Project- the Dissection

(Note- This is an intro and a description of the disassembly of the organ. See The Recyclone Rotary Amp and The Blacklord Synth for projects using these parts.)

When Gordy, my friend/gear scout/hoarding enabler, called and asked me if I wanted an old Hammond organ I jumped on it. Gordy is one of the coolest people I know. The fact that my wife likes him in spite of the fact that he brings me a constant supply of broken junk is evidence of just how awesome he is. When he dropped it off and we man-handled the beast into the house I gave it a quick once-over. It was a mid-70's 'granny organ' with two keyboards, bass pedals, a rhythm section and a Leslie rotary speaker. Next I plugged it in to hear what I had. The first thing I heard was the crackle of bad connections and the whirr of the unlubricated Leslie speaker. The keys worked well and the organ sounds were adequate, but nothing special. This wasn't a classic Hammond tone wheel organ, it was one of their early solid state instruments, lacking both the versatility and fidelity of a modern keyboard and the indescribable warmth of a classic. Finally, I tried the rhythm unit and I was floored! It had 16 preset beats with four variations each, for a total of 64 different beats. They could be played individually or the four variations could be played in succession with a rudimentary sequencer. The drum sounds themselves fell somewhere between a classic Maestro Rhythm King and a Roland TR-77- very analog and absolutely beautiful! OK, now it had my attention.

Aside from the Hammond logo and an 'Animation by Leslie' badge there was no obvious model designation. After a Google search for the serial number I figured out that I had a Hammond Aurora 8200 with an Auto-Vari 64 analog rhythm section. A quick check for the general value confirmed my suspicions- a typical <$50 thrift store score. Next I did a search for the Auto-Vari 64 and things got weird. This drum machine came in two versions- a built-in unit and a free-standing accessory unit. A quick hit on eBay showed the accessory version going from $250 and up. Further digging revealed that the built-in unit that I had actually had more features. It had inputs to trigger the bass drum and snare sounds from the keyboards, a trigger output for an arpeggiator and a syncronized start input. This was an immensely hackable analog drum machine just waiting for me to make it awesome.

What do you do when you have an awesome sounding drum machine in a crappy sounding organ? If it was a better quality instrument it would be worth restoring, but this is a major chore. The entire organ needs to be disassembled, cleaned and put back together. Each step needs to be documented and the parts need to be kept organized. It's not a task to be taken lightly- it's a lot more work than you think and many people give up. This organ wasn't worth the time it would take to make it sound clean. In this case the only option is to remove the drum machine and install it in a custom cabinet.

So now I was stuck with a mediocre sounding organ without a cool sounding drum machine. It was useless and in the way, but before I could haul it off I was going to strip it of useful parts. It had a Leslie rotary speaker, an amp, speakers, bass pedals, a volume pedal, two keyboards, plenty of cool switches, a reverb spring tank and a bunch of circuit boards with tons of awesome old-school components. Aside from the drum machine, I could also build a rotary speaker amp cabinet, a spring reverb, a lofi square wave FM bass pedal board and who knows what else.

Why start from scratch when there's an internet full of projects to learn from and ideas to borrow? I figured someone else must have done some of these things already so I hit Instructables and searched for 'Auto-Vari' but there was nothing. Hmm... I tried 'recycled organ', 'organ Leslie', rotary speaker' and 'bass pedals' and found nothing. I knew what I had to do.

This Instructable will document the dis-assembly of my organ and highlight the useful parts and components. I will also link to any subsequent projects using these parts and sub-assemblies. While this will focus on the Hammond Aurora 8200, many of the parts and techniques are applicable to a variety of makes and models.

Use common sense. Make sure the organ is unplugged before opening or disassembling it. Wear gloves when handling sharp things, safety glasses when working with shattery things and a respirator when working with fumey things. You only have one body and you will get extra points at the end if you keep it in one piece and in working order. Proceed at your own risk- don't blame me if you try to disassemble an organ and it maims or kills you. Organs can be ornery. Absolutely no part of the electric organ is edible, ever, no matter how many 'R's in the month. (The pipe organ is edible, however, and is quite delicious, which led to its near extinction and forced the last remaining members of the species to seek protection in churches.)

The Auto-Vari 64 drum machine that is built into the Aurora 2800 is pretty easy to remove but care must be taken to get as much information about the unit as possible. Since it's powered from the organ's main power transformer, I'll have to determine the operating voltage to make it work on it's own. There are also a lot of wires that I'll have to trace to figure out what they do.

Gently prying the top cover of the organ gave me access to the organ's guts, being careful to engage the safety catch on the lid bracket to prevent injury or damage to the fragile circuit boards. Removing two screws near the top of the drum machine bracket allowed it to fold down revealing the Auto-Vari 64. Removing a few screws freed the drum machine. I disconnectet the 15 pin block connector from the back of the unit.

By carefully probing the block connector's pins with a multimeter while the organ was turned on I found the voltage in pin. Once I determined the operating voltage I turned the organ off and unplugged it. Now I traced the wires from the block connector to determine their functions. The wiring harnesses are a technicolor spaghetti that looks very daunting. I just started from the connector and followed the wire, carefully snipping any cable ties or retainer clips. The wires will eventually connect to circuit boards, busses or sub-assemblies. The circuit boards have labeled connectors. The busses are common connections for voltage or ground connections. There are also wires that connect to sub-assemblies like the volume pedal or accompaniment section. I labeled each wire and snipped it from the harness leaving enough wire to connect to other components later. The block connector has 14 pins with attached wires. When it was all labeled and cut free I put it aside for later.

I searched online for a service manual for the drum machine and got lucky. This shed a little more light on the function of the individual connections. There were some interesting possibilities. The accessory version has a single audio output, but the built in unit has a high and low output. This may allow me to send the lower pitched and higher pitched sounds to separate amps or effects processors. It also has triggers to control the snare and bass drum sounds from the foot pedals and bottom keyboard. This means that I may be able to control the sounds with an external sequencer or trigger. There's also a synchronized start trigger so the drum beat starts when the keyboard is pressed. There is also a trigger signal that controls the arpeggiator timing. This could be used to gate an external signal or trigger an external drum unit or sampler. All of these external controls pass through the block connector.

This drum machine has a ton of potential for modding. I'll cover that project as a separate Instructable later. I'll link to it from this project so keep your eyes open.

With the Auto-Vari 64 removed I started from the top down stripping the organ. The voice select panel with all the multicolored toggle switches was attached to the drum machine bracket and held in place with four screws. I carefully cut the wires from the tangle, leaving enough wire on the switches to work with later. These are really cool switches but they are built into the panel and cannot be removed and used separately.

I returned the drum machine bracket to the upright position and put the screws back in to hold it up. Next I started removing the individual circuit boards. I worked from left to right and removed the wiring harness as I went. Hammond designs their organs with discrete boards for each function within the design. This makes a lot of sense as the same vibrato effect or passive mixer board can be plugged into many different models. This makes disassembly easier and offers intriguing possibilities for later hacking.

Next I removed the trim pieces from the keyboard and removed the drawbar assembly. These are basically sliding pots mounted in a row to mimic the form factor of traditional organ drawbars. With the trim and drawbars removed I took out the keyboard release screws from the underside of the organ desk. This allowed the keyboards to swing up to give access to the circuitry underneath. I removed the wooden trim pieces from the aluminum keyboard frames. I removed the keyboards by removing the screws connecting the hinge the the main organ body. I carefully traced the keyboard wiring harness back to where it plugged into the main voice board and unplugged it from there.

While I was removing the keyboards I noticed something interesting. One of the trim pieces had a gold colored strip and a toggle switch labeled 'arpeggiator'. When the organ was still working I had flipped the switch but noticed no effect on the sound from the keyboards. I figured it was a loose connection and thought nothing more of it. When I was removing the panel with the gold trim piece I was surprised to see a large stalk of wires connected to the back like a massive nerve ganglia. Closer inspection revealed that they were all connected to the gold strip and wired into the main voice board in correlation with the keys on the bottom keyboard. I assume the gold strip was similar to the touch strip on the Suzuki Omnichord, allowing the player to 'strum' the instrument. I'm curious what this sounded like now. That will teach me to RTFM! (Or at least GoogleTFM)

With the keyboards removed I finished stripping the boards and wiring harness. I put the boards aside for later processing, pushed the remaining harness through to the back side of the organ and went to get a band aid for my bashed knuckle.

Now for the back of the organ. The first thing you'll notice is the big green block of foam. That's the Leslie rotary speaker. I removed that and followed the wiring harness back to a six pin block connector. This is an awesome piece of kit! It uses two 120v motors to rotate a foam cone that directs the output from the speaker in a spacey circular pattern. It's a really cool old effect from the pre-digital days.

With the Leslie out of the way I had more room to get to the other goodies on that side of the organ. First I removed the spring reverb tank. This gives a reverberant, echo-y effect by sending the audio signal into a transducer. The transducer is basically a tiny speaker that causes the sound to travel through a few long springs. The sound signal literally bounces back and forth along the spring causing echos which are picked up by another transducer at the other end, this time acting as a microphone. This signal is then mixed back with the original 'dry' signal to give varying degrees of reverb. When I removed the reverb tank I saw something I've never seen before- the driver for the tank was mounted right to the side of the unit! Hammond's modular design esthetic has won the day again. Usually the signal for the reverb tank comes from a sub-section of a larger board within the device, making it much harder to reuse. To make matters worse, the transducers used require odd impedances which means they can't just be driven by a line level signal. Having the driver board mounted on the unit means that it just needs voltage, signal in and out and a few pots and switches to become a functioning reverb unit.

Hidden back behind the reverb tank is the pedal board. This is a separate assembly with thirteen pedals and a block connector. It works similar to the upper keyboards with a common voltage in and ground and individual leads for eack 'key'. It also has a trigger for the drum machine that detects any pedal being pushed. The pedal board assembly was held in with two screws on each side and slid out from the back.

On the other side of the organ is the amp, power supply, speakers and volume pedal. I cut the pasteboard cover from the volume pedal and removed the four screws. This is a foot pedal with a switch and a pot built in. I removed the two amps from their mount on top of the power supply and then removed the power supply itself. Finally I removed the speakers and the rest of the wiring harness.

Whew.

We're not done yet. Now I went over the whole organ and removed the hardware including the board retainer clips, socket holders, hinges, brackets, spacers, screws and other bits. This is all stuff that costs money. More importantly, you never know when you'll need a lid brace, hinge set or 'just the right bracket' to finish a project. Every workbench needs a big jar or two full of screws.

I also removed the grille cloth from the front of the organ. I'll probably use this to cover the stand-alone Leslie amp I'm thinking of building with the parts from this organ. You'd be surprised how much a speaker shop wants for this stuff.

By now I have a huge pile of 'junk'. What will I do with it all? I'll cover that in the next step.

After turning a functional organ into a pile of scrap parts and making a mess of the living room will something productive actually come from it? Am I just some crazy guy that likes to disassemble stuff and sort the parts? Is my wife the most patient person in the world for putting up with all this? Yes to all of it.

Let's take a look at what we got. First of all the Auto-Vari 64 is the big prize. This is an anaolog drum machine with lots of fun features and lots of hacking and modding potential. Hammond's love affair with modular design means that the three main functions of the unit are on three separate boards- one for the drum voices, one for the rhythms and one for the rudimentary part sequencer. The voice board has trim pots for adjustments that could be broken out to the panel for more real-time control. The trigger inputs from the rhythm board are clearly marked on the voice board, meaning that it's possible to add external triggers for each voice. The roomy old-school board layout even hints at the possibility of replacing some resistors with pots and other mods to get even more out of the unit. Time will tell but I have a feeling this will become something really awesome.

The other big prize is the Leslie rotary speaker. With a few switches and a mains plug it could be driven by an external amp. With a little more work you could incorporate one of the amps from the organ for a nice Leslie combo. Add the reverb tank and the volume pedal and you'll have an awesome DIY guitar rig. The sky's the limit for how you can reuse and recombine this gear.

The bass pedals will probably become a lofi bass synth. I love nasty 555 square waves with FM. I'm also waiting on some 566s, which produce square and triangle waves. All you need is a resistor ladder and some trim pots for fine tuning and you've got a fun little bass synth. I might also try the resistor ladder/trim pot arrangement with an Arduino loaded with TobaTobias' Auduino sketch. Add the volume pedal to tweak the modulation and it would be a blast.

The keyboards are really heavy duty- nothing like the cheap plastic crap they foist on us today. They feel nice to play. I could see them finding their way into a DIY synth project real soon. I like the feel of these keyboards so much that I'm tempted to try to hack one into a midi controller for the Peavey Spectrum synth sitting on my shelf. At any rate they'll be a lot more fun to play around with than the usual yard sale and flea market keyboards I get to butcher.

So what else is there? Once again, Hammond's penchant for putting everything on a discrete board makes this a treasure trove for hacking and bodging. Most of the boards are labeled with their function, making it easy to play around. Even if the boards aren't directly reusable, they are full of quality components just waiting to be harvested. Instruments and audio gear always have the best quality components and are well worth the effort to strip. For more info on recycling components from circuit boards see my instructable here.

The voice select panel with its colorful plastic toggle switches is visually stunning. It's the same length as the drum machine panel and may come in handy when I mod the drum machine. I could see the switch panel becoming a basic sequencer using the bass and snare triggers or something.

I'm not an expert on power supplies. I use ATX PSUs from old computers and rescued wall warts for most of my projects. There are some interesting components in this power supply that may be worth stripping and anything with a coil gets thrown in a bucket for the next trip to the scrap yard. I also save old wiring harnesses for the same reason. Copper's worth money- just save it up until you have enough to make it worth taking in. If nothing else, just save your wire and coils until you have a bucket full and put it out on the curb- someone will take it. I never buy wire, I just save it from stuff I recycle.

Saving screws is more about me being stubborn and making a point than anything else, but the other hardware is useful to varying degrees. If your handy it's always good to have extra hinges and brackets around for repairs and projects.

So that takes care of the stuff that came out of the organ. Now what about the big, bulky wooden case? The one I have is veneered particle board and it's in rough shape so it's got a date with the Sawzall tomorrow, but an old organ could find new life as a desk, bar or planter. The way the drum machine bracket folded down and the keyboards folded up kind of reminded me of an electronic version of a Roentgen desk. With a little creative cabinetry I'm sure something amazing could be done. One of the big up-sells of the organ trade was the variety of materials and finishes used. I've seen old organs that looked really cool and would make nice furniture. If it's nice wood it could always be chopped up and turned into anything from a jewelry box to a ukulele. You might as well strip it like the Native Americans did the buffalo and use all the parts of the carcass.

So that's it. The organ has donated all of its organs and we're done here. Keep an eye out for more Instructables covering what I do with these parts as well as other fun stuff..