If you're technically competent, or have someone else who is, and can refer them to this page, it lists a few changes that you can make to the organ, if you feel the need.
Extra outputs
In recent years I'd been making recordings to collaborate with other musicians during the 2020's plague shut-ins. Originally you have two options, record from the RCA line outs, or mike the organ up.
The direct outputs aren't very good, they lack the resonance of the organ's amplified speaker system, and they're unbalanced signals (not always a problem at home, but can be when you have long leads and lots of things connected together).
Miking the organ can sound better (and always did in my case), but you have to contend with other surrounding noises (I usually just drowned them out by playing loud), and room resonances can do horrible things with the bass. Not to mention it can be a faff working out where best to place the mikes, with lots of test recordings.
My eventual solution was to mike the room, in general. And add direct feeds for a few things so I could could change their levels in post production (chiefly the pedal voices and the drum unit), and to add balanced outputs to the existing stereo outputs.
This involved mounting a series of ¼″ TRS phone sockets on a metal panel, and mounting them under the keydesk behind the existing connectors. The jacks connect to audio-coupling transformers mounted on a board inside the console near the output section, with the other side of the transformers connected to the RCA stereo output jacks, and various points on the circuit boards.
While I could direct connect to these points, going through audio transformers provides a degree of isolation that protects the organ circuits, as well as providing balanced outputs. And you can still easily connect to unbalanced equipment just by using a TS guitar lead instead of a TRS patch lead, without causing any problems.
Since my aim was to aid in post-production, and many of these signals don't really change with the dynamics of songs, they're mostly pre-expression-pedal-controlled feeds (fixed levels). This means as you make the melody louder or softer, the drum unit and bass levels don't change. Internally, the organ is somewhat similar, the expression control voltage to those sections is modified, so they're effected less than the rest of the organ by the expression pedal.
I also experimented with tapping into the switching feed for the fake Leslie, it is possible to make a tab-voice output to feed to a real Leslie, or a better Leslie emulator. Though this organ's attempt at faking it, by amplitude and phase modulating the sound between two speaker systems on the corner of the organ with BBDs (bucket-brigade-delays) and VCAs (voltage controlled amplifiers), isn't too bad if miked in the right spot (somewhere beside, and perhaps behind your left foot). It's the same technique as other emulators, they just use better and/or more BBDs, with more tweakable parameters.
There are various useful tap-off points on the RME (reverb and mixing) board. Some connections should be AC coupled through a capacitor, first (check for DC voltages with a meter).
| Pin 1 | Drum unit left into RME board |
| Pin 2 | Drum unit right into RME board |
| Pin 30 | Pedal tones into RME board (straight, no effects) |
| Pin 54 | Spring reverb tank amp output into RME board |
| Pin 57 | Driver signal to the spring reverb tank |
Certain points are also good break points. Such as you can tap-off the drum unit signal coming into the RME board, and interrupt it, so you can keep the drums out of the main signal. This allows separate recording, and using them as an un-heard metronome.
Yes, the drum unit is in stereo, with various parts of it spread around as if you were sitting at the drummer's stool.
The reverb tank output lets you separately record the spring reverb, giving you much more control over it. Alternatively, you could feed the organ to a more sophisticated reverb unit.
| Pin 1 | Organ tones feed into Leslie emulator |
| Pin 4 | Organ tones to Celeste effect generator |
| Pins 14, 15, 16 | Triphonic Celeste effect output to RME board |
| Pins 22 & 23 | Stereo output of Leslie emulator to RME board |
Interrupting the fake Leslie signal path allows you to use an external emulator, instead, and still use the console switches to switch it in and out of circuit. Likewise with the Celestes.
An organ celeste effect is a slow chorus rippling phase delay, not an orchestral Celesta instrument. It's supposed to emulate the twin sets of slightly-out-of-tune-with-each-other pipes on a pipe organ (that work the same way as the slightly-off tuning of half the strings on a 12-string guitar), but really just sounds like a bad synthesiser string ensemble effect (which is doing the same multi-channel, multi-variable-phase delay effect, but usually in a nicer sounding way).
There are several set of Celeste effect BBDs. One for the upper, lower, and pedal organ tab voice tones, another for the string ensemble (this is separate from the string tab voices), another for the vocal ensemble (really just a reedy weak horn voice).
I may add notes about more tap points as I look through the service manual, but the RME board ones are the only ones I actually bothered to use.