If It Ain't Baroque...

Okay, here are some more of the organ pieces-parts. These are not in chronological order. Everything was out of the organ case by the time these were taken, so I don't remember when they should come in order. Sorry.


Electronics sure have shrunk, haven't they? By the way, this is one of the percussion circuits.


A generally dark (and darkly general) view of the Leslie unit.


A look down into the rotor. There is a speaker in there somewhere! :-)


And finally, the motors. Yes, there are two of them here, one for each speed! Slow is on the left, and fast on the right.


The upper manual keys.


This is the upper manual keyer block. (The wires are supposed to be straight.) Horizontally, each wire is a note. Each vertical wire is for a different type of stop. So, when a key was depressed, all the wires in that column got pulled up together against another set of contacts (not shown,) but only the stops whose tabs were engaged would sound. I hope that makes sense...


The back of the upper manual keyer block. The flat tan things are early integrated circuits.


The filter circuits. These are passive (meaning they require no power) high-pass and low-pass filters for shaping the raw signal from the oscillators. Most consist of a coil, a capacitor and a resistor. High- or low-pass is determined by either the resistor or the capacitor being connected to ground. (I don't remember which is which.)


Another view of the filters.


The Oscillator. One of them, anyway. There are twelve altogether. They generate an harmonically rich waveform (probably close to a sawtooth wave) at a given pitch in three octaves. (In this case, the pitch is A.) The remaining two octaves provided by the manuals and the bottom octave of the pedal (16') are produced by the divide-down method* common in organs like this one.


The back of the oscillator circuit board showing (at left) where it was 'plugged in' to another board along with the rest of its brethren.


The oscillator divider boards for the manuals and the pedal divider. *Okay, more about the divide-down method. In this method of tone generation, the 12 oscillators produce the highest chromatic octave available on the organ. The raw signal is then sent to a divider circuit (which basically halves the signal.) This is repeated as many times as needed to produce all the notes. In this organ, the oscillators divide the signal down twice internally, so for these 5-octave manuals, only two more dividers are needed. The pedals require one more division of the signal, but since they are monophonic (playable only one at a time) the required circuitry is (obviously) different.


Upper left cheekblock with stop tabs and related circuitry. The white buttons at the far left are cancels.


Why Thomas made this an internal control rather than an external one is something I don't understand. Note that vibrato is DIFFERENT than Leslie Tremolo. Vibrato actually varies the pitch of the oscillators, while the Leslie system takes advantage of the Doppler effect to produce the warbling. Vibrato is electronic, tremolo is mechanical.


Preamplifier circuits. This is also where some signals are mixed before being sent to the main amp.


The lower left cheekblock with percussion controls, couplers, and another percussion circuit.


The bottom of the same, showing switches and electronics.


The lower right cheekblock with more percussion controls and output controls.


Such names! 'Vibraharp' is sustain for the gray (flute) stops, and 'Hawaiian Guitar' is the sustain for the red (reed) stops. The remaining three tabs control which sounds go to which speakers. The black switch at far right is the Leslie speed control switch.


Leslie motor switching circuit with capacitors on the power supply to keep the amp from popping every time you change speeds.