Electronic organs - circuits, experiences and interests

[Lucien Nunes]

found this very good explanation: https://www.jayharrisonaudio.co.uk/post/...o-of-three

There are a couple of minor errors there. It references my own site but has also borrowed one of my pics. My original blurb is here and on associated pages:
http://www.electrokinetica.org/d8/2/index.php

It is really amazing the complication of these organs

You haven't seen some of the most complicated bits yet. The underlying reason is that the pipe organ has at its core a very large number of independent and independently-controllable sound sources. Electronic emulations therefore also need a large number of independent sources and the means to bring them all under the control of two hands and two feet.

A few years ago I did a write-up on another forum under the title '193 valves in 5 days' about a quick turnaround of a Miller organ from the early 1960s based on independent valve oscillators. Between the 4 ranks there are 29 octaves (= 348) of generators each using half an ECC82, each producing two waveforms, for a total of 696 tone signals. There were a few larger examples but this was pushing the limit of practicality at the time. Depending on model, Hammond tonewheel generators produce between 82 and 96 tones. The small Compton generators produce 84 tones, larger models usually either 252 or 324, although not all independent in phase as are the Miller's oscillators, a point we'll return to later.

Very convenient wiring for tracing Lucien. Blue goes to blue, to blue :-) I hope they are number coded.

As with most pipe-organ wiring, extensive use is made of strict lacing of the wiring looms so that every core is tied out in numerical order. Identification is then by position in the loom rather than colour or number. Historically the wire was double cotton-covered and all white. Compton were very early adopters of PVC insulation, for example on the polarising circuits of Electrone generators where high insulation resistance is desirable. In these they usually wired C's in a contrasting colour for speed of tracing, e.g. if you want to find middle G# you count along 3 C's and 8 more wires. The 18V DC action wiring was often still DCC-insulated due to the much smaller radial thickness leading to more compact looms.

3 Pics from the Compton Draper organ:

Cut cable loom. This is one disadvantage of not using colour codes. This should never have been cut, it's the main loom linking the console to the generator rack in the Draper organ, about 275 cores. This was done before I bought the organ, as the people moving it wanted to detach the generators to make it lighter. They assumed I would be junking them and converting it to a digital, instead of restoring it (why would you do that?). Had they been disconnected at the test board, it would have been simply a matter of reconnecting as the lacing would have preserved the identity of every wire.

Another pic shows 18V action wiring in DCC 26SWG on the back of the combination setter board, where there is one wire per stop per piston.

Then we see the back of a 61-note 13-bar key relay. Note the DCC loom for the 18V magnet wiring along the top, which is a small part of the large loom from the console to the generator rack. Then in the yellow polarising feed loom to the generators the C's are in blue, and on the white relay diagonal crosswiring itself the C's are red.