Ondřej Kabrna Klavírista EN CZ

Dereux organ

5. June 2018

This one is only for “connoisseurs” in the area of old analogue electrical instruments :-)

I own a French Dereux organ with an electrostatic generator. Everyone knows the principle of sound creation with an electromagnetic generator (Hammond and alike), but hardly anyone knows today that in the 50s and 70s a few instrument types with an electrostatic generator were constructed. It is above all the Dereux speaking of the organ.

The electrostatic generator is a complex of 12 rotary silver-plated discs (12 as each one makes one halftone of octave) which rotate between stators on which there are pressed tracks that are a result of transferring time intervals of sound of real organ pipes. The particular discs and stators compose together complexes of variable condenser - thus the electrostatic generator. Therefore, these are something like analogue samples of real French pipes. Thus, the sound of instrument is incredibly authentic. The discs look like this:

I bought the instrument in a desolate state and unfortunately without the original cases. It did not actually play at all but I fixed all I could. I also redesigned something mainly for the purpose of safe operation (the internal direct voltage is almost 900V). In 2017, I made the cases according to what I had found about the original. Fortunately, I managed to buy a quite important component of original case: a difussor for high frequencies, thus a rotary speaking-tube above the speaker (clearly a copy of the Leslie system – yet only for high frequencies here). I designed the rest according to photos of original and since I like the “grand” organ sound, I used the 15´ speakers for the bottom and the top is therefore the original 4´. The amp (tubes, 100W) is uncommonly made for the impedance of 30 ohm – simply two cases with about 15 ohm into a series. I did not in fact want two huge cases as I would not be able to place them anywhere. Therefore, one case is high and the other has a separate bass and a separate top – consequently they fit next to the heating :-)) see the picture (I re-varnished the organ and attempted to make the cases look like half a century old – otherwise it is a decent pine joint filler - 28mm wide).

Despite various problems the instrument has, the sound is beautiful. In my view, it is far nicer than from digital samplers of pipe organ – see this short video here:

For those interested, I show the documentation that is commonly unavailable:

Check the inside of the generator – in operation:




All videos