My First Hammond Chop

Over the weekend, I chopped a Hammond Cadette for a friend. It was surprisingly easy… I didn’t bother to do any research ahead of time, and it still came out looking, functioning, and sounding great!

As you can see, this organ has several hinged pieces to make it easy to open up and modify. The electronics are very well laid out, as you’ll see.

The big accomplishment for this chop was to move the pedals to the lower keyboard (rather than eliminate them entirely). The Cadette is far from the top of the Hammond line, and it needs all the help it can get to sound good.

This is the block of contacts that control the pedals. They looked daunting at first, but then I realized that it was just a system to only allow one note to be played at a time. The colored wires are each responsible for a single note with one wire being the common ground (or signal, I didn’t care enough to check).

This pedal controls (well… controlled) the volume of the organ by using a light bulb and a photodiode. No kidding! You can see the tapered slot that sits in front of the detector in the center of the image (that thing with the cut wires sticking out of it).

The electronics attached to the pedal were quite small. I shorted the contacts where the photo detector would have been and moved the tiny board to the top section…

…right next to the spring reverb unit, which was originally located on the floor of the organ.

There is more than enough room for a lot of custom electronics in the top section.

After clipping all the pedal wires and running them up to the top section, I de-soldered the top 13 (1 octave plus the high C) keys and sandwiched them between 2 pieces of electrical tape. I’m not planning on reversing this mod, but if I get creative somehow I will have them where I need them.

You might ask, “Why not put the low notes at the LOW end of the keyboard?” Well, this keyboard starts on a low F, not a low C. Even if I started with the pedal’s F and wrapped the octave when I got up to C, I would still have the OTHER C with no place to go. Besides, the lower notes of the lower keyboard sound pretty good and I’d hate to lose them

With the styrofoam cover removed, I could work on the switch actions.

The trick here is that there is a different common wire for each keyboard, and they are not compatible. This probably has something to do with oscillators, but I’m taking the naive approach and just making it work.

The switch action is a round retaining bar (on the top) and a flat bar (on the bottom) that provides the electrical connection. These are held in position by a series of rubber “towers” that run along the length of the keyboard. I would need to cut the flat bar in order to split it between the original lower keys and the pedal keys I was adding.

Very fortunately, the rubber tower separated the top 12 keys from the rest, and there was an extra hole punched into the frame right next to it. So, I was able to cut the bar, move the tower, and slide both pieces back into the bar (being careful not to touch them together inside). Now both sides could have a separate common wire and were properly supporting their keys.

I soldered the new common wire onto the flat bar…

…and joined the other side to the appropriate place on the circuit board. I found this by tracing back the common wire of the pedal board, not because I have any ability in understanding complex electronic circuits.

Since the point of this modification was to remove the organ stand, I needed to put a bottom on the upper part of the organ so it could rest on an organ stand. Plywood does the trick, and I cut out holes for the 1/4″ out, EXT in, and the 4 bolts that keep the keyboards from swinging open.

Here’s Stu demonstrating the organ, the octave we moved, the difficulties of playing a keyboard with left and right hands swapped, and some cool effects: