Changing The Percussion Keying Source

From the OriginalHammondLeslieFaq

When Percussion is enabled, one of the harmonic busbar contacts from each key is used to trigger the Percussion amplifier. This removes one drawbar harmonic from the palette available to shape the sound. The stock setup removes the harmonic available at the 9th drawbar. Some players prefer to have the top-most drawbar available at all times, even when Percussion is enabled. This modification to the percussion circuit changes the percussion amplifier's trigger source from the 9th harmonic busbar to some other source, usually the 8th.

The following procedure has worked on a B-3, C-3, and A-100. You will probably want a copy of your organ's schematic and wiring diagram for reference.

Note: All references to soldering on drawbars are in reference to the Upper Manual "B" Preset group, which is the 2nd group of nine from the left, when viewed from the console seat.

Identify the following

Resistor Panel

A phenolic board measuring about 1" X 5" is mounted to the rear of the upper manual just below the upper manual "B" preset drawbars. This board is called the resistor panel. On the left side of this panel are three dual-mounting lugs. Each of the dual lugs has two wires attached of similar color. One dual-lug has two white wires, one has two green wires, and one has two yellow wires.

Preset Bundle

A bundle of nine multi-colored wires comes from the upper manual "B" preset key. They exit the upper manual behind the preset panel (metal bars with lots of screws). This bundle will be called the preset bundle. Six of the wires in this bundle are routed up and immediately below the drawbars, where they breakout of the bundle and are soldered to the drawbar ends. The remaining three of the bundle are routed below the drawbars behind the upper manual and attach to three of the dual-lugs on the resistor panel.

The other wires of similar colors (to those from the preset bundle) on the resistor panel come from the Percussion Switch assembly.

The Procedure

1. Unsolder the gray wire from the 8th drawbar.
2. Unsolder the white wire from the 9th drawbar and solder it to the 8th drawbar. This white wire goes to the percussion switch and this now configures the percussion to trigger from the 8th drawbar key contacts.
3. There are two white wires soldered to one of the dual-lugs on the resistor panel. This is the left-most lug on my A-100's Resistor Panel. One of the white wires comes from the Percussion switch and one comes from the preset bundle. Identify and unsolder the white wire that comes from the preset bundle (routed from behind the preset panel) that is attached to a dual-lug on the resistor panel.
4. Solder the gray wire, removed in step 1, to the resistor panel at the point where the white wire was removed in the previous step.
5. Solder the white wire, removed from the resistor panel in step 3, to the 9th drawbar. Splice a short length of wire to it if it's not long enough.

HammondModifications