Eliminating The Percussion Volume Drop

Originally From the OriginalHammondLeslieFaq

Before poking in your Hammond, please note that HammondsCanKillYou.

The most popular setting for the four Percussion switches in the B-3 family of Hammonds is the where all four switches are rocked toward the rear of the console. With this setup the percussion VOLUME switch is in the SOFT postion. When this switch is rocked toward the front of the console, the NORMAL position, the volume of the percussion signal increases while the volume of the drawbars signal decreases. A simple modification can be performed that will eliminate the decrease in the drawbar volume, while still allowing the volume of the percussion signal to be increased when the NORMAL/SOFT switch is set to the NORMAL position.

The percussion drawbar-volume drop is inherent in many organs, including ALL B-3, C-3, A-100, RT-3 and the M3. To solve this on those models, you can jumper out a resistor on the matching transformer assembly, which is the round metal-enclosed thing mounted on the upper right side (looking from the back) of the organ.

Don't confuse this mod with the ?PercussionVolumeMod which involves using a potentiometer to replace the resistor on the "percussion volume" tab. This Resistor is responsible for dropping the volume of the percussion signal (the "ping") when percussion is set to soft. That mod gives you an "infinitely adjustable" percussion volume. (Its R50 on an M3)

What we're talking about on this page is the volume drop of the rest of the drawbar tones of the upper manual when percussion is set to normal. Normally, the percussion volume is increased when the percussion tab is rocked from soft to normal, as expected, but... the drawbar (organ) volume is also reduced substantially!

Be sure you understand what this will do before you make any changes!

Luckily you can test this mod out Before you permanently alter your organ.

For a pictorial version of this mod on an M3 see PercussionVolumeDropM3.

First you need to get at the matching transformer. Its inside the aluminum enclosure under the lower manual drawbars, above the tone wheel cover on the right.

Remove the two screws securing the cover, and notice a group of resistors mounted on a strip on the left side of the matching transformers. The resistor to jumper out is the lowest one on the left (in a B/C-3, this is R1 (3.9Meg), in an M-3, it's R2 (1Meg)).

Use a clip-lead jumper first as a test.

To test what the jumper change will do before you solder it permanently, turn the percussion ON with the first 4 drawbars out to position 8. Hold a chord, listen for the percussion to decay, then while still holding the chord, rock the Percussion volume (not organ volume) tab from SOFT to NORMAL. Notice that the drawbar volume drops! This is normal in all organs of this type and is considered a serious drawback by many professional players. Most play the organ with the percussion tabs "four up" or all four tabs rocked up toward the rear of the organ for this very reason. This mod to eliminate the organ volume drop completely changes the way the organist can use the percussion!

Once you understand the original percussion situation, try this - add the jumper on the lowest resistor on the left, then hold a chord with the percussion on SOFT, let the percussion decay and while still holding the chord, rock the Percussion tab to NORMAL. You should now not have a drop in drawbar volume when you switch the percussion volume tab from SOFT to NORMAL.

There are several ways to modify the percussion even further, but this is the easiest way to get a fatter organ sound with increased percussion volume, and still keep the original SOFT position of the rocker switch volume capability.

TopicModification