HAMMOND ORGAN

     Below is a schematic of a typical Hammond matching transformer. The primary winding has a relatively few turns of heavy wire and there are nine taps on the winding which are spaced logarithmically. The lowest tap is grounded, and the other successive taps represent increasing intensity levels, which you can see because the successive taps on the primary represent more and more turns of the primary winding. The signals from the harmonic controls on the console appear at various levels on the primary. They induce a corres-ponding signal in the secondary, which has many turns of finer wire.

     Because the secondary has many turns of finer wire, it has a much high impedance than the primary side. This high imped-ance is much more compatible with the inputs of the preamp-lifier and that is why this trans-former is referred to as a match-ing transformer, because it match-es the low impedance of the tone generator and keyboards to the high impedance of the pre-amplifier input.
     In a typical Hammond console there are actually two matching transformers, one for the top keyboard, and one for the lower keyboard and also the bass pedals.

Figure 14. Typical Hammond organ matching transformer.

     The reason for this is so that the musician can choose to have the vibrato effect on either keyboard independently. The very first Hammond organs had only a tremolo which affected the entire instrument. When the Hammond vibrato was developed, it similarly affected the entire instrument, but later on, the folks at Hammond devised the selective vibrato that the musician could place on either keyboard independently, giving him many more interesting tonal effects. Now, what exactly are tremolo and vibrato?
     Actually, there are several words which are sometimes used erroneously, so let's first clarify these terms.

Vibrato, Tremolo, Tremulant, Reverberation.

The first two refer to regularly recurring qualities which affect the tones of any musical instrument. The third, tremulant, is the mechanical device in a pipe organ which produces the first two effects, and the last, reverberation, has nothing to do with either of the first three words. But, because it sounds a little like the word vibrato, some people associate it either with vibrato, or use it erroneously when referring to what is actually vibrato. Reverberation is a prolongation of any sound which continues after the original sound has stopped. It is caused by repeated reflections or echoes of the original sound from the interior surfaces of a room or a hall, and generally increases in duration with increasing room size.

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