A tonewheel organ with nine drawbars, built the way the instrument is wired: one generator running all the time, keys that switch onto it, and the percussion, key click, scanner vibrato and rotary cabinet that come after.
The idea
A tonewheel organ is not an additive synthesizer, and building it as one gets the sound wrong on the first chord. The real instrument has one shaft carrying 91 toothed wheels turning past magnetic pickups, and every key on every drawbar is a switch that taps one of those wheels. Drawbars models that shared generator, and its character follows from it.
Shared wheels. Play a C with the 4′ drawbar out and the C above with the 8′ out, and both come from the same wheel, in one phase at one level. They cannot beat against each other, which is why big chords stay clear instead of turning to mud.
No attack. The wheels never start or stop, so a key has no onset of its own. The only transient is the contact closing: the key click. Turn the click to zero and notes simply appear, which sounds synthetic because it is.
Foldback. The drawbars reach four octaves above the played note, but the generator only has so many wheels. At both ends of the keyboard a drawbar that asks for a missing wheel is wired to the same note an octave nearer the middle. The top octave stops getting brighter as you play up, and the bottom octave has no true sub-bass. Both are part of how the instrument feels under the hands.
Controls
- Drawbars 16′, 5⅓′, 8′, 4′, 2⅔′, 2′, 1⅗′, 1⅓′ and 1′, each from 0 to 8. 8′ is the played note; the others add harmonics above and one octave below it. The 5⅓′ bar sounds a fifth above the note, despite its number.
- Percussion adds a decaying ping on the 2nd or 3rd harmonic, normal or soft, fast or slow. It fires only on the first key of a phrase and re-arms when every key is released, so play detached to hear it on each note. Switching it on takes the 1′ drawbar out of the sound, as on the hardware.
- Key Click sets how much contact click starts each note.
- Vib/Chorus is the scanner: vibrato V1 to V3 or chorus C1 to C3.
- Rotary switches the cabinet between off, brake, slow and fast. The horn and drum speed up and slow down with real inertia. Rotor Depth and Mic Spread set how strong and how wide the effect is.
- Overdrive pushes the amplifier, and Level sets the output.
Getting started
Play Drawbars from your computer keyboard or a MIDI controller. Jazz Trio pulls out the first three bars, the most-played registration there is. Full Organ and Gospel Shout are loud and driven; Whistle shows foldback clearly if you play into the top octave; Percussive Third and Comp Chop are for rhythmic playing, and Brake Test is for hearing the rotors stop and start.
Drawbars currently plays in the browser only.
