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Tonewheel Generator

The Hammond's sound source until 1975: a bank of metal tonewheels ("phonic wheels") spinning near electromagnetic pickups, each shaped to induce a voltage at a specific frequency — one tone per wheel.

How it works

  • All wheels are driven by a synchronous motor locked to the 60 Hz mains supply — which is why Hammonds hold pitch perfectly but only work where the mains frequency matches (50/60 Hz models differ).
  • Descends from Cahill's 1897 Telharmonium (alternator-based tone generation), miniaturized: Laurens Hammond replaced huge alternators with small wheels + an amplifier.^[raw/articles/wikipedia-hammond-organ.md]
  • Each note is a mix of wheel signals; the organ is thus a real additive synthesizer (see drawbars).
  • Keyboards derive notes from a 12-wheel master octave via gearing, adding characteristic crosstalk and gear-murmur that players now consider part of the sound.

Why it matters

  • The "warmth" everyone chases (including every clonewheel emulation) comes from this electromechanical imperfection: crosstalk between pickups, wheel flutter, key click from keying transients.
  • Hammond abandoned tonewheels for integrated circuits in the 1970s — the products flopped and the company died in 1985; the lesson: the flaws were the product.^[raw/articles/wikipedia-hammond-organ.md]