---
title: "Building a Hammond organ to understand how it makes sound"
locale: "en"
url: "https://irz.fr/en/articles/hammond-reconstruire-pour-comprendre-en"
markdown_url: "https://irz.fr/en/articles/hammond-reconstruire-pour-comprendre-en.md"
category: "craft"
tags: ["music", "electronics", "instrument", "fabrication", "DIY"]
published_at: "2026-08-22T09:30:00.000Z"
author: "Léa Perrin"
translation: "https://irz.fr/fr/articles/hammond-reconstruire-pour-comprendre-fr.md"
---

# Building a Hammond organ to understand how it makes sound

Uri Tuchman built a simplified hand-cranked Hammond to show how spinning steel discs become musical notes — with no digital circuits at all.

The Hammond organ is an electromechanical instrument before it is a keyboard sound. The distinction matters because it explains why Uri Tuchman decided to rebuild one by hand rather than emulate it on a screen.[1](https://hackaday.com/2026/08/21/building-a-hammond-organ-to-understand-how-they-work/)

In a video published on YouTube, Tuchman constructs a simplified Hammond: a single octave, a hand crank instead of a motor, no Leslie speaker, no digital circuits.[2](https://www.youtube.com/watch?v=s0jEQ5Vdg3E) Just spinning steel tonewheels passing in front of magnetic pickups, and a keyboard that routes them to an amplifier. The result is enough to understand how the instrument produces sound, and why this 1930s machine still works.

## The tonewheel

The heart of the Hammond is a set of steel discs, each with teeth spaced to produce a sine wave at a precise frequency.[3](https://www.stefanv.com/electronics/hammond_tonewheel_capacitors.html) As the wheel rotates, its teeth pass a fixed permanent magnet. The varying magnetic field induces a tiny current in a coil wound around the magnet. It is the same principle as an electric guitar: a vibrating string moving past a pickup generates an electrical signal.

A full Hammond console contains 91 tonewheels.[3](https://www.stefanv.com/electronics/hammond_tonewheel_capacitors.html) Tuchman uses only twelve — one per key. The entire assembly is driven by a hand crank; in the original Hammond, an electric motor spins the wheels through a gear train.

What makes the mechanism oddly elegant is the absence of electronics between the wheel and the signal. No oscillator, no digitisation, no analogue-to-digital conversion. The pitch is directly physical: it depends on the number of teeth and the rotational speed.

## Teeth and precision

The problem with mechanically produced sine waves is that precision is almost impossible to achieve.[3](https://www.stefanv.com/electronics/hammond_tonewheel_capacitors.html) The teeth are not perfectly identical, rotation speed is not perfectly stable, and imperfections generate unwanted harmonics. A raw tonewheel signal is too rich in overtones to be musical on its own.

In the original Hammond, the solution is passive analogue filtering: a capacitor and an inductor (in the form of a transformer) form a bandpass filter that removes spurious harmonics and passes only the fundamental frequency.[3](https://www.stefanv.com/electronics/hammond_tonewheel_capacitors.html) Of the 91 tonewheels in a Hammond console, wheels 49 through 91 use this type of filter, with two standardised capacitor values: 0.255 µF and 0.105 µF.

Tuchman sidesteps this problem by CNC-machining his tonewheels. The teeth are precise enough to produce acceptable sine waves without additional filtering — at least at prototype scale.[1](https://hackaday.com/2026/08/21/building-a-hammond-organ-to-understand-how-they-work/)

## Drawbars and additive synthesis

What gives the Hammond its characteristic sound is not the tonewheels alone, but the way they are combined.[3](https://www.stefanv.com/electronics/hammond_tonewheel_capacitors.html) Each key activates several tonewheels simultaneously, and the drawbars — the sliders the organist pulls toward themselves — control the relative volume of each harmonic.

This is pure additive synthesis: start with pure sine waves and add them together to build a timbre. An 8-foot drawbar gives the fundamental, the 4-foot gives the octave, the 2-foot the double octave, and so on. The organist becomes the mixer of their own sound.

Tuchman's prototype omits the drawbars — each key directly activates its tonewheel.[2](https://www.youtube.com/watch?v=s0jEQ5Vdg3E) But the principle is the same: the sound is born from the superposition of physical frequencies, not software calculations.

## What the rebuild reveals

The reason Tuchman built this instrument is that abstract descriptions of the Hammond oversimplify how it actually works.[1](https://hackaday.com/2026/08/21/building-a-hammond-organ-to-understand-how-they-work/) People often say "it's an instrument with tonewheels" as if that were enough. But actually assembling the pieces — machining the wheels, winding the coils, calibrating the distances — exposes a number of constraints that theory does not show.

For example, rotational speed is critical: if the RPM drifts, the instrument goes out of tune. In an original Hammond, the motor maintains constant speed. In Tuchman's hand-cranked prototype, he plays with that variation to produce vibrato and gliding effects — turning a technical constraint into a musical possibility.[2](https://www.youtube.com/watch?v=s0jEQ5Vdg3E)

The other interesting detail is the total absence of electronics in the sound-production chain.[1](https://hackaday.com/2026/08/21/building-a-hammond-organ-to-understand-how-they-work/) No preamp, no signal processing. The magnetic signal is extremely weak — on the order of a few millivolts — and it is the external amplifier that does the heavy lifting. The Hammond is, in many ways, an instrument that produces very little on its own and relies on the rest of the chain to become audible.

## Why rebuild when you can emulate

There are dozens of plugins and digital emulations of the Hammond. Some are excellent. But emulation shows what the sound becomes; reconstruction shows what the sound is.[1](https://hackaday.com/2026/08/21/building-a-hammond-organ-to-understand-how-they-work/)

When you press a key on Tuchman's prototype and hear the note emerge from a spinning tonewheel passing a pickup, you understand something the plugin cannot transmit: the materiality of the process. The sound is not calculated — it is induced. It depends on speed, distance, tooth geometry, magnetic quality.

It is the same logic that drives people to rebuild typewriters, wooden solar systems or tube computers. Not because it is more efficient, but because the act of making is itself a mode of understanding. Rebuilding is a way of reading an object with your hands.

Tuchman's Hammond is not playable in the classical sense — one octave, a hand crank, no drawbars. But it perfectly documents the architecture of an instrument that defined the sound of jazz, rock and gospel for half a century, and still does.

## References

1. [Hackaday, Building A Hammond Organ To Understand How They Work](https://hackaday.com/2026/08/21/building-a-hammond-organ-to-understand-how-they-work/)
2. [Uri Tuchman, How does a Hammond organ make a sound?](https://www.youtube.com/watch?v=s0jEQ5Vdg3E)
3. [Stefan Vorkoetter, Hammond Organ Tonewheel Generator Capacitor Replacement and Calibration](https://www.stefanv.com/electronics/hammond_tonewheel_capacitors.html)