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The Electronics

The sound generation and processing electronics comprises about 60,000 discrete components, most of them on approximately 150 circuit boards. (The background image on this page shows a small subset of these boards.)

The large majority of these boards are dedicated to generating the basic notes. The generator boards each encompass one octave, the twelve notes from C to B. (If you are unfamiliar with music notation, that statement may seem a bit strange. Find a musician friend to explain it to you until I get around to putting an explanation on this site.) For each of the five pedal ranks, one of the three generator boards only has eight notes (C - G), since the pedalboard encompasses only two and two-thirds octaves. For the technogeeks out there, here are the gory details of the circuitry.

Several generator boards are coupled together to form a "rank". One rank generates all of the notes for a given set of tones (voices) from the lowest note to the highest note. For pedal ranks, this is 32 notes. For regular manual ranks, this is 85 notes (61 keyboard notes plus an octave lower and an octave higher to accommodate couplers.) The four unified ranks, (playable from all manuals and pedals, and the source of mixtures and mutations) comprise 96 notes each. (There will eventually be a link here to more detailed explanations of this.)

Each rank of generators is connected to a tone changer board, each containing up to eight tone changers. Each tone changer is a special filter that modifies the tones coming from the generators. During the years the Park organ was built, the Artisan Organ company (upon whose kits the instrument is based) redesigned the tone changers, so this organ includes some of both styles of tone changers. Gory details for gear-heads.

The unified ranks each have only a single filter, one each for the four basic tone families: Diapason, Tibia (flute), Viola (string), and Tuba (reed). In general, the unified ranks can be played from any of the five claviers and at a variety of pitches. For example, the Tibia rank can be played on the great manual at nine different pitches, from 16 foot (the low C key produces a 32 Hertz tone) to 1 foot (the low C key produces a 512 Hertz tone, or four octaves above the 16 foot pitch).

The manual ranks each connect to a tone changer board with eight individual filters, thus each manual rank produces eight distinct stops or voices. These eight stops typically include two voices from each of the four tone families, but there are several exceptions. There are pros and cons to deriving multiple voices from a common set of generators. The major advantage is low cost, but one loses some richness of sound (the "chorus effect") when selecting multiple stops derived from the same rank of generators. The 8 foot swell rank actually has two tone changer boards, thus produces sixteen voices.

The pedal ranks each connect to a tone changer with six voices (one diapason, two flutes, one string, and two reeds), except for the 32 foot rank, which only generates two voices, a reed (Bombarde - I always liked that name) and a flute (Contra-Bourdon).

The audio signals from the tone changers are routed to voltage-controlled amplifiers. The amplification factor of these is adjusted by the expression pedals to increase and decrease the loudness of all ranks on a given manual. From there, the signals go to the main power amplifiers and on to the loudspeakers, which convert the electric signals into acoustic signals.

In addition to all of this, there are multiple power supplies which create the various voltages necessary to run the entire show. The keying voltage to the generators is 75 volts, the tone changers require not only 75 volts, but also +12 and -24 volts. All relays (for the coupler actions, the stop presets, and eventually for the valves in the windchests) require 14 volts. In addition to all of this, most of the peripheral devices have their own power supplies. As the instrument is modernized, additional power supply levels will be required, probably + and - 15 volts for operational amplifiers and + 5 volts for digital circuitry (microprocessors, etc.)

This page last updated at 3:03 PM on Mon, Apr 23, 2007
CHORD site maintained by Dr. William Park. Please address comments or suggestions to parkw@ces.clemson.edu