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RE/P Files: Electrotec’s System For Roxy Music, August 1983
New Lab-Q loudspeakers in operation at San Diego State University three decades ago...
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The Electrotec Soundcraft consoles have been designed to operate on 120 volts AC. Since most regions of this country have a slight variance in their available AC voltage, a Variac is put in the line which feeds the 12-volt DC power supply, to step up the voltage to ensure a consistent 120-volt source.

At the Roxy Music concert in San Diego attended by this writer, the available AC supply measured a slightly unsteady 118V—just low enough to possibly cause the consoles to lose headroom, and become unstable. To prevent problems, the Variac boosted the AC voltage to 123 volts; the unit also includes an AC power line monitoring meter, which is always handy to have around.

House Signal Processing
As supplied for Roxy Music’s house mix engineer Robin Fox, the Electrotec system was equipped with the company’s standard Brooke-Siren Systems Model 340 electronic crossover (Figure 4).

This device has a built-in limiting circuit on each pass band that is individually tuned for the affected frequency range. Input subsonic and high-frequency filters are offered with 24 dB per octave filter slopes. Crossover cards are of modular design.

Figure 4 (click to enlarge)

House equalization was accomplished through the use of White Model 4000 third-octave filter sets, which feature rotary-pot controls as opposed to a graphic layout. A White real-time analyzer provided Fox with an accurate display of the system’s frequency response and sound pressure level. An AKG C451E microphone supplied signal input to the analyzer, while an internal pink-noise source is available for system testing.

Other signal processing equipment in the house system included dbx Model 160 limiters for the main left and right outputs, and another pair of the same device for patching into the kick drum and bass guitar channels. Four Audio + Design Scamp Model 100 noise-gates were patched into drum input channels, and four Scamp SOl compressors were available for processing vocals.

Figure 5 (click to enlarge)

Special effects devices included a Lexicon Model 224 digital reverb, Marshall Time Modulator, Audio + Design Compex F760XRS stereo limiter, Eventide H949 Harmonizer, and an AMS Model DMX 1580S stereo digital delay. House processing gear was contained in three identically sized 19-inch rack-mount cases (Figure 5), and was tied into the house mix console via dedicated multipair cabling.

In the house system, playback of prerecorded music was accomplished with two ReVox two-track reel-to-reel decks and an Akai stereo cassette player.

Power Amplifiers
Electrotec has chosen the JBL Model 6233 as its exclusive power amplifier for both house and monitor systems. The Model 6233, because of its high-frequency switching power supply, weighs only 34 pounds per unit, yet develops 400 watts RMS per channel into a 4-ohm load.

Figure 6 (click to enlarge)

A total of 63 of these amplifiers were on the road with Roxy Music, packed three to a case: 18 for the monitor system, and 45 in the house.

Each amplifier rack has front-panel access to inputs and outputs, and AC connectors for each rack located at the base of the front panel (Figure 6). The 6233 amplifier contains one possibly unique design feature: a front-panel foam-lined vent provides flow-through ventilation to cover cooling requirements, so that units may be stacked directly one on top of another to conserve rack space with no ill effects.


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