Electro-Voice CPS-2
A fixed-installation amp with 850 watts of burst power, rack ears and a five-way protection system.
Overview
The CPS-2 is the middle model of Electro-Voice's Contractor Precision Series. It sits between the CPS-1 and the larger CPS-3 and CPS-4, in a lineup built for permanent installs rather than touring. Contemporary coverage of Electro-Voice's cartridge line in the late 1950s, as reported in High-Fidelity (April 1958, p.17), noted the company's push into popular-priced stereophonic reproduction - the same installer-focused sensibility that would later shape the Contractor Precision Series. The CPS Series was designed around the "unique needs of the fixed-installation customer," and the documentation is blunt about it. This is an amp meant to live in a rack, run for years, and survive conditions that would send a club-tour amplifier to the bench.
The headline numbers are respectable for the period. Electro-Voice rates the CPS-2 at 380 watts per channel into 8 ohms, 600 watts into 4, and 850 watts into 2, all measured at maximum power with both channels driven and under 1% THD at 1 kHz. The stricter rating, under 0.2% THD across the full 20 Hz to 20,000 Hz band, comes in at 300 watts into 8 ohms, 500 into 4, and 650 into 2. One is a burst number. The other is what the amp will deliver continuously across the audio band. Bridged, the CPS-2 is rated at 1,200 watts into 8 ohms and 1,700 into 4, which is enough to drive a single large subwoofer or a distributed 70-volt style load with headroom to spare.
The dynamic range is what separates the CPS-2 from a generic pro amp. Electro-Voice built the CPS Series around a "Nonlinear Signal Monitor," a dynamic limiter that caps distortion at under 1% and, in the company's telling, eliminates the hard-edged clipping that kills loudspeakers. The power supply is deliberately overbuilt for peaks. The manual claims burst output capability in excess of 130% over the amplifier's average continuous rating. Live music and speech carry high peak-to-average ratios, so that headroom keeps the amp from sounding strained. The other numbers: a 30 V/µs slew rate, total harmonic distortion under 0.05%, intermodulation distortion under 0.08%, and crosstalk better than 80 dB at 1 kHz. Input impedance on the balanced inputs is 20 k ohms.
The protection system is where the CPS-2 earns its install-grade reputation. Electro-Voice calls it a five-way system. It covers over-temperature, DC offset, excessive back-EMF from a failing speaker, low AC line voltage (brownouts), and the usual signal overload. Each of those is a real failure mode in a fixed install like a restaurant, a house of worship or a conference room, where nobody is watching the rack. The amp also includes audio limiters, peak current limiters, inrush current limiters, and a turn-on delay. Cooling is front-to-rear via a three-stage fan. Power requirements are listed as 120 V, 50-60 Hz, factory configured.
Connectivity is aimed at the contractor. Inputs are electronically balanced on XLR-type and Phoenix connectors, and the same connectors can loop the signal through to the next amplifier in the chain. Input routing switches let the user choose dual (stereo), parallel (monaural), or mono-bridged operation. Level controls are dB-scaled potentiometers on the rear panel, so there are no front-panel gain knobs to get bumped. The front panel carries an LED display that reports, per channel, whether the amp is operational, whether signal is present, whether the limiters are engaged, and whether any protection circuit has tripped. Outputs are 4-pole barrier strip connectors on Channels A and B. A ground-lift switch handles ground-loop hum, and the bridged-mode switch sits on the rear panel with everything else. In normal operation the CPS-2 will drive loads down to 2 ohms. Bridged, the minimum load is 4 ohms.
One quirk for anyone shopping used: the CPS-2's protection and limiter behavior is not adjustable the way a modern DSP amp's would be. The Nonlinear Signal Monitor is a fixed design. It does what it does, without user intervention. That suits install work and frustrates anyone who wants to tune the amp's behavior. The rear-panel-only level controls are the same kind of choice, made for a contractor and not for a studio.
The CPS Series shipped with a three-year warranty and what the documentation describes as extensive customer support. That is a sign of confidence for a product aimed at installers who can't afford a mid-job failure. It was never marketed as a glamorous amplifier. It's the kind of gear that gets bought in multiples, racked, and left alone for a decade.
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