Although the top of the case became moderately warm under this harsh treatment, it was never uncomfortable to the touch. Price: $699.ĭuring the standard 1-hour preconditioning period at one-third rated power, the amplifier's fan switched to its high speed in about a minute, and it cycled between high and low speeds for most of the following tests. In addition to the power switch, the front panel has two pushbuttons that connect the two sets of speaker output binding posts to the amplifier outputs. Each channel also has a red Truclip indicator that lights only when the amplifier is driven into nonlinearity. Calibrations are also provided for 4- and 2-ohm loads. The led's, which are green up to 200 watts and red from 200 to 400 watts (into 8 ohms), are spaced at logarithmic intervals, with one-third of them assigned to power outputs under 1 watt. The front panel contains two rows of led instantaneous-power indicators, twenty for each channel. The black-finished amplifier measures 19 inches wide, 11-3/4 inches deep, and 5-1/4 inches high, and it weighs about 27 pounds. It is also rated for 300 watts into 4 ohms and 450 watts into 2 ohms. The Soundcraftsmen Pro-Power Four is rated to deliver 205 watts per channel into 8-ohm loads from 20 to 20,000 Hz with no more than 0.05 percent total harmonic distortion. An internal temperature sensor switches the fan to its high-speed mode when necessary. Instead of using large, heavy, and costly external heat-sink fins to dissipate the heat from the output transistors at high power levels, the Pro-Power Four uses a two-speed fan to keep them at a safe temperature.ĭuring normal operation the fan turns slowly and quietly, drawing outside air into the left rear of the amplifier, passing it over the internal heat sinks, and exhausting the warm air at the right rear. The Pro-Power Four has differential input stages, for low noise and distortion, and high-gain, fast-slewing Class A amplifying stages. This regulating action also minimizes the effects of reduced power-line voltage, which can seriously limit the maximum power output of an amplifier using an unregulated power supply. The PCR error-sensing circuits vary the conduction time of the power supply's silicon-controlled rectifiers, maintaining a nearly constant voltage under widely varying load conditions. When an amplifier is called upon to deliver a high audio power output, the large current drain normally causes the power-supply voltage to drop, reducing the maximum available power. The Pro-Power Four also features the proprietary Soundcraftsmen Phase-Control-Regulation (PCR) power supply first used in the company's PCR800 amplifier.
The amplifier uses no current-limiting circuits. The high-frequency response of its fully complementary mosfet output stages extends to beyond 10 MHz. Its ability to deliver high short-term current outputs (over 50 amperes, according to the manufacturer) into low-impedance speaker loads makes it compatible with many "difficult" speakers (such as the Acoustat or Apogee) that cannot be driven properly by most conventional amplifiers. Soundcraftsmen's Pro-Power Four power amplifier was designed to meet the extended dynamic-range requirements of compact disc players.