Stewart Audio World 1.2 Power Amplifier

by Roger Williams III

	Product Points
	Applications: Live sound; contracting and installation Key Features: High power output; compact, light weight package; balanced XLR and TRS 1/4-inch inputs; 1,200-Watt output at 4 ohms bridged; solid construction; good sonics Price: $999 Contact: Stewart Audio at 209-588-8111; or circle Reader Service 74.

Founded by Wade Stewart in 1982, Stewart Electronics develops innovative niche products aimed at the pro sound contractor and MI market. Early on, the company produced a variety of half-rack-space amplifiers, preamps and mixers that were later consolidated into a line of power amplifiers designed to deliver high power from a small, lightweight package.

Stewart Electronics (now Stewart Audio) was one of the first companies to adapt the high-speed switching power supply to audio power amplifier applications, reducing conventional power supply transformer sizes (and weight) significantly. The Stewart World 1.2 power supply - by virtue of its design - recharges 1,000 times faster than conventional Class AB types, thus requiring less space for storage (capacitors).

Although other manufacturers have introduced advanced designs - such as the Carver PT1250 or the QSC PowerLight - that are called "Pulse Width Modulated" or "Class H," the aim is the same: providing higher power at lower mass. Any road dog (and his chiropractor) will vouch for these virtues.

Features

The Stewart World 1.2 amplifier is a two-channel single rack-space unit that weighs 11 pounds, delivering 420 Watts at 4 ohms per channel and 1,200 Watts at 4 ohms in bridged mono operation. Frequency response is claimed from 20 Hz to 20 kHz with an A-weighted S/N ratio of 100 dB and a quick slew rate of 30 Volts per microsecond.

A high input impedance of 20 kilohms helps impedance matching with most available input sources. Current sensing circuitry detects when load impedance drops below 0.5 ohms and disconnects the power supply, protecting the unit and connected speakers until the perceived "short" is removed. At that point the amplifier will slowly ramp up to full power.

An inrush current limiting circuit minimizes power draw at initial turn-on, which may help to preclude the need for power sequencing devices.

The heavy, black-powder-coated aluminum faceplate features a centrally located power on/off switch with a red LED power indicator and detented level controls with a green LED -20 dB signal indicator and red LED clip lights for each channel. Massive heatsinks along the sides lead to the back panel. Each channel has a balanced XLR and TRS 1/4-inch input, connected in parallel to facilitate daisy chaining with other amplifiers if desired.

A bridge/stereo mode switch and 15-Amp breaker are to the left of the power cord strain relief. A pair of five-way binding posts for speaker connections and 1/4-inch phone output jacks are wired in parallel. The nearby binding post sets are conveniently to facilitate bridging with dual banana plugs.

The unit is solid and has a good fit and finish; indeed, prolific use of Torx-style screws prevented me from popping off the lid and checking under the hood, which chassis connection-straddling stickers warned against.

In use

I was anxious to test the World 1.2 with a pair of what I consider to be top-shelf compact speakers - Audio Composite Engineering 1160s. I was in a small club setting with an ensemble acoustic act. I had a Mackie VLZ mixer and Shure Beta 58 microphones for vocals. The Stewart exhibited exceptional control - punchy midrange and crisp, high-mid consonants for speech. An airy high-frequency quality nicely translated high E and B strings on an Ovation acoustic guitar via a Shure SM 81. In this application, I liked what I heard from the World 1.2.

I also had favorable results in my project studio, although the Stewart could not match the transparent sublime openness of my Hafler Pro 3000 through Tannoys - but this may be a case of apples and oranges.

And while I did not have the chance to try it as such, the World 1.2 would probably be a great fit for a foreground distributed system in a restaurant, club or multiple room residence - the sonic quality and ability to drive low impedance loads is certainly well suited for these uses.

Summary

At a list price of $999, and with all the advantages of power versus weight and size, the Stewart World 1.2 offers good value on the investment. With several application options, great sonics, solid construction and a three-year warranty, this amplifier is a quality option in a crowded marketplace.

Roger Williams III, a systems designer for MAS Audio, longtime NSCA, ICIA member and Syn-Aud-Con grad, is a regular contributor to Pro Audio Review.