Rotel RB-985 Amplifier
Rotel might not be as familiar to the general public as some other brands, but it is well known to serious audiophiles for the quality and value of its comprehensive line of audio products. Although manufactured in the Far East, the company's products are designed and engineered in Great Britain.
The RB-985 five-channel power amplifier is a recent addition to the Rotel product line. As the model number indicates, it is approved by Lucas-film to carry the THX logo on its panel. Each of its identical amplifier channels is rated to deliver 100 watts into an 8-ohm load, from 20 Hz to 20 kHz, at less than 0.03 percent distortion.
The RB-985 is a fairly large amplifier, whose 35-pound heft puts it into the middleweight class (by my definition, liftable but not something you would like to carry for a distance). Its exterior is all black, with extensive ventilation slots on the top, bottom, and side surfaces. The five amplifiers, each with four output power transistors mounted on a single heat sink, are operated from a single power supply built around a large and heavy toroidal transformer. Unlike many other power amplifiers, the RB-985 has a well-filled interior, with several large circuit boards and a notably clean, uncluttered layout.
The amplifier's front panel gives few clues to its special qualities. Aside from the THX logo, a pushbutton on/off switch, and a small, red pilot light, its only visible feature is a vertical row of small LED protection-indicator lamps numbered 1 through 5. A preliminary examination of the amplifier's interior revealed at least fourteen fuses, and there may have been other protective circuits that were not easily identifiable. Our tests were without mishap, however, so we were spared the need to identify or correct any problems.
The RB-985's rear apron, on the other hand, tells you unequivocally what it is meant to do. Along its lower edge are three groups of multiway speaker-output binding posts (which accept wires, lugs, or banana plugs). Above each group are the corresponding gold-plated input jacks (standard phono jacks). At the left and right sides of the rear panel, the speaker outputs and signal inputs are identified as for the surround and front channels, respectively. In the center of the rear apron is a group consisting of two sets of speaker-output jacks and a single input jack, all designated for the center channel. All the speaker binding posts are color coded (red, green, blue, or black) to identify their function and simplify installation.
Like some other Home THX-certified components, the RB-985 also has a computer-style DB25 multipin connector on its back panel. If your surround processor or preamp is a Home THX model that also has such a port, you can connect it to the amplifier with a single cable, eliminating the five separate RCA cables that would ordinarily be required. No more double- and triple-checking to insure that inputs and outputs are properly matched - a five-channel home theater hookup actually becomes easier than an ordinary two-channel preamp/power-amp connection.
We tested the RB-985 while driving three channels simultaneously, but since they are identical, we made measurements on only one of them. Driving all five channels to reasonably high levels was not practical for logistical reasons (simply because it's hard to find room for five bulky, heavy, and hot load-resistor assemblies in a relatively limited space).
The standard FTC preconditioning period of 1 hour with the channels driven to one-third of rated power made he amplifier rather warm, but not uncomfortably hot. Later, when it was driving 4-ohm loads (the lowest load impedance Rotel recommends for use with the RB-985), its exterior became still warmer, though not dangerously so.
As our test data show, the Rotel RB-985 is a real powerhouse of an amplifier, rated quite conservatively. It easily met or surpassed its specifications, with no external indication that it was anything unusual for a conventional amplifier of its size to deliver (at times) as much as 500 to 1,000 watts into 4-ohm loads. I am quite sure that if sufficient high-power load resistors had been available it would have performed consistently with all five channels operating simultaneously.
Actually, the use of identical amplifiers for all channels is probably overkill for a home theater installation, since unless the surround speakers are quite a bit less sensitive than the front speakers they should never require as much power (and certainly not for enough time to require such a robust amplifier as the RB-985). Other applications can be imagined, however, in which having five separate high-power amplifier channels available would be handy, especially when the entire package is no larger (and not much heavier) than an ordinary stereo receiver.
Considering what it does and how well it does it, the Rotel RB-985 is an excellent value. Past experience with Rotel products also suggests that it is likely to keep on performing well for a long time.
