Product Review - Rotel RB 985 Five Channel Power Amplifier - September, 1995 By John E. Johnson, Jr.
Five channels of amplification, THX certified, 100 watts rms output per channel at 8 Ohms, Frequency response 10 Hz - 80 kHz plus or minus 0.5 dB, harmonic distortion less than 0.03%, input impedance 27 kOhm, damping factor 180, size 5 1/2"H x 17 3/8"W x 15 5/8"D, weight 34 pounds. Black metal chassis, non-grounded AC plug. $999. Rotel of America, 54 Concord Street, North Reading, Massachusetts 01864, Phone (508) 664-3820.
Rotel is no newcomer to audio electronics, having been in manufacturing for more than 30 years. The RB 985 is their multi-channel power amplifier entry into the home theater market. Our unit for review arrived in a carefully insulated double carton which gives it some added shielding to bumps and knocks in the delivery van. It is, like many such units, contained within a black metal chassis, having an on/off switch on the front, and five LEDs which flash at power on, and then turn off to indicate all is well. They will light if there is an overheating problem or shorted outputs. Thus, the unit appears from the front as unobtrusive and blends well into any hi-fi home theater system from an appearance standpoint.
The rear of the unit has the input jacks (RCA unbalanced) arranged, from left to right (looking over the top at the back of the amplifier), as left rear surround, left front, center, right front, and right rear surround. There is also a multi-pin port on the rear for connecting the RB 985 inputs using a single cable which would contain all the leads from the surround sound processor/preamplifier. This saves having to weave your way through five separate cables that would otherwise be necessary for connecting five RCA output jacks on the processor to the five RCA input jacks on the RB 985. Of course, the processor must also have the appropriate multi-pin port. Such processors are on the way to your local dealer now. The three-way binding posts for theoutputs to speakers are arranged in the same order, underneath the respective inputs. The outputs are color coded with blue, green, and red posts for the positive leads, and black for the negative. This helps a bit when leaning over the amp to make speaker connections. The metal threaded posts are a little thin for our tastes, as they are easily bent if the user is not careful.
Beneath the hood lurks a big toroidal power transformer (shaped like a doughnut). Toroidal designs are quite vogue these days, having greater efficiency for their size, compared to the older style iron core types. There are four bipolar output devices (transistors) per channel. There are no individual input level (volume) controls for the channels. We prefer input level controls because they allow more flexibility in adjusting the balance of sound in the room - not necessarily a feature available on every surround sound processor. Also, the AC input plug is ungrounded. The amp, thus, is very basic - no frills, no flash - just plenty of power (a total of 500 watts rms). It is THX certified, meaning that the amp has at least 100 watts rms per channel for high intensity sound tracks all the way around. This will become even more important should you buy this amp for AC-3 use.
We connected the RB 985 to one of our reference systems, and began the test with "Jurassic Park" (our reference for all surround sound systems) on the laserdisc. We also tested the amp with "Drop Zone", "Murder in the First", and "Solar Crisis". CD's included "The Great Fantasy Adventure Album", "Tony Bennett - Unplugged", and "Madonna - Like a Prayer". The opening scene from Jurassic Park is a good test for any system. There are men shouting, cranes groaning, trumpets (musical score) blasting, and a carnivorous dinosaur breathing heavily. As with all our test units, we cranked the RB 985 up to window rattling levels, and only at the outermost regions did we sense that the Rotel was being overdriven, as evidenced by a slight harshness to the trumpets . Of course, none of us watch movies on a routine basis with the volume control at this level, but it is a test we perform on review equipment to determine how far the electronics can be pushed. At more typical volume settings (the "realistic" kind of volume level for family viewing - not really loud, but not at a level you could answer the phone either), the Rotel performed beautifully, with a clean, crisp, sound quality. Thus, 99% of the time, harshness is not an issue. Other multi-channel amps rated at nearly this same power might deliver higher volumes without distortion, but they have more costly power supplies. Although driven hard, the RB 985 never overheated - in fact, it merely got warm. This is testimony to an efficient design, as the heat sinks are not very big. I asked Jeanne Fairbrook and one of our referees, Alex Samet, to listen to the home theater system with the Rotel connected, not informing them which component was under review. The question was, "How does this sound compare to what you are used to at the cineplex?" They both said that this system was better than anything they had ever experienced at a commercial theater.
Thus, at less than a kilobuck, the Rotel RB 985 delivers more than your money's worth and is one fine little package that will fit nicely into any home theater system. (Did I say "little"? This 34 pound component will still send me to the chiropractor if I am careless when moving it.) The only suggestion we could make for improvement, without involving a significant increased cost, is to make the color coding on the speaker binding posts the same for each channel type (surround and front channels) rather than mixing the colors, and to beef up the binding posts themselves with thicker metal.
Summary (Five stars is highest rating):
Sound Quality: Construction: Value: Pros: It delivers excellent sound within its power supply limitations.
Cons: No input level (volume) controls for individual channels. Speaker binding posts are lightweight.
John E. Johnson, Jr.
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