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Product Review - Adcom 5500 and 5503 Power Amplifiers - September, 1996

By J.D. Moretti

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Adcom Amplifiers

Adcom, 11 Elkins Road
East Brunswick, New Jersey 08816
Phone 908-390-1130; Fax 908-390-9152

Adcom GFA-5500; Two channel power amplifier; 200 w/ch rms into 8 Ohms; Frequency response 10 Hz - 20 kHz plus 0, minus 0.25 dB (1 w/8 Ohm); THD < 0.18%; Input impedance 49.9 kOhm; Damping factor 700; Size 7"H x 17"W x 15"D; Weight 44 pounds; $999; Adcom GFA-5503; Three channel power amplifier; 200 w/ch rms into 8 Ohms; Frequency response 10 Hz - 20 kHz plus 0, minus 0.25 dB (1 w/8 Ohm); THD < 0.18%; Input impedance 49.9 kOhm; Damping factor 700; Size 7"H x 17"W x 16"D; Weight 57 pounds; $1,299

Adcom may very well be one of the most popular hi-fi brands in the United States. I see them everywhere. Not just at audio stores, but in my friends' homes too. They all seem to be quite happy with the various models they bought. We reviewed several in Secrets, and I don't hear any complaints. The GFA-5500 and GFA-5503 are two and three channel power amps respectively. They are designed for home theater, or at least the 5503 is (what else could you do with three channels?) Unlike the GFA-7000 [click here to see review], the 5500 and 5503 use MOSFETs in the output stage (the 7000 uses bipolars). MOSFETs sound more like tubes, and I like tubes very much (I use tube amps - an old Fender is my favorite - with my bass guitar). Of course, nothing but tubes sounds EXACTLY like tubes, but MOSFETs are supposed to come close.

These power amps are styled like other Adcom equipment (see photo). Black chassis, mucho heat sink area (about 650 square inches per channel), heavy duty on/off button. The face plate is embossed with horizontal lines (the panel is actually extruded). One could hardly call these amps "sleek", because they are very big. But when it comes to power amps, I LIKE big. In the case of the GFA-5500, there is a 1.5 kVA toroidal power transformer, and 2.0 kVA for the GFA-5503. Ten MOSFETs (five pairs) are used in the output stage of each channel. There are two sets of LEDs on the front of the 5500 and three on the 5503, with each set indicating distortion alert (when these blink, the amplifier output is approaching 1% THD, or clipping), and thermal protection (these indicate shutdown until cool). The back has a three-pronged grounded AC outlet, one RCA input jack per channel, and one set of binding posts per channel. That's it. No other switches (ground lift, bridging) or jacks (balanced inputs). They are no-frills power amps, and that's cool, because they sell for my kind of price. I don't have much cash, but I like lots of power, and the Adcoms have it.

One thing that I am always suspicious about when trying a new amp, is what it will do with low impedance loads. So, I connected the 5500 to our in-lab electrostatics, which go down to about 2 Ohms or lower. Then I put on some Bernard Hermann film scores and cranked it. I could get the distortion alert lights to blink, but only at high SPL (96.8 dB - 20.74 Volts - 3.016 Amps; SPL measured with both channels in operation, voltage and current measured from one channel). This is a real stress test, and I was impressed. It is obvious from the voltage and current measurements, that the distortion alert LEDs are set to blink when distortion is being approached - very conservatively - rather than when hard clipping occurs (which could damage the speakers). The Adcom engineers are officially California Dudes as far as I'm concerned. I wish I could put these amps in my van. I have four 15" woofers per side, and the impedance goes way, way down.

So, next I put the amps in with my home theater setup, and did they rock! I never could get the distortion alert lights to come on, and I played some loud sound tracks, like "Die Hard", and so on. I use 8 Ohm speakers in my home theater, and I recommend 8 Ohm to you readers too. With home theater, multi-channel amps, and kick-butt sound effects, the amps will perform at their best. With 4 Ohm speakers, and everything going at once, the distortion alert lights are more likely to come on. That's just the way it is. Even with 40,000 microfarads of capacitance per channel, and hefty toroidal transformers, those deep sound explosions and gun fire will demand extra current from all the front channels, and depending on how the director has set the rear effects, maybe from there too. So, for home theater . . . 8 Ohm speakers.

I took the amps back to the lab, and we connected them to a surround sound receiver that had pre-outs. This particular receiver has 100 watts to the front left/center/right, and 25 to the rear. We all felt that the inboard amps did an excellent job, but the dynamic range that the Adcoms provided was something else (the 5503 across the front left/center/right, and the 5500 to the rear left/right - giving 200 w/ch all the way around). I mean it was thunderous. We used them to review some new laser discs that had just come in. "Twelve Monkeys", "Dead Presidents", and "Broken Arrow". We did not miss any of the sound effects. I thought the walls were going to implode when the Stealth flew over Samantha Mathis' (what a FOX!!) head. These movies have deep, deep, DEEP foley, but those little yellow LEDs never lit up. I was really surprised. Usually, MOSFET amps clip sooner than bipolar output device amps of the same rated power, but the 5500 and 5503 are built like the jet engines that they had to deliver the sound for (I know, it's bad grammar to end a sentence with a preposition, but that's tough). And, we used 5 Ohm speakers (Krix). Even when we turned off the line level crossovers that shunt the <50 Hz to subwoofers, still no distortion alert LED action. So, my hat is off to the people in East Brunswick (I hate hats anyway). You know, maybe I should not have been so surprised. It used to be, and perhaps it is still so, that an amplifier could be gauged by its weight. Together, these two amps weigh in at more than 100 pounds (101 to be exact). That's only 15 pounds less than my wife. Although the amps got nice and warm with use, I still prefer her on a chilly night. Ahem, back to the amps.

Now, as to the musicality of the 5500, referring to when we had it driving the pair of electrostatics (Electrostatic Research Vistas), the amp produced a nice full bodied sound, with no edginess. I listened to a bunch of great CDs: Madonna, Steve Winwood, Bruce Hornsby, Clark Terry. The teeth were there in the sound, but no bite. Biting can be fun, but not with audio. Ahem, back to the amps. I could still tell the difference between these power punchers and my 6L6s, but then, my guitar amps don't have to reproduce the sound of helicopters exploding into a hillside. If you want all the dynamics that movies are capable of delivering, you don't need to look further than the 5500 and 5503, especially if you are planning on AC-3 and/or DTS, which need enough watts to make the room lights dim when cranked. All in all, these are really nice products, and they should not disappoint anyone who wants muscle in his/her home theater to watch Schwarzenegger rumble through "True Lies". At $2,300 for the pair of amps, they don't come cheap, but great sound with ample power they do have, and that is what we are looking for in the digital surround sound home theater of the near future.

J.D. Moretti


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