Product Review -
Adcom GFA-7000 Five Channel Amplifier - April, 1996
By John E. Johnson, Jr.
Adcom GFA-7000 Five Channel Amplifier; Five channel power amplifier; THX Certified; 130 watts rms/ch into 8 Ohms; Frequency response 10 Hz - 20 kHz + 0, - 0.25 dB; THD < 0.015%; Input sensitivity 1.14 volts; Input impedance 50 kOhms; Damping factor 800; Size 7"H x 17"W x 13 3/4"D; Weight 41 pounds; Black metal chassis; $1,299; Adcom, 11 Elkins Road, East Brunswick, New Jersey 08816; Phone 908-390-1130; Fax 908-390-9152.
As a follow up to the GFA-6000 five channel amp, the GFA-7000 adds THX certification and the prerequisite minimum of 100 watts rms into 8 Ohms. This unit is rated at 130 watts/ch continuous. Its modest price tag realistically suggests that it will probably deliver about 160 watts/ch before clipping (defined as 1% THD), as judged by our previous experiences. It has a 1.3 kVA toroidal transformer, a total of 120,000 uF capacitance, and a 63 volt rail, which represents a hefty power supply. Four Toshiba bipolar output devices per channel give the 7000 the designation "High Current". Although Adcom uses MOSFETs in most of their other power amps, giving a more musical sound, the bipolar output device amps are more suitable for current-demanding home theater setups.
The chassis is black metal, vented on top, with the Adcom signature horizontal lines embossed on the front panel. The on/off switch feels like it could be used to turn on the mains of a football stadium, and the room lights dim for an instant when the amp is powered up (another indication of having a big power supply). A single red LED in the center of the power switch indicates power on. There are also distortion alert LEDs (indicating transient clipping - 1% THD) and thermal protection LEDs which illuminate if any amp heatsink reaches 85 degrees C, at which point, that particular channel amp will shut down. It will turn back on when cooled. Both of these indicators are warnings that either the volume is too high, or the impedance is too low (too much current demand, which overheats the output circuits -this includes a shorted output, where the impedance is very close to 0), or both. The amp is fully rated into 4 Ohms (200 watts/ch), although it is rare that any particular setup would have 4 Ohm speakers all the way around. The 7000 is not rated for 2 Ohm loads, although it will drive 3.2, as per THX specifications.
The back of the 7000 has a DB-25 multi-pin connector for use with processors that have the corresponding jack. More likely, the five RCA input jacks will be used, and they are arranged, looking over the top at the back, from left to right, "L" for left front, "C" for center, "R" for right front, "LR" for left rear, and "RR" for right rear. The jacks are arranged along the top, spaced nicely for ease of connection. Underneath the input jacks are the corresponding speaker outputs, each of which is a binding post (red for positive, above the black for negative). Although the nuts are plastic, they are heavy duty, as are the posts themselves. They accept banana plugs, which we used for our tests. The nuts are also deeply indented, which makes them easy to tighten and loosen without fingers slipping.
We connected the GFA-7000 to a Parasound P/SP Pro Logic Processor, and a variety of speakers (Krix, Velodyne, B&W, Mirage), with Radio Shack Gold Patch interconnects, and Nordost 2-Flat speaker cable. Laserdiscs were played from our Pioneer CLD-3090.
With all laserdiscs we used, the Adcom GFA-7000 performed admirably. As I mentioned above, bipolar output device amps are not as musical as MOSFETs, but they have more power delivery when the need is there. Movie sound tracks are very demanding, and only at the very loudest passages, did the slightly gritty nature of the bipolars become evident. This is a matter of taste however, as it was not harsh, just a bit edgy, and it is a feature of the bipolar device. We never saw the clipping lights come on, and no wonder. A total of 650 watts available to power the speakers is plenty. The amp became only slightly warm, about the right temperature for an electric blanket on a cool Spring night. There was a slight amount of hiss, which is normal for power amps that have no input volume control. Even with a maze of interconnects, the hum level was quite low.
Our general opinion of the 7000 tonality is that it's neutral. No particular personality, and unlike people, that is the best kind of personality to have for an amplifier. The bass line was clean, mid-range natural, and highs crystal clear. It handled all of our reference speakers well, including the 6 Ohm variety. In a subsequent test, by passing the outputs of the processor through a crossover, sending all < 50Hz signals to subwoofers (front left/right to two Velodyne F-1500s, center to one Mirage BPSS-210, and sub-out to one M&K MX-5000), and all > 50 Hz to the main amp, the 7000 really sang without a stress or a strain at high SPL. The Adcom does not need this to strut its stuff, but we have found that just about any amp will do better by employing this technique (even though the main speakers might not respond to very low frequencies, the amplifier is still using some of its power in attempting to deliver them). This is quite a test, actually, because the incredible array of high end subs demands a good amplifier to match quality in the remainder of the spectrum, and the 7000 did just fine. One particular additional test we use is with an analog tape I made in Baltimore of several thunderstorms. Thunder is one of those sounds that has not only sharp transients, but, of course, deep, deep bass. Such sounds can make some amps and speakers fumble in the rumble, but the Adcom stood well to the mark.
In summary, the GFA-7000 represents a very nice addition to the Adcom line of amplifiers. It has just the right combination of build quality, power, sound, and price, to enhance any home theater. If you like sugar, perhaps a set of their MOSFET power amps will suit you better, but "Terminator 2" , "Diehard", and "Star Wars" fans can put the 7000 on their short list.
John E. Johnson, Jr.
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