Technics SA-GX650 AV-receiver
Heading Technics' new line of audio/video receivers, the SA-GX650 is a powerful and versatile component that should be equally at home in surround-sound, home theater, or conventional stereo applications.
The SA-GX650 has three 100-watt amplifiers, for the front left, center, and right speakers, and a 45-watt amplifier for driving a pair of rear (surround) speakers in a Dolby Pro Logic surround-sound setup. There are also line-level outputs for driving one or two subwoofers through an external amplifier. In the Dolby 3 Stereo mode, the surround-channel signal of a Dolby-encoded soundtrack is folded into the front and center speakers. This mode is recommended for home theater systems with a center speaker but without surround speakers. In the receiver's conventional stereo mode, only the left and right front channels are operative, and their power rating increases to 125 watts per channel into 8 ohms from 20 Hz to 20 kHz with no more than 0.05 percent total harmonic distortion (THD).
The SA-GX650 is a fairly large receiver whose front panel contains a central display window and a considerable number of pushbutton controls. The eleven preset buttons, in a row just below the window, can store and retrieve the frequencies of up to thirty FM or AM stations. Underneath is a second row of buttons that select the operating mode (Dolby Surround, Dolby 3 Stereo, or stereo), activate the Dolby Pro Logic calibration tone, adjust the relative levels of the center and surround speakers, select the Pro
Logic center-channel mode (Phantom, Normal, or Wide), adjust the Pro Logic delay line (from 15 to 30 milliseconds in 5-ms increments), and switch the loudness compensation on and off. Small round buttons select AM or FM and stereo or mono reception (the reception mode is normally set automatically).
Large square buttons near the bottom of the front panel select the program source. Inputs are provided for two VCR's (one of which is also accessible from the front panel), audio recording (with monitoring), CD, and phono. There are also a front-panel headphone jack and small knobs for the bass and treble tone controls and balance adjustment.
Although there are quite a few buttons on the receiver's panel, most are small and inconspicuous, and they are arranged in a logical pattern, making the SA-GX650 more comfortable and less confusing to operate than most other A/V receivers we have tested. The display window is .exceptionally clear and informative, providing all relevant information on the receiver's operating status without unnecessary confusion.
The receiver's two most conspicuous controls, which overshadow the many smaller ones, are the large knobs flanking the window. At the right is the volume control, which is motor-driven when operated from the remote. A muting button next to it reduces the volume by about 20 dB. To the left of the window is the tuning control, easily the handiest we have seen on a receiver in recent years. It can be operated in two distinctly different modes, selected by a nearby button. In the automatic mode, a slight movement of the knob initiates a scan of the currently selected radio band, up or down in frequency depending on which way the knob is turned, until a station is acquired. In the manual mode, the tuning action resembles that of an analog tuner (very few of which approach the smoothness of the SA-GX650), with a very light "feel" and a swift coverage of the entire tuning range. Since the slightest touch can shift the tuning knob's setting, a third mode (lock) disables it when desired. A single small button next to the knob toggles between the tuning modes, which are clearly identified in the window. Another button lets you tune in a frequency by sequentially pressing the numbered preset buttons.
Finally, there are two small speaker-selector buttons. In stereo mode, they channel the signals to either or both of two pairs of main speakers. Normally, the SA-GX650 is rated for operation only with loads of at least 8 ohms. But if you wish to use one pair of 4-ohm speakers (which require more operating current), the receiver can be set for this heavier load by simply pressing and holding one of the speaker-selector buttons (it is not possible to use two pairs of 4-ohm speakers simultaneously).
As our test results show, the SA-GX650 can deliver very high outputs under some conditions. In addition to electronic overload protection, which instantly shuts down the receiver when its survival is threatened, a cooling fan draws outside air in through slots on the top cover, passes it over the fins of the internal transistor heat sink, and exhausts the hot air from the rear apron. The fan is thermally operated and comes on only when needed, so that its noise (which is audible, though not to an annoying degree) will not be intrusive. Normally, the fan will operate only when the system is playing at a level that would completely mask its sound. But even at lower levels, when it is not operating, the top of the cabinet becomes quite warm.
Although the rear apron of the SA-GX650 has all the necessary input and output connectors, it seems almost sparsely populated in comparison with other A/V receivers we have tested. In addition to the obvious input jacks (and outputs for one of the VCR's and the audio recorder), there is a TV-monitor output, two subwoofer line outputs, and an output for a remote-control connection to a compatible Technics tape deck or CD player.
Surprisingly for a receiver of its power capabilities, all of the SA-GX650's speaker outputs except the one for the center speaker are snap clips that accept only stripped wire ends. The center-speaker connector is a spring clip. Although these connectors are probably adequate, they don't allow the use of heavy-gauge wire, spade lugs, or other conventional high-power connectors such as banana plugs. There are two switched AC outlets on the rear of the receiver.
The SA-GX650 comes with an AM loop antenna that mounts on the rear apron and can be pivoted over a 180-degree arc. Binding posts are provided for 75- and 300-ohm FM antennas, but there is no F connector.
The receiver has a versatile remote control that not only duplicates most of its key front-panel features but serves as a system control for associated compatible Panasonic or Technics components, including CD players, VCR's, and TV receivers, as well as VCR's and TV's from Zenith and RCA. (We tried it with an RCA TV we have had for a number of years, and it worked perfectly.) In addition, the remote can "learn" to control TV's and VCR's from other manufacturers.
The performance of the FM tuner section was comparable to that of many moderate-price stereo tuners and receivers. Although its distortion was not particularly low, it should not be audible with music (and wasn't, in our tests). Interstation muting is on during FM tuning, but while a station is tuned in, a reduction of signal strength or removal of the antenna will produce the familiar hiss of an unmuted tuner. In stereo reception, the 19-kHz pilot-carrier leakage into the audio was very high (evidently there is little or no filtering), inflating stereo noise and THD plus noise measurements. The leakage could also cause problems if you record stereo FM broadcasts onto analog tape or reduced-bit-rate digital media such as MD or DCC.
Most other FM-tuner performance characteristics, including image rejection and selectivity, were typical of receivers today. Interestingly, the SA-GX650's best and worst measurements were of the two characteristics having the most to do with an FM tuner's ability to reject interference on the same frequency. The AM rejection was a mediocre 37 dB, and the capture ratio was a superb 1.0 dB, as rated. The AM frequency response, like that of almost every tuner and receiver we have tested, was very limited at both low and high frequencies.
The tone controls had good characteristics, although the tiny knobs and the lack of clear index markings made it difficult to determine their settings. Particularly for the treble control, we found that turning the knob halfway up or down had an insignificant effect on the response. The loudness control boosted the frequencies below several hundred hertz by about 10 dB at volume settings of -20 dB and below.
The main (left and right front) power amplifiers easily met and surpassed their ratings. Their 125-watt stereo rating is conservative: We measured 165 watts into 8 ohms at the clipping point, and at 125 watts into 8 ohms the distortion remained well below the rated 0.05 percent from 20 Hz to 20 kHz. If the receiver is used with speakers having much less than 8 ohms impedance, however, it should be set for low-impedance operation.
We succeeded in blowing an internal fuse near the clipping point with a 4-ohm load (evidently the electronic protection did not take effect in time). Fortunately, the receiver was not damaged by this abuse and required only a fuse replacement (it is not considered "user replaceable" since that involves removing the cover).
We used the SA-GX650 with very good results in a surround system with two front speakers and two side-mounted ambience speakers. Unlike some considerably more elaborate (and expensive) receivers, the SA-GX650 makes no attempt to simulate a number of acoustic environments. In a normal room, with reasonably good stereo recordings (not specially encoded ones), there was a worthwhile amount of ambience enhancement. We did not use the receiver with Dolby-encoded movies (which presumably would be a major application for it), but the sound with a Dolby Surround-encoded CD clearly demonstrated its suitability for home theater use. And its ease of operation-a quality notably absent in many more elaborate receivers-is a significant bonus. At its moderate price, the SA-GX650 is certainly an excellent value.
