Technics SA-GX790 AV-receiver
As you might expect from a model standing second-from-the-top of the Technics receiver lineup, the SA-GX790 is blessed with many impressive features and ratings. Perhaps the most impressive is the specification for amplifier power, something you can never have too much of: 120 watts per channel in two-channel stereo operation (with no more than 0.05 percent distortion) and 100 watts each for the three front channels and a pair of surround speakers in Dolby Pro Logic operation.
Although the Pro Logic power specs are pegged to a distortion level of 0.8 percent, they're still impressive. And it's most unusual for an A/V receiver to have equal power ratings for all channels in surround operation (a theoretically desirable characteristic, even if it's seldom really necessary). There is, however, a little fudging going on since the surround speakers are actually driven in series by a single amplifier channel (which means both speakers must be hooked up in order for either one to operate). Assuming that the surrounds are identical, the surround-channel power will divide equally into the two speakers, so on a five-channel basis the SA-GX790's rating would be a still-ample 50 watts each to the surround speakers, which is only 3 dB less than 100 watts per speaker.
But however it is rated, this receiver is more than simply a powerhouse. It also has a well-chosen array of stereo and home theater features. The tuner section, for example, will memorize thirty station presets in any combination of AM and FM frequencies. There are four sound-processing modes in addition to Dolby Pro Logic, and the Pro Logic decoder itself has a Theater mode that the receiver's manual says "spreads out the sound as actually happens at the theater."
Inputs and switching are provided for two VCR's, a laserdisc player, a CD player, one audio-only tape deck, and a moving-magnet phono cartridge. There is one video-monitor output. One of the VCR inputs can be switched between rear- and front-panel connectors, the latter being convenient for temporary hookup of a camcorder.
The left side of the rear panel (as viewed from the back) has a thumbscrew 75-ohm connection for the supplied single-wire FM antenna. A special connector is provided for the supplied AM loop antenna as well as a thumbscrew for a long-wire AM antenna. To the right of these connections are the line-level audio jacks in vertical array. The video connections - all phono jacks for composite-video - are next but, confusingly, they are not directly adjacent to their corresponding audio connections. Read the labeling for this portion of the rear panel very carefully. The speaker connections, in the middle of the panel, are all snap clips best used for stripped wire ends. Next to the speaker connectors is a pair of phono-jack line-level subwoofer outputs. There are two switched AC convenience outlets.
The infrared remote control comes preprogrammed to operate many other Technics and Panasonic components. It also carries the operating codes for TV's, VCR's, and laserdisc players from other manufacturers. The receiver-only buttons are scattered over the face of the handset, with little differentiation in size, shape, spacing, or feel and none whatsoever in color. Still, the light coloration behind the surround-decoder buttons makes them highly visible in a dark room, a nice touch on an otherwise only serviceable remote.
The manual is not quite as usable, since it confusingly covers five receiver models at the same time and must be supplemented with multipage auxiliary publications detailing the use of the remote and the contents of the on-screen display. That display, by the way, can be too much of a good thing sometimes, since you can't keep it from turning on and its contents are mostly redundant with the receiver's front-panel display.
Lab measurements showed that the SA-GX790 follows in the tradition of other Technics receivers we've tested recently: average overall FM and Dolby Pro Logic performance combined with distinctly above-average power-amplifier characteristics. The only anomalous result in the FM tests was the high reading for total harmonic distortion plus noise (THD+N) in stereo, which mostly reflects the tuner's rather high pilot-carrier leakage; true audio-range distortion is probably much lower. The AM frequency response was abominable, as has been the case with essentially every receiver and tuner that Stereo Review has tested in recent years.
Measured Dolby Pro Logic performance was fine except for the surround- and center-channel noise levels, which could use considerable improvement (especially the latter). The high noise also worsened the surround-channel distortion figure, since it is a THD+N measurement. In our listening tests the noise, which was present only during operation of the surround modes, was sometimes distractingly audible when there was little or no signal, depending on the volume setting.
It is in its ample power reserves that the SA-GX790 really scores high. Especially impressive are the stereomode figures for clipping power and dynamic power into 4-ohm loads, both of which exceed what we measured for Technics' first Home THX receiver (the SA-TX1000). And given the high outputs available in surround operation, the SA-GX790 will have enough oomph for the most outrageous movie sound effects in any reasonably sized room, as well as for stereo music recordings with wide dynamic range.
There was one blot on the amplifier section's performance, however. The frequency response of the front left and right channels flattened out only when the receiver's bass control was turned down from its center detent to approximately the 11 o'clock position. (This type of error seems so widespread now among A/V receivers as to be almost standard practice.) The deviation, a broad hump starting below 200 Hz that reached about +1 dB at 40 Hz (relative to the level at 1 kHz), was present in both two-channel stereo and surround-sound modes. The SA-GX790 is therefore best auditioned in the store with its bass control turned down slightly, and we used that setting for our listening tests.
The separate subwoofer output was very handy, not least because the SA-GX790 supplies it at two jacks even though it is a mono signal. That eliminates the need for a Y-connector to feed both input channels of a subwoofer crossover, a practice recommended to reduce the possibility of picking up interference through an unterminated subwoofer input. On the down side, the subwoofer outputs remain on even when all of the main speaker outputs are turned off and a headphone is plugged in.
The subwoofer outputs are fed from a low-pass crossover filter that rolled off at 12 dB per octave above 100 Hz, which can be a benefit or a drawback depending on your circumstances. It will definitely be an obstacle if your subwoofer needs to operate up to a higher frequency. In that case you should forget the receiver's dedicated outputs and hook up the subwoofer via speaker-level connections to the main front left and right outputs. Even if your subwoofer requires a lower crossover frequency (say, 80 Hz) and has its own crossover, the receiver's crossover filter characteristics will still interact with those of the subwoofer's. That can roll off the response excessively at the desired crossover frequency, which may prove impossible to counteract with the subwoofer's own controls. Technics probably would have been better off taking the easy (and cheaper) way out by supplying an unfiltered, wideband mono (or, better, stereo) signal at the SA-GX790's subwoofer outputs.
Measurements of the outputs produced by the receiver's music-enhance-ment modes showed that they covered just about every possible variation of what can be done with a single-channel delay line (in this case, the same one used to supply surround-channel delay in Dolby Pro Logic). Depending on the mode selected, the center speaker may or may not be activated and the surround and front left and right speakers may or may not receive a single simulated reflection (derived from either the sum or difference of the two input channels) at the selected delay interval. The receiver makes no attempt at DSP-type simulation of multiple spaced ambient reflections or of the densely packed reflections characteristic of reverberation.
But sometimes less is more. The system Technics has provided has the important advantage of being very easy to use. Select a mode, maybe select a delay interval, maybe adjust the surround-channel level, and that's it. The results, as usual for simple music-processing systems, depend greatly on the sonic characteristics of the original recording. And, again as usual, feel free both to make adjustments and to ignore the names of the various modes. The mode that may be most suitable for enhancing the recording at hand may not be the one whose name seems most applicable.
Our main reservation about the various surround modes, both music- and movie-oriented, was the higher-than-average noise level in the center and surround channels. In every other respect, however, the sound was just fine once the bass control was adjusted properly. Indeed, you could make a very strong case for considering the SA-GX790 primarily as a good, exceptionally high-power stereo receiver, especially if you aren't ready to get into home theater or if you will use its surround capabilities only occasionally. You get a lot of muscle for your money with this receiver. And its relative simplicity makes it easier to operate than many of its competitors, which most people will find a significant benefit.
