Anyone who thought that the soaring yen would price the Japanese out of the consumer
electronics market has another think coming. When a company like Technics prices
its top-of-the-line Dolby Pro Logic A/V receiver-the SA-GX770---at $499.95
(THX systems go for more), it's clear that the Japanese have a way of coping
with "endaka"--the rising
yen of the 1990s-just as they cleared the "oil shocku" hurdle in
the 1970s.
With Japanese labor costs now exceeding those in the United States and much of Western Europe, the only way to build in Japan and stay competitive is to be vertically integrated and highly automated. Matsushita, Technics' parent company, fills the bill in both respects, as was quite apparent on a press trip I made to their Osaka factory last spring. Compared to what I saw on a visit two years prior, Matsushita has speeded its automatic insertion equipment dramatically and redesigned the guts of its receivers to minimize the number of wiring harnesses so that even final assembly is performed by machines.
Fundamental in Technics' drive for competitiveness, however, is the development of a new series of high-efficiency, two-channel, hybrid power modules that operate in what the company calls Class H+. As you're probably aware, several companies have adopted Class-H output topologies to improve efficiency in the region where audio output stages typically operate when handling music, that is, when they're delivering between 10% and 40% of rated out put. Conventional Class-AB stages operate from fixed supply voltages and are most efficient when operating at maximum rating. At 10% of rated output, they're only about 20% efficient; at 40% of rated output, they're about 50% efficient and generate as much heat as useful power.
The idea behind Class H is to employ two sets of supply voltages ("rails") and switch between them, depending on signal demands. When idling or delivering relatively low output levels, the low-voltage rails are used; as the signal level approaches the limits of the low-voltage supplies, the high-voltage rails take over. With adroitly chosen voltages, the improvement in efficiency can be dramatic, since the amplifier operates from the low-voltage source most of the time an:, to the extent that the amplifier deliver; power close to the maxi mum possible with those supplies, use each of the supply voltages in an efficient manner.
The problem with Class H comes in the transitions between supply rails. If the switchover is abrupt, distortion can be introduced; if it's slow, the system can't track high-frequency signals. Technics claims to have overcome these problems by using "variable amplifier bias" and "frequency dependent control"-the distinguishing features of Class H+. "Variable bias" anticipates what the signal is likely to do and adjusts for it. As the signal approaches the limit of the low-voltage supplies, the high-voltage pair is brought into action and turned on more fully as the signal reaches and exceeds the low-voltage limits, in the expectation that the signal level will continue to rise. Frequency dependent control" keeps the rails at the higher voltage for a short period of time after the signal drops so that, if high frequencies are present, each cycle is not handled independently; instead, the switchover tracks the signal "envelope." Technics has developed a series of hybrid power modules based on this concept. Each handles two channels and contains four output transistors (two per channel), a pair of Class H+ control transistors that govern the supply rails for both channels simultaneously, a protection IC, a driver IC, and assorted other components to make up two complete output stages. The hybrid modules are assembled and tested by automated equipment so that when they reach the final production line, they're sure to work.
The SA-GX770 uses two of the most potent Technics hybrids, and, as A/V receivers go, it certainly doesn't lack for power. In stereo, it carries an FTC rating of 125 watts per channel into 8-ohm loads (0.05% THD from 20 Hz to 20 kHz); in five-channel operation with 8-ohm loads all around, Technics claims 100 watts into each of the three front speakers and 100 watts shared be tween the rear pair. True, the output in the multichannel mode isn't specified in FTC parlance--distortion is specified only at 1 kHz (0.8%)-but that's not unusual among A/V receivers. Thanks to the Class H+ topology, the SA-GX770 is a lot more efficient than previous Technics receivers when handling music. Technics estimates that the SA-GX770 dissipates about 102 watts of heat in normal operation, com pared with 197 watts for a previous model.
Control Layout
Based on features, functions, and price, it seems clear that the Technics SA-GX770 is targeted to those who want a basic, but adequately powered, home theater setup.
It accommodates only two A/V sources ("VCR 1" and "VCR 2") and records on only one of those ("VCR 1"), which is limiting to dyed in-the-wool home theater aficionados. The "VCR 2" inputs appear on both front and back panels (a button above the front set selects which is active); the "VCR 1" inputs are in back.
Video is handled in composite form, via RCA jacks; S-video connections are not provided. Inputs for a CD player, one audio tape deck, and an MM phono cartridge are available, but don't look for fancy gold plated connectors on this unit.
On the output side of the equation are jacks for recording on the audio deck and "VCR 1," a video output for a monitor, left and right subwoofer line outputs, and terminals for two pairs of front speakers, a center speaker, and a rear pair. The center speaker connectors are spring-loaded; the others have manual clamps. Completing the rear panel are a detachable line cord, two switched outlets rated at 80 watts, screw terminals for turntable ground and for 75-ohm FM and single-wire AM antennas, a special jack for the AM loop (included), and a remote-control jack to tie into other Technics equipment. A reasonably quiet cooling fan activates.
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SPECS:
AMP SECTION
FTC Power Rating, Stereo Mode: 125 watts/channel at 0.05% THD, 20 Hz to 20 kHz, both channels driven, 8 ohm loads.
Power Rating, Five-Channel Mode, for 0.8% THD at 1 kHz, 8-Ohm Loads: Front, 100 watts x 2; center, 100 watts; rear, 100 watts.
Low-Frequency Damping Factor: 30 (8 ohms).
Dynamic Headroom: 2 dB (8 ohms).
SMPTE IM: 0.3% (8 ohms).
Frequency Response: Phono, RIAA standard curve, ±0.8 dB; line, 7 Hz to 70 kHz, ±3 dB.
Input Sensitivity/Impedance (IHF):
Phono, 0.4 mV/47 kilohms; line, 27 mV/22 kilohms.
S/N, A-Weighted (IHF, re: 1 Watt):
Phono, 70 dB; line, 75 dB.
Tone-Control Range: Bass, ±10 dB at 50 Hz; treble, ±10 dB at 20 kHz.
Loudness Contour: +9 dB at 50 Hz (volume at -30 dB).
FM TUNER SECTION
Usable Sensitivity: Mono, 11.2 dBf.
50-dB Quieting Sensitivity: Mono, 18.3 dBf; stereo, 38.3 dBf.
Total Harmonic Distortion: Mono, 0.2%; stereo, 0.3%.
Signal-to Noise-Ratio: Mono, 75 dB; stereo, 70 dB.
Frequency Response: 20 Hz to 15 kHz, +1, -2 dB.
Capture Ratio: 1 dB.
Alternate-Channel Selectivity: 65 dB.
11. Rejection: 80 dB.
AM Rejection: 50 dB.
Image Rejection: 45 dB.
Spurious-Response Rejection: 75 dB.
Channel Separation: 40 dB at 1 kHz, 30 dB at 10 kHz.
Carrier Leakage:-35 dB at 19 kHz,-50 dB at 38 kHz.
AM TUNER SECTION
Sensitivity, External Antenna: 20 µV, 330 µV/m.
Alternate-Channel Selectivity: 55 dB.
Image Rejection: 40 dB.
Rejection: 60 dB.
VIDEO SECTION
Output Voltage: 1.0 V, ± 0.1 V, peak to peak.
Maximum Input Voltage: 1.5 V, peak to peak.
GENERAL SPECIFICATIONS
Power Consumption: 300 watts (385 VA).
Power Supply: 120 V a.c., 60 Hz.
Dimensions: 17 in. W x 61/4 in. H x 137/8 in. D (43 cm x 15.8 cm x 35.2 cm).
Weight: 22.2 lbs. (10.1 kg).
Price: $499.95.
Company Address: One Panasonic Way, Secaucus, N.J. 07094.
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Except for an unusually large "Tuning" knob, the control panel is conventional. The "Power" switch is at the lower left, followed by a "Phones" jack, "Speaker A/B" buttons, and source-selector pads ("VCR 1," "VCR 2," "Tape/DCC Monitor," "CD," "Tuner," and "Phono"). At the lower right are "Bass" and "Treble" knobs and the secondary "VCR 2" inputs; above them are a motorized "Volume" control, a small "Balance" knob, and a "Help/Reset" button one of the SA-GX770's really neat features.
How many times has a system seemed to have died when all that's happened is that someone accidentally pressed the tape monitor? If this occurs with the SA-GX770, a tap on "Help" displays a message of what you should do to correct the problem. The receiver monitors itself for common mis takes. For example, if neither front speaker is on when you power up the unit, "Speakers Off' scrolls across the display. Not all problems are handled so easily, but neophytes (and even old-timers) should react positively to this "Help" feature.
Mirroring the "Volume," "Help," and "Balance" controls on the right are those for "Tuning," "Tuning Mode," and "Direct Tuning" on the left. "Tuning Mode" cycles through three possibilities: "Auto," which seeks the next available station; "Manu al," which permits you to tune stations with the "Tuning" knob, and "Lock," which locks in the current station. "Direct Tuning" permits you to enter a specific station frequency with the 10 numeric pads under the main display. These also serve to recall any of the 30 station presets. You can load presets manually or automatically. In the latter case, the first 20 slots are assigned to the FM band and the last 10 to the AM band. Auto presetting is activated by pressing the "Memory" key at the far right of the numeric pads; manual presetting is accomplished by tuning to the desired station and then pressing "Memory" and selecting the desired preset number.
The remaining controls are sandwiched between the numeric pads and the source selectors. On the far left, "Band" chooses the reception band, and "FM Mode" toggles be tween stereo and mono reception.
On the far right is a "Muting/Loudness" key. A momentary press mutes or un-mutes the receiver; pressed and held, the loudness toggles on and off. In the middle are the surround controls. The first pair from the left, "Surround" and "3 Stereo," activate the Dolby Pro Logic decoder in either full Dolby Pro Logic surround or in a three-channel mode that doesn't use rear speakers. A second tap toggles the system off. "Test," "Center Level," and "Rear Level" pads come next and are used to balance the system. "Center Mode" cycles between normal-, wide-, and phantom center operation, and "Delay Time" adjusts rear-channel delay in 5-mS increments from 15 to 30 mS.
The SA-GX770 comes with a 56 key remote control that is compatible with Technics products manufactured since 1985. The remote is preprogrammed with the control codes needed to operate equipment from many other manufacturers.
Measurements
Fig. 1-Amplifier section THD + N vs. frequency.
Fig. 2-THD + N vs. output for loads of 8 ohms (A) and 4 ohms (B).
Fig. 3-Frequency response for phono and CD inputs.
Fig. 4--Action of tone controls, loudness compensation, and subwoofer filter.
Fig. 5--Crosstalk
Fig. 6--Noise spectrum, CD input.
Fig. 7--FM quieting characteristics.
Technics' new hybrid power modules do a nice job. Although the SA-GX770 is rated at "only" 125 watts (21.0 dBW) per channel (8-ohm loads), I measured a clipping point of 170 watts (22.3 dBW) per channel with those loads and 215 watts (23.3 dBW) per channel when terminating with 4 ohms. As shown in Fig. 1, THD + N is safely under Technics' 0.05% spec at rated power across the band. Only the 10-watt curves show an increase in distortion above 7 kHz that can be attributed to Class-H operation. However, as you can see, distortion just touches 0.04% at 20 kHz, so I consider it negligible. At full power, the anomaly disappears, presumably due to the "frequency dependent control" circuit.
Figure 2 displays THD + N as a function of power at three test frequencies. Figure 2A shows the results with 8-ohm loads, Fig. 2B with 4-ohm termination. The 20 kHz curves show a hint of Class-H switching distortion in the region of 6 to 12 watts with 8-ohm loads and in the region of 10 to 20 watts with 4-ohm loads, but it's just a hint. Class H can be much worse than this.
The hybrid modules also do well on bursts. Dynamic power, using the IHF tone burst, clocked in at 230 watts per channel with 8-ohm terminations, for a dynamic headroom of 2.6 dB-well above spec.
With 4-ohm loads, I measured 315 watts per channel from this "125-watt" receiver.
Damping factor (140) was much better than Technics' claim, and output impedance stayed relatively low across the audio band (rising from 55 milliohms at 1 kHz, to 75 milliohms at 5 kHz, 120 milliohms at 10 kHz, and 180 milliohms at 20 kHz).
The SA-GX770 proved more sensitive than spec. From the high-level inputs, it delivered 1 watt from an 18.3-mV source and needed only 0.32 mV (1 kHz) for equivalent output from the MM phono input. Sensitivities for rated output calculate to be 205 and 3.6 mV, respectively.
As shown in Fig. 3, frequency response is quite flat for an amplifier without a tone-defeat switch: +0, -0.5 dB from 20 Hz to 25 kHz (-3 dB at 70 kHz) from the CD input and +0, -0.6 dB from 25 Hz to 20 kHz from the phono.
Input impedances (34 kilohms for CD, 44 kilohms in parallel with 130 pF for MM phono) seemed fine. With standard volume setting, channel balance was perfect from the CD input. The A-weighted noise, although set ting no new standard, was -76.2 dBW (CD input) and -71.5 dBW (MM phono), safely above Technics' claims. When referenced to rated power, A-weighted S/N ratios become 97.2 and 92.5 dB, respectively.
Figure 4 depicts the tone-control range, the loudness contour, and the response of the internal subwoofer crossover. At 50 Hz, the bass provides a range of +10,-10.6 dB; at 10 kHz, the treble can boost 8.7 dB and cut 10.5 dB. Engaging the loudness circuit produces a 9.3-dB boost at 50 Hz. Subwoofer crossover occurs at 110 Hz (-3 dB), with a slope of 12 dB per octave.
Levels at the recording terminals measured 0.27 V from the MM phono input (5 mV at 1 kHz) and 0.51 V when using the FM tuner (100% modulation).
From high-level inputs, the gain was close to unity: 0.475 V out for 0.5 V in. Output impedance at the recording jacks was a bit high, 3.6 kilohms. Keep the cable length reasonably short.
Crosstalk from the CD inputs is better than-50 dB from 30 Hz to 4.5 kHz and -45 dB out to 10 kHz (see Fig. 5). A third-octave spectrum analysis from that input (Fig. 6) is remarkably free of hum components.
The SA-GX770's only weakness as far as amplifier performance is concerned lies with the rather low input-overload mar gins. Input clipping occurred with a 62-mV (1-kHz) signal at the MM phono terminals and with a 3.6-V CD input.
Although the numbers are below those I'd like to see, I don't expect you will en counter any problems in most listening situations. Most CD players output a maxi mum of 2 V, and I expect that only very high-output cartridges are likely to deliver more than 62 mV from a record.
As far as sensitivity goes, the FM tuner in my sample proved disappointing, so I obtained a second unit and made all FM measurements on it. As shown in Fig. 7, 50-dB quieting with mono modulation is attained with a 19.9-dBf input; equivalent quieting in stereo is reached at the 44.0 dBf level. The tuner comes within a whisker of meeting its rated mono S/N ratio (74.6 dB versus the 75-dB spec). In stereo, I measured an S/N of 67.0 dB at the 65-dBf reference level, but, with a stronger input applied, the S/N continues to improve and tops out at just a shade under the 70-dB spec.
In Fig. 8, tuner THD + N versus frequency, there is virtually no difference be tween the mono and stereo curves out to 600 Hz; distortion on both averages just under 0.5%. Above 600 Hz, stereo distortion rises (typical) and mono distortion decreases (atypical). At the 6-kHz bench mark, THD + N is 2.12% in stereo and 0.21% in mono.
Figure 9 shows AM and FM frequency response and FM separation. The FM response is excellent -- +0.0, -0.6 dB from 26 Hz to 15 kHz -- and separation is 30 dB or better from 130 Hz up. The AM response is typical: +0.2, -6 dB from 95 Hz to about 3 kHz.
Capture ratio measured a decent 1.4 dB at 45 dBf, and the tuner exhibited very good selectivity: 8.1 dB from the adjacent channel, 70.5 dB from the al ternate channel. Image rejection was 51.7 dB, and AM rejection was 52.9 dB--both better than spec. The 19 kHz pilot was suppressed by 36.3 dB (the 38-kHz subcarrier by 61.9 dB) at the tape recording output. With Dolby Pro Logic decoding, response is very good at all outputs.
As shown in Fig. 10, front-channel response is essentially identical to that in stereo mode, while center channel response (center-wide mode) is within +0, -0.5 dB from 62 Hz to 20 kHz (-3 dB at 28 Hz).
In the center-normal mode, the low end is down 3 dB at 100 Hz, which is Dolby Labs' recommendation.
Rear-channel response is down 3 dB at 6.6 kHz (again in accordance with Dolby Standards) and at 35 Hz on the low end.
With 8-ohm loads and Dolby Pro Logic decoding, the front channels delivered 115 watts (20.6 dBW) a side at clipping; the center delivered 120 watts (20.8 dBW). Rear-channel clipping occurred (17.8 dBW); this makes sense, since the same output circuit drives both channels and is delivering 120 watts into the pair. The A-weighted noise measured -73.7 dBW in front, -74.0 dBW in the center, and-69.9 dBW in the rear. This yields signal-to noise ratios (referenced to the clip ping points) of 94.3, 94.8, and 87.7 dB, respectively.
Fig. 8-THD + N vs. frequency, FM tuner section.
Fig. 9-FM and AM frequency response and FM-stereo crosstalk.
Fig. 10-Frequency responses, Dolby Pro Logic mode.
Fig. 11-THD + N vs. frequency, Dolby Pro Logic mode.
Figure 11 is a plot of THD + N versus frequency at rated output with Pro Logic decoding. (The rear channels were measured at 50 watts each.) As Pro Logic systems go, the results are excellent-especially in the three front channels, which produced less than 0.1% THD from 38 Hz to 12 kHz. It's normal for the rear-channel distortion to be greater than that in front, and the results I obtained on the SA-GX770 are fine in my book.
Pro Logic channel separation was adequate, close to or better than 30 dB between opposing channels.
Separation between the left front and the rear was best (64.6 dB); separation between the right front and the center was worst (29.8 dB). On average, separation was on the order of 40 dB.
Use and Listening Tests
The Technics SA-GX770 is somewhat of an enigma. It's easy to use, the ergonomics are good, and the "Help" feature may avoid unnecessary calls to the repair shop or re duce time spent looking for "obvious" problems. It sounds fine--I'd even say great, considering the price-and the Pro Logic operation is certainly adequate. I don't know where else you can get this much power for the money-or power that's so sensibly distributed among the channels.
Setting aside the relatively low input clipping points (which are unlikely to cause a problem under average conditions), the major fly in the ointment (as I see it) is the paucity of A/V inputs. In my book, two ain't enough. Not for anyone seriously interested in home theater.
Anyone who wants to use the SA-GX770 for both music and home theater is likely to come up short. If you tie up the two line-level audio inputs with a CD player and tape deck, how do you feed a stereo TV broadcast to the decoder? If you use "VCR 2" to feed stereo from your IV into the receiver, you're down to one VCR or a videodisc player, but not both. To use two VCRs or a VCR and a disc player, you'll have to use the TV tuner in one of the VCRs for reception. That may be adequate for an entry-level product, and entry-level buyers should probably give this receiver serious consideration. It delivers far more than entry-level power and (by and large) far better than entry-level performance at an entry-level price. I guess I'm just chagrined that with so much to offer, the SA GX770 could be far more than an entry level product-if only it had a few more inputs!
-Edward J. Foster
(adapted from: Audio magazine, Jan. 1995)
Also see:
Technics SA-GX910 A/V Receiver (July 1992)
Technics SU-A8 Preamp and SE-A7 Power Amp (May 1982)
Technics SL-P3 Compact Disc Player (Equip. Profile, Aug. 1985)
Technics SL-P8 Compact Disc Player (April 1984)
Technics SL-P1200 Compact Disc Player (Dec. 1987)
Panasonic Hi Fi Discrete 4-Channel System (ad, Feb. 1973)
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