Sony TA-E77ESD Preamplifier Review

In general, audio products claimed to be “digital” use conventional analog designs whose characteristics make them suitable for use with digital sound sources such as compact discs. With the TA-E77ESD stereo control amplifier, however, Sony has taken a step toward the goal of true digital compatibility.

All of Sony’s high-end ES series components employ premium-grade electronic parts and materials, as well as exceptionally rugged mechanical construction, to achieve the highest sound quality. In addition, the TA-E77ESD preamplifier contains built-in digital-to-analog (d/a) converters that can process the digital output of a CD player or DAT (digital audio tape) deck. In this sense, it is closer to being a digital component than products that accept only analog signal inputs.

The TA-E77ESD is equipped to control video sources along with a full complement of audio components. Its versatility is demonstrated by the overall connection diagram in its instruction manual. Two audio cassette decks, a CD player with analog outputs, a tuner, and a turntable can be connected to its analog audio inputs, and it also has an unassigned high-level auxiliary input. Two VCR’s (including stereo audio channels, if provided) can be connected to its video input/ output jacks, and a videodisc player can be connected to the third video input; other jacks carry separate chrominance and luminance signals to an external monitor.

There are two digital inputs for CD players having digital signal outputs and a set of digital input/output jacks for a DAT recorder. A separate pair of analog outputs is provided for the dat deck’s analog inputs, since CD’s cannot be dubbed in digital form. Finally, an adaptor loop permits insertion of a graphic equalizer or other signal processor into the signal path. There are two sets of main audio outputs, and all the audio jacks are gold plated. The two AC outlets, one of them switched, are each rated to handle up to 400 watts.

The front panel of the Sony TA-E77ESD contains a number of legibly marked, soft-touch pushbuttons that select the input source, mute the signal level by 20 dB, insert an external processor through the adaptor inputs, and bypass the tone-control, filter, and balance-control circuits (SOURCE direct). Bright red led indicators in the buttons show their operating status. Other buttons activate a subsonic filter, select mono or stereo operation, and select the turnover frequencies of the bass and treble tone controls (respectively, 200 or 400 Hz and 3,000 or 6,000 Hz). Front-panel indicators show the sampling frequency of a digital source (32, 44.1, or 48 kHz). Next to the power switch is the sensor window for the supplied wireless remote control, which can also be used to switch the power on or off.

The large attenuator (volume-control) knob, like the input-selector buttons, contains a red led that serves as an index marker. The smaller tone-control knobs have eleven indexed settings; the center position is the “off” setting. The balance knob is also center-detented. Two knobs can select any of the ten input sources for recording on one of the audio tape decks independently of the listening selection. Another knob switches the termination and gain of the phono input for a moving-magnet (mm) or moving-coil (mc) cartridge; the MC input offers a choice of either 30 or 400 ohms resistance. An output knob connects the preamplifier’s output either to the main output jacks in the rear or to the front-panel headphone jack.

The acoustically inert chassis of the TA-E77ESD (which Sony calls the “G-chassis” after the Rock of Gibraltar) is molded from a glass-fiber-reinforced resin that results in a nonconductive, nonmagnetic, and highly rigid structure virtually immune to both internal and external vibrations. The entire unit is supported on large feet that appear to have some vibration-isolation properties. The separately encased power transformer is unusually large and heavy for a preamplifier.

The TA-E77ESD’s audio and video signal circuits are completely isolated, and signal switching is done by high-grade, shielded relays instead of the usual semiconductor circuits. The digital portion is sealed in a copper chassis to prevent spurious-noise leakage into the analog stages. Separate 16-bit d/a converters, with quadruple oversampling at 176.4 kHz, are used for each stereo channel.

The Sony TA-E77ESD is a full-size and rather heavy component. With its wood side plates attached, it is 18-3/8 inches wide, 13-1/8 inches deep, and 5 inches high. It weighs 29 pounds (the rugged steel top plate accounts for about 4-1/2 pounds of the total). The models sold in the United States and Canada are supplied with a programmable remote control designed to control most Sony audio and video components. It can also “memorize” the functions of other infrared wireless remote controls, enabling it to control an entire system even if not all the components are made by Sony. Price: $1,100.

Lab Tests

Driving an EIA standard load of 10,000 ohms in parallel with a 1,000-picofarad (pF) capacitance at 1,000 Hz, the Sony TA-E77ESD’s output clipped at a very high 11 volts (its rated output is 1.5 volts, enough to drive almost any power amplifier up to or near its maximum output). The total harmonic distortion was between 0.0021 and 0.0028 percent from 0.1 to 3 volts output and only 0.013 percent at 10 volts, just before clipping occurred.

At a 1.5-volt level the distortion varied only slightly over the audio frequency range, measuring about 0.003 percent from 20 to 5,000 Hz and a maximum of 0.0046 percent at 20,000 Hz. At lower output levels the readings were slightly higher because of the greater proportional contribution of the preamplifier’s noise content.

Overall, however, the noise was very low indeed. Relative to a 0.5-volt output, the A-weighted noise level was — 89 dB through the high-level AUX input, —84 dB through the mm phono input, and — 75 dB through the MC phono input at its 30-ohm setting (maximum gain). The respective sensitivities at these inputs, for a 0.5-volt output, were 46, 0.7, and 0.045 mv. The mm phono-input overload ranged from 142 to 148 mv across the audio band, and for the MC input (30 ohms) it measured between 8.5 and 9.5 mv. The mm phono-input termination was 46,000 ohms in parallel with a 260-pF capacitance. The crosstalk between the inputs (from AUX to phono mm) was unmeasurable at 1,000 Hz (below —110 dB), — 86 dB at 10,000 Hz, and — 78 dB at 20,000 Hz.

The RIAA phono equalization was flat within ±0.05 dB from 100 to 20,000 Hz, falling off slightly at low frequencies to —0.35 dB at 20 Hz. Through the AUX input, the response was as ruler-flat as we could measure, varying less than 0.01 dB overall from 20 to 20,000 Hz. The subsonic filter, rated to have a 6-dB-per-octave slope below 15 Hz, reduced the output by 1 dB at 30 Hz and 2 dB at 20 Hz. The tone-control turnover frequencies were approximately as marked, with a maximum control range of +8, —6 dB at 20 Hz and ± 10 dB at 20,000 Hz with the 400- and 3,000-hz turnover settings.

To test the performance of the d/a converters of the TA-E77ESD, we drove its digital input from CD players equipped with digital outputs. The first digital source was the Sansui CD-X901. Its inherent response is very flat, but through the digital input of the Sony preamplifier there was an obvious, and very audible, loss of high frequencies. The output dropped above 1,000 Hz to — 6 dB at 9,000 Hz.

To establish the cause of this problem, we repeated the test with a Sony CDP-705ESD and a Yamaha CDX-1100. The results with these players were consistent with each other and showed that the response of the right channel of the TA-E77ESD was flat within ±0.1 dB from 20 to 20,000 Hz, but the left-channel output had a slight high-frequency rise, amounting to about 0.5 dB at 20,000 Hz, and it was also about 0.5 dB greater overall than that of the right channel.

According to Sony, its products are designed to conform to the digital interface standards established jointly by Sony and Philips, the creators of the compact disc format. Although most other manufacturers follow the same standards, some products may deviate from them in ways that do not affect their own performance but can make them incompatible with other digital products that may have been designed using different standards.

Comments

The Sony TA-E77ESD provides clear evidence of how narrow the gap is between good analog performance and the nearly perfect characteristics we expect from digital components. In all important parameters, such as crosstalk, noise, distortion, and response flatness, this preamplifier yielded measurement data that would be acceptable in a digital audio source component such as a CD player or dat deck. Although the TA-E77ESD is not unique in that respect, there are very few other preamplifiers that could match it in a one-on-one comparison. And with the inclusion of its d/a circuits, it begins to take on some of the aspects of a fully digital audio component.

Some other audio amplifiers contain d/a converters, and there may well be a trend toward including them, at least in the upper price brackets. I wonder, however, just what practical advantages result from keeping signals in digital form until they reach the amplifier section. While frequency response, noise, distortion, and crosstalk can all be affected to some degree by interaction between analog circuits, these effects are usually audibly insignificant, making any sonic improvement resulting from digital signal connections questionable. In fact, in our tests both the Sony and Yamaha CD players delivered “better” performance from their own analog outputs than the TA-E77ESD could produce from their digital outputs. Although the differences were sonically insignificant, they definitely did not favor the bypassing of the CD players’ analog sections. Finally, let’s not forget the possibility of digital incompatibility that our experience disclosed.

Putting these questions aside, we must say that the TA-E77ESD is an impressive piece of equipment. It fairly radiates smoothness and precision in its operation and listening qualities. Especially for anyone with a complete audio/video system, it would be hard to find another control center with the capabilities of this one—few of us have as many as ten or twelve signal sources in our music systems! Also, the convenience of a single system controller is substantial.

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