Sony TA-F555ES Integrated Amplifier Review

Sony’s TA-F555ES integrated amplifier features what its manufacturer callsan “Audio Current Transfer” system (ACT). A front-panel inscription further identifies ACT as “a current drive amplifier system that has electrically separated the four amplifier sections for total elimination of mutual interference.” Elsewhere we are told that this involves the use of completely separate power supplies for each of the preamplifier and power-amplifier sections. According to Sony, the TA-F555ES is intended to meet the special demands imposed by digital Compact Discs, and to this end the amplifier is said to have 100 dB of channel separation at 100 Hz, a 120-dB dynamic range, and a “linear gain control.” The TA-F555ES is rated to deliver 100 watts per channel into 8-ohm loads from 20 to 20,000 Hz with no more than 0.004 per cent total harmonic distortion and into 4-ohm loads with no more than 0.01 per cent distortion. Its circuits are direct-coupled from the high-level inputs to the speaker outputs, and protective circuits prevent damage to either the amplifier or the speakers from a malfunction or most forms of careless operation. A rocker switch in the rear selects operating modes for loads from 8 to 16 ohms or from 4 to 6 ohms, the latter for use with low-impedance speakers 'or pairs of speakers wired in parallel.

The inputs (phono, two tape decks, and three other high-level sources, including one identified as “CD”) are selected by pushbuttons that have illuminated indicators above them. Red lights below the buttons show which source is being channeled to the tape-recorder outputs. Along the lower edge of the front panel are the usual tone and balance controls, the speaker selector, and a headphone jack. There is also a small knob that selects the recording output, including a tape-copy connection from deck 1 to deck 2. A cartridge load switch selects either moving-magnet (MM) or moving-coil (MC) amplification, with a choice of either 100 or 330 picofarads of capacitance for an MM cartridge and either 30 or 400 ohms of input resistance for an MC cartridge.

The tone controls can be bypassed with a nearby button. Other buttons select a fixed bass boost and a subsonic filter function. The TA-F555ES does not have loudness compensation. Its large volume knob contains a light that serves as an index line, changing from green to red when the protective system has silenced the amplifier (shutting off the power for a few seconds allows the circuits to reset). The rear apron contains heavy-duty speaker-output binding posts and four a.c. sockets (two of them switched) as well as the speaker impedance switch and the signal jacks (the phono jacks are gold plated).

The all-black Sony TA-F555ES is 17 inches wide, 13-3/4 inches deep, and 5-1/8 inches high, and it weighs about 30 pounds. Price: $600.

Laboratory Measurements

Our test sample of the Sony TA-F555ES (an early production unit) was supplied without an instruction manual or schematic. Curious about its four “separate” power supplies, we removed the cover and found one power transformer (granted, a husky one) and the usual minimum of two filter capacitors. The TA-F555ES seems to have one power supply, and the isolation implied in the spec sheet must come from individual voltage regulators supplying each section.

The one-hour preconditioning at one-third power made the top of the case quite hot, but it never became unduly warm in normal use. Using the 8- to 16-ohm setting of the speaker impedance switch, we measured a clipping-power output at 1,000 Hz of 119 watts per channel into 8 ohms. The protective circuit shut down the amplifier at 169 watts with 4-ohm loads and at 36 watts when we attempted to drive 2-ohm loads. The dynamic power output was 150 watts into 8 ohms, 258 watts into 4 ohms, and 142 watts into 2 ohms. With this setting of the speaker impedance switch, the amplifier’s clipping headroom was 0.76 dB into 8 ohms and 2.28 dB into 4 ohms. The corresponding dynamic-headroom measurements were 1.76 and 4.12 dB, the latter being the highest we have yet measured from an amplifier. We repeated these measurements using the 4- to 6-ohm setting of the speaker impedance switch. The outputs were generally lower; clipping occurred at 84.5 and 124 watts for 8- and 4-ohm loads, and the amplifier shut down at 40.5 watts into 2 ohms. The dynamic output was also lower: 94.4 watts into 8 ohms, 158 watts into 4 ohms, and shut-down at 123 watts into 2 ohms. All other measurements were made using the 8- to 16-ohm setting.

The distortion in the TA-F555ES’s output was extremely low at all power levels up to the clipping point and over the full audiofrequency range. At 1,000 Hz, the distortion was from 0.0005 to 0.0014 per cent from 1 to 110 watts with 8-ohm loads and from 0.0016 to 0.0025 per cent over the 1-to 160-watt range with 4-ohm loads. With 8-ohm loads at the rated 100 watts output and also at power outputs of 50 and 10 watts, the distortion was well under 0.002 per cent over most of the 20- to 20,000-Hz range, reaching its maximum of 0.003 per cent only at 20,000 Hz. The amplifier’s outstanding high-frequency linearity was demonstrated by its IHF intermodulation distortion with input signals of 18 and 19 kHz. At 100 watts output, the second-order distortion reading at 1,000 Hz was the same as our test instrument’s residual level of — 97 dB, and the third-order components at 17 and 20 kHz were at —93 dB.

The TA-F555ES had a very high sensitivity on all inputs. The reference output of 1 watt required only 15 millivolts (mV) at the high-level inputs, 0.21 mV at the MM phono input, and 9.3 microvolts at the MC phono input. The А-weighted noise level was unmeasurable through the high-level input (lower than —90 dB referred to 1 watt); for phono (MM) it was —86 dB, and for phono (MC) it was —81 dB. Out of curiosity, since this spec is of little or no importance in a home music system, we also checked the channel separation using the aux input and terminating the undriven input with 1,000 ohms. Sony’s claim of 100 dB at 100 Hz was met (we measured 102 dB). At 1.000 Hz the separation was 88 dB, and at 20.000 Hz it was still a very good 67 dB.

The MM phono input overloaded at inputs of 150 to 160 mV over the 20- to 20,000-Hz range. The phono-input impedance was as specified, 47,000 ohms in parallel with either 100 or 330 picofarads depending on the setting of the capacitance switch. The phono equalization was within 0.5 dB of the RIAA characteristic from 100 to 20,000 Hz, rising slightly in the low bass to +2.5 dB at 20 Hz. It was not affected by cartridge inductance.

The tone controls had a rather moderate effect, with a maximum bass boost or cut of 7 to 8 dB and a turnover frequency of about 500 Hz. The treble curves were hinged at 6.000 to 7,000 Hz, with a maximum range of 7 to 8 dB at 20,000 Hz. Strangely, we found that setting both tone controls to their mid-boost or mid-cut positions produced an almost perfectly flat response, merely varying the overall level by about 2 or 3 dB. Pressing the bass boost button gave a gentle rise in output below about 500 Hz, with a maximum of about 3.5 dB between 20 and 100 Hz. The subsonic filter reduced the response by about 2.5 dB at 20 Hz. We could not determine its cutoff slope below that frequency.

Comment

There can be no doubt that the Sony TA-F555ES is a truly exceptional amplifier. Its low and rather uniform distortion is commendable, even if it is many orders of magnitude below any threshold of audibility. Rather more impressive (to us) was the unit’s fantastically low noise level, which was considerably lower than we have ever before measured (or heard) from an integrated amplifier. More convincing than mere numbers was the acid test of turning up the amplifier gain to maximum with a cartridge connected to the MM phono inputs and using speakers 6 to 8 dB more sensitive than usual. We had to come within a couple of feet of the speakers to hear the faint hiss that was the only output of the TA-F555ES. It would have been quite impossible to play a record at that high a volume setting with the cartridge we were using; the volume control had to be turned below its middle setting before we could even tolerate the sound level.

Everything else about the amplifier worked with total smoothness and silence, from the almost viscous feel of the volume-control knob to the operation of the various buttons and switches. We can confirm that the amplifier’s protection circuits make it virtually impossible to damage, since they shut it down at the first hint of an overload or other abuse.

Sony makes a point of the special suitability of the TA-F555ES for playing digital audio discs with their tremendous dynamic range and negligible noise content. We can only agree. Although this is not a super-power amplifier by any means, its dynamic headroom may well be the largest of any now on the market, and this factor is especially important for handling the peaks that are inherent in live music and digital discs but are almost never present in an analog record or tape. Similarly, one might argue that the overall signal-to-noise performance of this amplifier represents overkill for analog program sources, but that is hardly the case with properly recorded digital sources. The Sony TA-F555ES certainly has what it takes to do justice to this sonically promising technology.

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