Toshiba SA-R3 Stereo Receiver Review

The Toshiba SA-R3 stereo receiver combines a digital-synthesis AM/FM tuner, a preamplifier with CX decoding in its phono section, and a power amplifier rated to deliver 40 watts per channel to 8-ohm loads from 20 to 20,000 Hz with no more than 0.04 per cent total harmonic distortion. Most of its controls are light-touch pushbuttons, knobs being used only for the tone and balance controls and a vertical slider for the volume control.

Lights show the selected input (AM, FM, phono, aux/video, and either tape or source programs). Like most digitally tuned receivers, the SA-R3’s FM-mode selector disables the muting in its mono position. There is also the usual choice of manual or auto tuning modes, respectively advancing one channel at a time or searching for the next receivable signal. Each of the five station-memory buttons is usable for an AM and an FM channel. Separate buttons connect the two sets of speaker outputs. They are wired in series; pressing both buttons with only one set of speakers connected will silence the receiver.

The CX-decoder circuits are switched in by a button on the front panel. With CX-encoded records this provides 15 to 20 dB of noise reduction and an overall dynamic range (depending on the record) of as much as 80 dB. Conventional LP records should be played with the CX system turned off. The CX decoder is level-sensitive, and the receiver must be calibrated to the output level of the system’s phono cartridge using two screwdriver-adjusted controls on the rear panel. A flexible test record supplied with the receiver has 1,000-Hz tones recorded separately for the two channels at the CX reference groove velocity of 3.54 cm per second. While playing the record, the CX level control for each channel is set so that a nearby LED glows. Once made, this adjustment need not be repeated unless the cartridge is changed.

Also on the rear apron of the SA-R3 is a hinged, removable AM loop antenna, which can be located a short distance from the receiver and oriented for best reception. The receiver is finished in satin silver with a black-tinted display window containing the frequency readout, signal-strength lights, and other indicators. It is 16-1/2 inches wide, 13-1/4 inches deep, and 4-1/4 inches high, and it weighs 15 pounds. Price: $400.

Laboratory Measurements

Although the Toshiba SA-R3 is a rather lightweight receiver, even for its modest power rating, it did not become unduly warm during our preconditioning or full-power tests. With both channels driving 8-ohm loads at 1,000 Hz, the outputs clipped at 52.5 watts per channel, for a clipping headroom of 1.18 dB. With 4-ohm loads, the clipping power was 64 watts, although an internal d.c. fuse blew when we drove both channels simultaneously to clipping with 4- and 2-ohm loads. The 2-ohm continuous output was limited by the fuses to only a few watts, and we did not attempt to measure it. The pulsed waveform of the dynamic-headroom test enabled us to drive the amplifier to 63.2, 80, and 104 watts into loads of 8, 4, and 2 ohms, respectively, giving an 8-ohm dynamic headroom of 2 dB.

The distortion of the SA-R3’s amplifier section was well within its ratings under any conditions short of clipping. At 1,000 Hz into 8 ohms, it was between 0.0032 and 0.007 per cent for power outputs between 1 and 50 watts. With 4-ohm loads, the distortion was still only 0.0056 to 0.008 per cent from 1 to 60 watts. At the rated 40 watts into 8 ohms, the distortion was typically under 0.01 per cent from 30 to 15,000 Hz, reaching 0.02 per cent at 20,000 Hz and 0.03 per cent at 20 Hz. At half power and less, the distortion was much the same, typically well below 0.01 per cent and never exceeding 0.02 per cent from 20 to 20,000 Hz. The IHF intermodulation distortion, using inputs of 18 and 19 kHz, was a good — 82 dB for the second-order component at 1.000 Hz but a relatively high —52 dB for the third-order products at 17,000 and 20.000 Hz. There is no reason to expect that the third-order distortion will be audible (it was not to us). The amplifier was stable with reactive simulated-speaker loads and had a slew factor of 2.5 (with a “rated power” sine-wave drive level, the output waveform became triangular at about 50 kHz).

A reference output of 1 watt required an aux input level of 66 millivolts (mV) or a phono input level of 0.3 mV. The corresponding A-weighted noise levels were unmeasurable for the aux input (less than — 90 dB) and a very low —85.5 dB for phono. The phono preamplifier overloaded at very safe levels, from 150 to 170 mV depending on the frequency. When measuring the phono-input impedance, we were surprised to find an extremely low capacitance of 13 picofarads combined with a resistance of 100,000 ohms, not the standard 47,000 ohms. The CX circuits could be calibrated for inputs between 1.15 and 35 mV, a range that encompasses every moving-magnet cartridge made as well as some high-output moving-coil units. The precise CX-level indicator LED lit up within a range of only ± 4 per cent around the correct voltage.

The tone controls had typical Baxandall characteristics, with a sliding bass-turnover frequency and a hinged treble-turnover frequency. The loudness compensation provided only a modest bass boost (a maximum of about 6 dB) and had a shelved response that was flat below 200 Hz and above 1,000 Hz, with a small level difference between the two sections. The subsonic (16-Hz) filter had a 6-dB-per-octave slope and affected the response as high as 200 Hz but reduced it by only 3 dB at 30 Hz. The phono equalization was within ±0.5 dB of the ideal RIAA characteristic from 20 to 20.000 Hz, and it was not affected significantly by phono-cartridge inductance.

The FM tuner section of the Toshiba SA-R3 had a usable sensitivity of 13.2 dBf (2.5 microvolts, or μV) in mono, and the mono and stereo 50-dB quieting sensitivities were 15.8 dBf (3.4 μV) and 37.7 dBf (42 μV), respectively. The stereo (and muting) threshold was 22.7 dB (7.5 μV). The signal-strength indicator lights were usefully spaced, with the first light coming on at the muting threshold, the next three at approximately 6-dB intervals, and the highest (the fifth) at 54.1 dBf (280 μV).

The FM distortion at a 65-dBf (1,000-μV) input was 0.16 per cent in mono and 0.25 per cent in stereo, with noise levels of — 77 and —70 dB, respectively. The IHF intermodulation distortion, with modulating frequencies of 14 and 15 kHz, was —62 dB for the second-order (1,000-Hz) component in mono and —68 dB in stereo. The third-order (13- and 16-kHz) distortion components were —67 dB in mono and — 72 dB in stereo. The tuner’s capture ratio was 1.2 dB at 65 dBf input, and the AM rejection was 57 dB at 45 dBf (100 μV). The image rejection was 62 dB. Alternate-channel and adjacent-channel selectivity readings were 66 and 7.8 dB, respectively. The 19-kHz pilot-carrier leakage was a low — 73 dB, and the power-line hum was —65 dB (almost all at 60 Hz).

The stereo FM frequency response was fiat within +0.8, —1.5 dB from 30 to 15.000 Hz. The channel separation was between 42.5 and 45 dB from 30 to 1,500 Hz, falling smoothly to 30.5 dB at 15,000 Hz. The AM-tuner frequency response was down 6 dB at 36 and 2,800 Hz.

Comment

The Toshiba SA-R3 proved itself to be a thoroughly competent receiver. Its FM-tuner measurements were all quite good, and for the most part the same could be said for the audio amplifier section. The unusually high phono-cartridge load resistance may have an audible effect on a cartridge’s response—some high-inductance cartridges that depend on the usual 47,000-ohm termination to obtain their rated response may show high-end peaks—but lower-inductance types should not be affected significantly. In our listening tests, we never heard any coloration that could be attributed to this factor.

The power output of this receiver should be adequate for the great majority of home installations. Like most Japanese receivers, the SA-R3 was not meant to drive load impedances much lower than 4 ohms, and its protective system will not permit such operation, at least at fairly high levels. We never got a chance to find out if it has electronic current limiting, but the power-supply fuses perform that function very nicely without undesirable side effects (and the inconvenience of removing the cover to replace them discourages unnecessary pushing of the amplifier past its limits). It was gratifying to find that the amplifier can deliver a high short-term peak output, even to 2-ohm loads, without apparent distress, and its sound is not likely to suffer from such operation. The series connection of the second set of speakers makes it almost impossible to present the amplifier with too low an impedance accidentally.

On the whole, the compact SA-R3 is attractive and simple to operate. Its built-in CX decoder works well and takes only moments to calibrate. The decoded CX records we heard through it were all that could have been desired, with virtually inaudible noise, clean sound, and no objectionable expansion artifacts.

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