Mitsubishi DA-R15 Stereo Receiver Review

The Mitsubishi DA-R15 is one of that company’s line of four stereo receivers. The DA-R15 is rated to deliver 45 watts per channel to 8-ohm loads from 20 to 20,000 Hz with no more than 0.015 per cent total harmonic distortion. Unlike most receivers, it also carries a 4-ohm rating of 60 watts with no more than 0.05 per cent distortion. The DA-R15 has a digital-synthesis tuner whose frequency is displayed in large (1/2-inch) blue-white digits. Grouped in a “dial window” area on the right half of the panel together with the frequency display are a number of pushbuttons, a large volume knob (marked attenuator), and a horizontal row of five green LEDs that indicate relative signal strength.

At the right of the frequency readout are two flat tuning buttons (marked UP and down) and a red stereo light. Below the attenuator knob are five switches that select wide or narrow i.f. bandwidth, FM or AM reception, high blend for noise reduction on weak stereo signals, tuning mode (auto or manual), and muting/mono. The muting/mono switch is marked for on/auto and off/mono operation. The first (outer) position activates the FM interstation-noise muting and provides automatic switching from mono to stereo when a received stereo signal is strong enough for reasonably good reception. Pressing the button in disables the muting and sets the tuner for mono only. The tuning switch affects the operation of the UP and down buttons; in manual the frequency steps by one increment (200 kHz for FM and 10 kHz for AM) each time the button is pressed. The tuning scans rapidly while the button is held in. With the switch set for auto, the tuner scans in the selected direction until it encounters a signal exceeding the muting threshold. Although the muting system does not operate on the AM band when tuning manually, it is effective when scanning AM as well as FM stations.

Below the frequency display is a row of seven preset buttons and a memory button. To store the frequency of any station in the receiver’s memory, the memory button is pressed and then (within five seconds) one of the preset buttons. Subsequently touching a preset instantly tunes the receiver to its assigned frequency. Each button can be used for one AM and one FM channel for a total of fourteen stored frequencies. When a frequency is tuned, a red light appears in the center of the selected button.

The rest of the operating controls on the Mitsubishi DA-R15 occupy the left half of the panel. They include detented bass and treble tone controls (with a tone defeat button between them), a balance control, and a loudness control that operates independently of the volume-control (attenuator) setting. It has eleven stepped positions, and when it is fully clockwise the frequency response is flat. Rotating it counterclockwise reduces the volume, emphasizing the low and high frequencies relative to the midrange. It is designed to give the best results when the listening volume is first adjusted (with the loudness control at maximum) to the loudest one expects to listen to the system. Then the loudness control alone is used to control the level, preserving the psychoacoustic balance between the midrange and the frequency extremes as the volume is reduced.

Pushbuttons control power, two sets of speaker outputs, the low and high filter, and the stereo/mono mode. There are separate program-selector and record-se-lector knobs that provide independent control of the monitored and recorded program sources. The program-selector positions are marked tape 1, tape 2, tuner, phono, and aux. The record-selector positions, in addition to the last three, include two for dubbing from either of two tape decks to the other and an off setting that disconnects all tape outputs from the signal channel. There is a headphone jack on the front panel but no pilot light, since the tuner’s frequency display is on regardless of the selected program source.

On the rear of the DA-R15 there are insulated spring-loaded connectors for the speaker outputs and a holder for three AA cells that maintain the station memories if power is removed from the receiver. Two of the three a.c. convenience outlets are switched. There are inputs for 75- or 300-ohm FM antennas and an AM wire antenna. Normally the AM terminals are connected to a hinged AM loop antenna, which can be unclipped and oriented for best reception. The wooden cabinet of the DARI 5 is finished in walnut-grain vinyl veneer. The receiver is 18-1/2 inches wide, 17-1/4 inches deep, and 5-3/8 inches high and weighs 25 pounds. Price: $440.

Laboratory Measurements. After the usual preconditioning period, the 1,000-Hz audio output of the Mitsubishi DA-R15 clipped at 60.5 watts per channel into 8-ohm loads. The 4-ohm and 2-ohm clipping power outputs were 81 and 70 watts, respectively. The IHF clipping headroom of the receiver was about 1.3 dB for both 8- and 4-ohm operation. The short-term power output (in the IHF dynamic-power test) was 12.5 watts into 8 ohms and 110 watts into either 4 or 2 ohms. The IHF dynamic headroom was 2.07 dB at 8 ohms and 2.6 dB at 4 ohms. The distortion rose gently from 0.0015 per cent at 1 watt to 0.0036 per cent at 50 watts and 0.024 per cent at 60 watts. The 4-ohm distortion was between 0.002 and 0.007 per cent from 1 to 70 watts, and into 2 ohms it increased from 0.0022 per cent at 1 watt to 0.012 per cent at 50 watts.

When the unit was driving 8-ohm loads at rated power, the distortion was just over 0.002 per cent from about 50 to 1,500 Hz, reaching 0.004 per cent at 20 Hz and 0.01 per cent at 20,000 Hz. At lower power levels the characteristic was similar but the distortion was even lower, measuring under 0.002 per cent over much of the frequency range and reaching 0.01 per cent or slightly less at 20,000 Hz.

The amplifier sensitivity for a 1-watt reference output was 27 millivolts (mV) at the aux input and 0.1 mV at the phono input. The noise level was slightly better than — 80 dB referred to 1 watt through either. The phono preamplifier overloaded at 170 mV at 1,000 Hz and slightly less at the frequency extremes. At 20,000 Hz the overload level was the equivalent of 103 mV at 1,000 Hz, more than adequate for any likely combination of cartridge and record.

The IHF intermodulation distortion was measured with equal-amplitude input tones of 19 and 20 kHz, their combined peak level being equal to that of a 45-watt sine-wave signal. In the outputs, the third-order distortion at 18 kHz was —78 dB referred to 45 watts, and the second-order (1,000-Hz) component was a barely detectable —98 dB. The amplifier was stable with simulated reactive-loudspeaker loads, and its IHF slew factor was 1.5 (slew limiting was visible on the waveform at 30 kHz when the amplifier was driven to rated power). The frequency response at 1-watt output was -3 dB at 165 kHz.

The tone-control response curves were conventional, with the bass-turnover frequency in the 200- to 300-Hz range and the treble curves hinged at 3,000 Hz. The loudness contours boosted both low and high frequencies with a very gradual and progressive action as the setting was reduced, and this prevented the sound from ever becoming undesirably heavy. The low-filter response was down 3 dB at 20 Hz, and the high filter’s — 3-dB point was 7,500 Hz. Its slope was 6 dB per octave in the audio range, although both filters are rated for 12-dB-per-octave slopes. The RIAA phono equalization was perfectly flat from 20,000 Hz down to less than 100 Hz, rising to +1.5 dB at 20 Hz. When measured through the inductance of typical phono cartridges, the high-frequency phono response changed by no more than a barely detectable 0.5 dB.

The FM-tuner section of the DA-R15 (set for wide i.f. bandwidth) had an IHF usable sensitivity of 12 dBf (2.2 microvolts, or μW) in mono, and the stereo sensitivity was set by the switching threshold of 25 dBf (10 mV), at which level the distortion was 1.1 per cent. The 50-dB quieting sensitivity was 12.8 dBf (2.4 mV) in mono and 35 dBf (31 μV) in stereo. With the narrow bandwidth setting, the sensitivities were within a fraction of a decibel of those figures.

The signal-to-noise ratio (S/N) in either the wide or narrow mode was 78 dB in mono and 71 dB in stereo, both representing excellent performance and both very close to the residual levels in our signal generator. The distortion at the wide setting (w) was 0.086 per cent in mono and 0.16 per cent in stereo; at the narrow setting (n) the corresponding readings were 0.13 and 0.066 per cent.

The FM frequency response was ± 1 dB from 30 to 15,000 Hz. The wide-bandwidth channel separation was almost perfectly uniform across the full audio range, measuring between 38 and 40 dB from 40 to 15,000 Hz and 33.5 dB at 30 Hz. With the narrow bandwidth, the separation actually improved at most frequencies, exceeding 55 dB from 300 to 1,700 Hz and falling to a “worst-case” reading of 32 dB at 30 Hz. The FM tuner’s IHF intermodulation distortion was measured by modulating the signal generator with equal amplitudes of 14 and 15 kHz to a 100 per cent modulation level. A spectrum analysis of the audio output (w, mono) showed third-order components at 13 and 16 kHz at 60 dB below the tone levels and a second-order component of 1,000 Hz at —62 dB relative to 100 per cent modulation. In stereo, both the third-order and second-order products were at — 56 dB, and there were the usual low-level spurious signals elsewhere in the audio range. The narrow- and wide-band results were essentially the same.

The capture ratio at 45 dBf (100 μV) was 1.78 dB (w) and 2.5 dB (n), and AM rejection was a very good 69 to 70 dB in either mode. The image rejection was fair at 45 dB. To our surprise, the alternate-channel selectivity was identical at both settings of the bandwidth switch: an excellent 87 dB. Adjacent-channel readings were also good, with slight differences between the modes (7.6 dB for w and 11 dB for n). The muting threshold was 27 dBf (13 μV) in mono and 25 dBf (10 μV) in stereo. The 19-kHz pilot-carrier leakage into the audio output was — 66 dB (w) and —69 dB (n), and the tuner hum level was a very low —78 to —80 dB. The AM tuner frequency response was typical of that found in receivers: — 6 dB at 65 and 3,250 Hz.

Comment. As the test data show, the Mitsubishi DA-R15 is an uncommonly fine receiver in virtually every respect. Ultra-low audio distortion, no longer a rarity, is nonetheless the exception in moderate-price, relatively low-power receivers such as this one. More to the point, the FM-tuner performance of the DA-R15 is, in many respects, comparable to what we have come to expect from the better separate tuners.

For example, the excellent selectivity and low distortion and noise level of this receiver’s tuner set it apart from most comparably priced receivers. On the key specifications we checked, only the image rejection was less than excellent. In most areas, very high image rejection is not a major requirement of an FM tuner, and even in our rather congested (spectrally speaking) area we never experienced any interference.

The wide/narrow bandwidth switch had a negligible effect on selectivity—and, for that matter, on anything else. We chose to leave it on wide and forget about it, although the opposite choice would have been just as valid.

The operating smoothness of the controls, and especially of the preset buttons, was striking. And, as usual with digitally tuned receivers, there was no trace of unwanted noise during tuning. The use of a small plastic-cased loop antenna for AM reception (instead of the usual ferrite rod, which is very likely to pick up noise and hum) paid off in unusually quiet AM reception. The AM “fidelity” was, perhaps, no higher than that of many other tuners, but it was far more listenable than most. In the audio section, we must mention the very fine loudness-control system, one of the few really useful ones we have used, and the equally desirable recording-program selector. Overall, the Mitsubishi DA-R15 left us with a very positive impression of a thoroughly designed, well-built, smooth-sounding receiver at a very modest price. It looks as good as it sounds, and it matches both of those qualities with its ease of handling—a rare combination of characteristics.

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