Marantz SR 8100 DC Stereo Receiver Review

The Marantz SR 8100 DC Computune receiver combines a digital-synthesis AM/FM tuner with a direct-coupled amplifier rated to deliver its output into 4-ohm loads between 20 and 20,000 Hz at less than 0.06 per cent total harmonic distortion. It is the first receiver we can recall seeing whose primary power rating is based on 4-ohm loads, but it also carries an 8-ohm rating of 75 watts with 0.03 per cent distortion. The tuner section has pushbutton selection of manual or automatic tuning, as well as eight preset channels for each of the AM and FM bands. The tuned frequency is displayed on the front panel by highly visible blue-green ^-inch-high numerals. The SR 8100 DC also has a built-in 24-hour digital clock that displays the time whenever the receiver is turned off or when the clock/frequency display button is pressed.

The clock system also provides several timer functions that can switch the receiver (and a rear a.c. convenience outlet) on and olf at preset times. The timer functions include ONCE ON/OFF and DAILY ON/OFF modes as well as a sleep mode that takes priority over the others and shuts off the receiver after a selected time interval regardless of the off times set by the other timer modes. The internal memories and the clock and timer settings are preserved in the event of a power interruption by four AA cells (without a.c. power, however, the clock display is not operative).

On the front panel (which, like the entire exterior of the receiver, is finished in satin gold), there are a number of pushbutton controls. One group of eleven buttons is used to enter time data for the clock and timer circuits. Eight of them, plus the memory button, are used for entering preset station frequencies. Pressing one of the buttons later calls up the stored frequency and lights a correspondingly numbered red light in a row above the group of memory buttons.

The two tuning/scan buttons shift the frequency up or down in 200-kHz steps for FM and 10-kHz steps for AM. In the auto setting of the auto/manual button the tuner scans until a signal is encountered; in the manual mode it steps one channel per touch or continuously if the button is held in more than a second. A scan threshold button selects the signal level required to stop automatic scanning.

In the display window, below the frequency/time numerals, there are a number of smaller lights indicating relative signal strength, when the amplifier protection circuit has operated, whether the display is in the clock or tuner mode, and when the tuner is in its “+ 25 kHz” mode (which adds 25 kHz to the indicated frequency for use in those parts of the world having those FM-channel assignments). On the panel below the lights are the pushbuttons associated with these functions as well as the sleep switch for the timer. Also in this group are the four program-selector buttons for fm. am, phono, and aux. Pressing any of these also turns on the receiver. Across the bottom center of the panel are buttons for eq DEFEAT, SUBSONIC FILTER, 8-KHZ FILTER, loudness, and mono mode selection. To their left are switches for independent control of the two sets of speaker outputs. Immediately to the left of the digital-display window are five vertical sliders. Instead of the usual two or three tone controls, the SR 8100 DC has a five-band equalizer with center frequencies of 50, 200, 800, 3,200, and 12,800 Hz. Each slider has a maximum control range of ± 10 dB. To the left of the sliders is the power off (standby) switch and a pair of 1/4-inch phone jacks for headphones and eq out (the latter for recording an equalized program with a machine plugged into the front-panel jack).

The four knobs visible on the front panel control volume and balance, tape (for listening to the source or the playback from either of two tape decks or for dubbing from either deck to the other), and the timer switch for setting, activating, and de-activating the timer and clock functions.

On the rear of the SR 8100 DC are the various input and output jacks, two sets of insulated spring-loaded speaker-output connectors, antenna terminals, and a hinged AM loop antenna, as well as two a.c. outlets, one of which is switched. A scan selector switch changes the AM-tuning interval to 9 kHz for use in Europe or wherever that channel spacing is used.

Laboratory Measurements

Following the usual preconditioning period (during which the top of the receiver became quite hot), the 1,000-Hz output clipped at 90 watts per channel into 8 ohms, 124.3 watts into 4 ohms, and 58.3 watts into 2 ohms. The 8- and 4-ohm clipping-headroom ratings were 0.8 and 1.4 dB, respectively. Using the pulsed signal of the dynamic-power test, the clipping levels were 97.3, 163.5, and 30 watts, respectively, for the three load impedances. The 8- and 4-ohm dynamic-headroom ratings were 1.13 and 2.6 dB, respectively.

When we drove 8-ohm loads at 1,000 Hz, the distortion was about 0.001 per cent from below 1 watt to 80 watts, where it was 0.0012 per cent. Into 4 ohms, the readings were only slightly higher—in the range of 0.005 to 0.007 per cent up to 100 watts and only 0.02 per cent at 120 watts. The 2-ohm distortion was less than 0.005 per cent up to more than 30 watts output, reaching 0.1 per cent at 55 watts. Obviously the amplifier is not at its best when driving two pairs of low-impedance speakers.

Using 8-ohm loads and operating the amplifier at rated power (75 watts) and at half and one-tenth rated power, the distortion was negligible over the full audio range. The lowest reading was 0.0004 per cent at 20 Hz, and the highest was 0.024 per cent at 20,000 Hz. The high-frequency intermodulation distortion, with equal amplitudes of 19- and 20-kHz input with a peak level equal to that of a 75-watt sine wave, was at —80 dB for the third-order product (18 kHz) and —76 dB for the second-order product at 1,000 Hz.

The amplifer was stable with a reactive simulated loudspeaker load. Its slew factor was 1.7, with waveform distortion visible at 34 kHz when the amplifier was driven to rated output. Through the aux inputs, 19 millivolts (mV) drove the amplifier to a 1-watt reference output and the phono sensitivity was 0.28 mV. The respective A-weighted noise readings were —78 and — 75 dB, referred to 1 watt. The phono input overloaded at a high 235 mV at 1,000 Hz, and the equivalent readings at 20 and 20,000 Hz were 250 and 242 mV. The RIAA phono equalization was accurate within 0.5 dB overall, and it was not affected by phono-cartridge inductance.

The EQ response curves were essentially as rated in respect to the center frequencies of the controls, and each slider had a maximum adjustment range of +10, —8 dB. The loudness contours boosted both low and high frequencies as the volume setting was reduced, but the maximum boost was only about 10 dB and the sound never became objectionably heavy. The filters had not very effective gradual slopes of 6 dB per octave, with their — 3-dB points being 100 and 5,000 Hz.

The FM-tuner section of the SR 8100 DC had a usable sensitivity of 11.8 dBf (2.1 microvolts, or μV) in mono. The stereo sensitivity was determined by the switching threshold of 27 dBf (12 μV). The mono and stereo 50-dB quieting sensitivities were 15 dBf (3 μV) and 36 dBf (36 μV), respectively. The tuner distortion at 65 dBf (1,000 μV) input was 0.073 per cent in mono and 0.28 per cent in stereo. The noise level at that input was —67 dB in mono and —64 dB in stereo. The mono IHF intermodulation distortion of the FM tuner (with 14-and 15-kHz tones at an equivalent 100 per cent modulation level) was —56 dB for third-order (at 13 and 16 kHz) and —65 dB for second-order distortion at 1,000 Hz. In stereo, these were —49 and —55 dB, respectively, and there were the usual large number of spurious products between —65 and —80 dB.

The FM-tuner frequency response was down 1.4 dB at 30 Hz and up 1.1 dB at 15,000 Hz relative to the 1,000-Hz level. The channel separation was excellent, averaging 58 to 59 dB from 80 to 400 Hz and falling to 45 dB at 30 Hz and 37 dB at 15,000 Hz. Other tuner-performance measurements include a capture ratio of 1 dB (very good), AM rejection of 66 dB at 45 dBf (100 μV) input, and image rejection of 78 dB. The alternate- and adjacent-channel selectivity readings were 74 and 4.6 dB, respectively. The muting and stereo thresholds were identical, 39 dBf (50 μV) for the hi setting and 27 dBf (12 μv) for the lo setting. The 19-kHz pilot carrier leakage was —62 dB, and the tuner hum was —67 dB. The AM section was no better than adequate with a frequency response of — 6 dB at 80 and 3,200 Hz.

Comment

The Marantz SR 8100 DC is a versatile, high-quality receiver that will do all that is required of it in a competent manner, asking only that the user take the time to learn to use it properly. Although not inexpensive, it is reasonably competitive with other receivers that offer similar basic performance but without the Marantz’s extra signal-processing functions.

The audio section of the SR 8100 DC is excellent, and it is powerful enough for almost any home-listening requirements. The five-band equalizer is much more flexible than the usual tone-control arrangement, and (thanks to a comprehensive manual) all the operating controls are easy to use despite their sometimes unconventional functions and nomenclature.

The FM tuner of the SR 8100 DC is also a very good performer. Although not a “super tuner” (especially in respect to its S/N performance), it is as good as the FM-tuner section of any receiver we can recall testing recently.

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