Nikko NR-1000 Stereo Receiver Review

The Nikko NR-1000 stereo receiver features digitally synthesized FM and AM tuning with six preset “memory” channels for each of those bands. Its audio amplifier is rated to deliver 65 watts per channel to 8-ohm loads from 20 to 20,000 Hz with no more than 0.03 per cent total harmonic or intermodulation distortion.

Like most digital-synthesis receivers, the NR-1000 uses pushbuttons for its tuning functions, displaying the received frequency with 3/8-inch-high orange numerals. The band in use is identified by the orange letters am or FM, with the appropriate “kHz” or “MHz” appearing to the left and right of the numbers. The stations are tuned by a pair of flat elongated buttons below the frequency readout, which cause the receiver to scan either up or down in frequency when they are pressed.

A small tuning mode button selects either auto or manual tuning. In auto the receiver scans rapidly after a momentary touch of a tuning button, stopping only on a signal of sufficient strength. In manual the tuning advances in steps of 200 kHz (a channel width) on FM and 10 kHz on AM. In either mode, holding a tuning button in will cause the receiver to scan rapidly and continuously.

To the left of the frequency readout are several LED displays indicating relative signal strength (with five segments), stereo reception, power on, and two groups of audio-power indicators calibrated from 0.03 to 65 watts for each channel. Below the displays are the six preset tuning buttons and a memory button. To store the frequency of any station, memory and one of the preset buttons are touched in succession. A small green LED above each preset button glows when it is in use. Each button can be used to store one FM and one AM frequency. The large power button completes the horizontal row below the display area.

The receiver’s other controls are conventional in appearance and operation. They include two speaker buttons, a phone jack, bass and treble tone controls (each having eleven detented positions), a center-detented balance control, and a large volume control to the right of the display window. Small rectangular buttons provide tone-de-FEAT, SUBSONIC FILTER, STEREO/MONO mode, loudness compensation, tuning mode, FM mute, FM/AM band selection, and choice of either an MM (moving-magnet) or MC (moving-coil) phono input.

The program source is selected by pressing one of five large rectangular clear-plastic buttons aligned vertically at the right of the panel. They are marked phono, tuner, aux, tape i, and tape 2 and light up in green when engaged. A small knob next to the balance control cross-connects two tape decks for dubbing in either direction.

The rear of the NR-1000 contains the usual input and output connectors, including small insulated binding posts for the two sets of speaker outputs and the antenna input connections. The AM antenna is a small loop (not a ferrite rod) whose outputs connect to the AM-antenna terminals externally. The loop can be removed from the rear of the receiver and mounted nearby for best reception. One of the two a.c. outlets is switched. There are also two pairs of phono jacks marked adaptor (out, in), and they are joined by removable jumpers. These are almost equivalent to the pre-out/main-in jacks found on some amplifiers and receivers. However, they are ahead of the volume, loudness, mono/stereo, and infrasonic-filter circuits of the NR-1000, although they come after the tone controls and tape-recording circuits. The adaptor jacks are suitable for connecting signal-processing accessories such as equalizers, noise reducers, and expanders. The Nikko NR-1000 receiver, finished in silver grey, is 17-1/4 inches wide, 13-1/2 inches deep, and 4-1/4 inches high; it weighs about 22-1/2 pounds. Price: $620.

Laboratory Measurements

The cooling fins for the output transistors are located within the cabinet of the receiver, with heat being removed by air convection through a grille on its top cover. The grille became very hot during our preconditioning and high-power tests, but the exterior was comfortably cool during normal operation.

The output at 1,000 Hz clipped at 81 watts per channel into 8 ohms for an IHF clipping-headroom rating of 0.96 dB. Into 4- and 2-ohm loads (for which the receiver is not rated) the respective clipping power outputs were 82 and 40.5 watts. Using the tone-burst signal of the IH-F dynamic-head-room test, the output clipped at 111 watts into 8 ohms, 96 watts into 4 ohms, and 51 watts into 2 ohms. The IHF dynamic-head-room rating (8 ohms) was 2.32 dB.

At the rated 65-watts output (8 ohms) the distortion was less than 0.002 per cent below 5,000 Hz and was 0.0075 per cent at 20.000 Hz. At half power and one-tenth power the characteristics were similar, with slightly lower readings. At 1,000 Hz, the distortion into 8 ohms was undetectable, being below the “noise floor” at most power outputs. It was well under 0.001 per cent up to 70 watts, reaching 0.005 per cent at 80 watts output just before clipping occurred. The 4-ohm performance was similar, with the distortion being less than 0.0014 per cent up to 40 watts and rising to 0.04 per cent at 75 watts. The 2-ohm distortion became measurable at 20 watts, where it was 0.0027 per cent, and it rose rapidly from 0.016 per cent at 30 watts to 0.26 per cent at 40 watts.

The amplifier was stable with reactive loads, although as clipping occurred with 2-ohm loads there was a burst of high-frequency oscillation visible on the output waveform. The IHF slew factor exceeded 25. The IHF IM distortion, measured with equal-amplitude signals at 19,000 and 20.000 Hz, was unmeasurable, with no component greater than —90 dB referred to rated power output.

The amplifier sensitivity for 1 watt output was 19 millivolts (mV) through the aux input and 0.28 mV through the phono (mm) input. No measurements were made through the MC input, which has a rated sensitivity ten times higher than the MM input and a 100-ohm input impedance.

The noise levels were nearly alike for the high- and low-level inputs, measuring -79 to -81 dB (A-weighted) referred to 1 watt.

The phono-preamplifier stage overloaded at 170 mV at 1,000 Hz, and at the frequency extremes of 20 and 20,000 Hz the overload levels (converted to equivalent 1,000-Hz values) were 185 and 141 mV, respectively. The MM phono-input impedance was 46.000 ohms in parallel with a capacitance of 135 picofarads.

The amplifier tone controls had the typical Baxandall frequency response, with the low-frequency turnover shifting between 100 and 300 Hz as the bass control was varied and the treble curves being hinged at 3.000 Hz. The loudness compensation boosted both low and high frequencies at low volume settings. The infrasonic-filter response was down 3 dB at 30 Hz and 5 dB at 20 Hz. The RIAA equalization was accurate within ±0.5 dB from 20 to 20,000 Hz. The extreme high-frequency phono response was very slightly affected by cartridge inductance, rising about 0.5 dB at 20.000 Hz.

The FM-tuner section had a mono usable IHF sensitivity of 14.4 dBf (2.9 microvolts, or μ) and a stereo sensitivity of 17.2 dBF (4 μV). Its mono 50-dB quieting sensitivity was 15.3 dBf (3.2 μV) in mono and 35.5 dBF (33 μV) in stereo. At a 65-dBf (1,000 μV) input the distortion was 0.28 and 0.19 per cent, respectively, for mono and stereo modes, with corresponding noise levels of -69 and -67 dB. The two-tone IHF IM distortion measurement, using frequencies of 14,000 and 15,000 Hz, showed a 1,000-Hz difference-tone component of -56 dB in mono and -62 dB in stereo, referred to 1.000 Hz at 100 per cent modulation. The third-order components at 13,000 and 16.000 Hz were 48 and 52 dB below the modulating-tone levels for mono and stereo. In stereo, there were also a number of spurious frequencies in the output (this is typical of most FM tuners), but none exceeded a -60-dB level.

The stereo-FM frequency response was flat within ±0.6 dB from 30 to 15,000 Hz. The low-pass filters that removed multiplex pilot-carrier signals from the audio output were very effective in spite of having no effect on the frequency response at 15,000 Hz, since the 19-kHz leakage was a low — 70 dB. The tuner hum was —67 dB. The channel separation was about 38 to 42 dB at the frequency extremes of 30 and 15,000 Hz and about 45 dB throughout the midrange frequencies.

The muting threshold was factory-set at 16.2 dBf (3.5 μV) but is easily adjustable with a screwdriver by a rear-mounted control. The adjustment limits were 10.8 dBf (1.9 μV) to 62 dBf (700 μV). The stereo-switching threshold varied with the muting setting, but it was slightly lower. It was adjustable from 8.7 dBf (1.5 μV) to 61 dBf (600 μV) and the setting was 14.4 dBf (2.9 μV) as received. The capture ratio was 1.83 dB at 65 dBf input, and the AM rejection was 58 dB at the same level. Alternate-channel and adjacent-channel selectivity readings were 63 and 6 dB. The image rejection was a good 83 dB. The AM frequency response was down 6 dB at 90 and 3,700 Hz.

Comment

Many of the control features of the Nikko NR-1000 are typical of those found on modern digital-synthesis receivers in its price range. Unlike some receivers, whose tuner-memory circuits can be kept “alive” only while the receiver is plugged into a powered a.c. socket or with batteries installed in the receiver, the NR-1000's memories function for at least three days without power. We also appreciated the adaptor connectors, which make it unnecessary to usurp one of the tape-monitoring circuits for another accessory device.

Although the lights above the preset buttons show when one is engaged, they can be seen only over a restricted vertical angle, so that the receiver should be installed close to eye level if these lights are to serve any purpose. The brightly lit and highly legible selector buttons more than compensate for this minor incovenience, since they can be read from across the room. The digital frequency readout is highly visible from almost any location.

The FM tuner of the NR-1000 can be characterized as a good performer. Perhaps because of its true loop antenna, the AM tuner was less plagued by local electrical interference than most tuners, and its upper frequency-response limit of nearly 4,000 Hz almost qualifies it for “hi-fi” status, at least compared to the vast majority of AM-tuner sections on the market. At any rate, it was very listenable.

The audio amplifier, in addition to its flexibility (two tape-recorder circuits with dubbing facilities, built-in MC gain and termination, among other things), has extraordinarily low distortion at any normal listening level within the audio band. All in all, the Nikko NR-1000 impressed us as a very competently executed medium-power, full-feature receiver. If it does not boast of any “new breakthroughs,” it is also happily free of design flaws that might mar the pleasure of using it.

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