JVC R-X40 Stereo Receiver Review

The JVC Model R-X40 AM/FM stereo receiver is rated at 40 watts per channel output into 8-ohm loads between 20 and 20,000 Hz with no more than 0.008 per cent total harmonic distortion. Its power amplifier employs the JVC “Super-A" circuit, which dynamically varies the operating bias of the output transistors to eliminate the crossover distortion sometimes associated with class-AB or class-B amplifier operation. The Super-A circuit combines the efficiency of a class-AB circuit with the extremely low distortion of class A.

The preamplifier section of the R-X40 features the five-band graphic equalizer (in lieu of conventional tone controls) that has long been a hallmark of JVC receivers. This “S.E.A." (Sound Effects Amplifier) control system provides individual adjustments of ±12 dB in bands centered at 63, 250, 1,000, 4,000, and 16,000 Hz. The lightly detented vertical slider controls have strongly detented center positions. A front-panel pushbutton connects the S.E.A. equalizer circuits into the tape-recording outputs for recording an equalized signal.

The receiver is tuned by a quartz-controlled frequency synthesizer in 0.1-MHz steps for FM and 10-kHz steps for AM. Pushbuttons cause the tuning to scan upward or downward in frequency. There are two tuning modes: automatic and manual.

The automatic setting with the mode/scan button out provides automatic switching between stereo and mono FM reception. In this mode the tuner scans in the selected direction (with the audio output muted) until a signal of sufficient strength is encountered; then it stops and unmutes. When the tuning mode/scan button is pressed in (for manual tuning) the receiver operates only in mono. Each touch of a tuning button steps the receiver through one frequency increment; holding the button in causes it to scan rapidly until it is released. The inter-station-noise muting is disabled in this mode. The same tuning modes are available in AM reception (though without stereo, of course). An interesting feature of the JVC tuning system is the audible “beep” that accompanies each frequency step. When a station is acquired (in automatic) there is a longer beep, followed by a short one when the receiver unmutes.

The R-X40 has six tuning-memory buttons (presets), each usable for one FM and one AM channel. A frequency is put into memory by tuning the receiver to that frequency, pressing the memory button located between the tuning buttons, and then pressing one of the channel-memory buttons (each of which has a red light that shows when it has been selected). When turned on, the receiver returns to the station last tuned in.

Pushbuttons are used for input selection (am, FM, PHONO, VIDEO/AUX, and TAPE), as well as for activation of either or both of the two pairs of speaker outputs, loudness compensation, and power. Horizontal sliders are used for the volume and balance controls. A display window in the center of the panel shows the tuner frequency (with large blue-white numerals) and the presence of a stereo-pilot carrier in a received FM signal. In the left half of the display window are light groups for signal strength and output power, as well as a red tape monitor light.

On the rear apron of the JVC R-X40, in addition to the input and output phono jacks, AM and FM antenna binding posts, and a hinged AM ferrite-rod antenna, there are two sets of speaker-output binding posts, two unswitched a.c. outlets, and a slide switch that changes the AM channel spacing from the 10 kHz used in this country to the 9 kHz used in other parts of the world. A headphone output jack is behind a small plastic door on the front panel.

The JVC R-X40 is 17-1/8 inches wide, 14-1/2 inches deep, and 4-5/8 inches high. Its entire exterior is silver colored. The receiver weighs 14-1/2 pounds. The suggested retail price is $350.

Laboratory Measurements

After the amplifier was preconditioned (resulting in only a moderate temperature increase above the output-transistor heat sinks), the output waveform clipped at 55 watts per channel into 8 ohms, 74 watts into 4 ohms, and 41.4 watts into 2 ohms, with both channels driven at 1,000 Hz.

The 1,000-Hz harmonic distortion was too low to measure at most power outputs, being masked by random noise or hum levels (both of which were low). With 8-ohm loads, the distortion reached 0.0005 per cent at 40 watts, 0.0013 per cent at 50 watts, and 0.14 per cent at 55 watts. With 4-ohm loads, the distortion was 0.0013 per cent at 30 watts, rising to 0.0032 per cent at 60 watts and 0.19 per cent at 70 watts. The 2-ohm distortion measured between 0.0032 and 0.005 per cent for power outputs from 10 to 40 watts. With the pulsed input signal of the dynamic-headroom measurement, the maximum output was 66.4 watts into 8 ohms, 92.2 watts into 4 ohms, and 46.8 watts into 2 ohms. The IHF clipping headroom was 1.38 dB, and the dynamic headroom was 2.2 dB (both for 8-ohm loads).

The distortion over the audio frequency range, at all power levels, was also extremely low. It was completely unmeasurable at one-tenth rated power, and at full rated power and half power the readings were less than 0.005 per cent from 20 to 15,000 Hz. At 20,000 Hz, we had to make a THD + N measurement (total harmonic distortion plus noise), since the distortion harmonics exceeded the frequency range of our spectrum analyzer, and the inclusion of noise resulted in values from 0.01 per cent at 40 watts to 0.028 per cent at 4 watts.

The slew factor was 3.3, and the amplifier was stable with reactive loads (its IHF reactive-load rating was 1.18 dB at 63 Hz). The IHF intermodulation distortion, measured with inputs of 18 and 19 kHz, was literally undetectable, being lower than the — 100-dB noise “floor” of our measurement system. The amplifier required an input of 24 millivolts (mV) through the high-level input or 0.29 mV through the phono input for a reference output of 1 watt. The respective A-weighted noise levels (referred to 1 watt) were —78 and —74 dB. The phono input overloaded with a 110-mV input at 1,000 Hz and with inputs between 90 and 115 mV over the 20- to 20,000-Hz range. The phono input impedance was 57,000 ohms in parallel with 50 picofarads.

The audio response was perfectly flat with the S.E.A. controls centered, and when the controls were adjusted, the system had the specified effect on the frequency response. The RIAA phono equalization was flat within 1 dB overall from 20 to 20,000 Hz, and it was not significantly affected by cartridge inductance. The loudness compensation was conventional, boosting both low and high frequencies moderately as the volume setting was reduced.

The FM tuner had a usable sensitivity (mono) of 13.5 dBf (2.5 microvolts, or μW). The stereo sensitivity was determined by the switching threshold of 25 dBf (10 μV). In mono the 50-dB quieting sensitivity was 15.6 dBf (3.3 μV), and in stereo it was 38.8 dBf (49 μW). The distortion at 65 dBf (1,000 μW) was 0.087 per cent in mono and 0.46 per cent in stereo, and the corresponding noise levels were —75.5 and —69.5 dB. The mono IHF IM distortion, with modulating frequencies of 14 and 15 kHz, was — 64 dB for the 1,000-Hz difference frequency and —46 dB for the third-order components at 13 and 16 kHz (the latter figure is relative to the levels of the high-frequency tones, the former figure to 100 per cent modulation at 1,000 Hz). In stereo, the 1,000-Hz component was —56 dB, but the others were unchanged. In addition, there were the usual number of low-level intermodulation products, mostly between -60 and -70 dB.

The capture ratio was a very good 0.9 dB at 65 dBf. AM rejection was 55 dB at 45 dBf (100 μV) input. The image rejection was 51 dB, alternate-channel selectivity was 63 dB, and adjacent-channel selectivity was 9.4 dB. The 19-kHz pilot carrier in the audio was at a low — 72-dB level, and the power-line hum was —68 dB (principally at 180 Hz).

The FM-tuner frequency response was within ± 1 dB from 30 to 15,000 Hz. The stereo separation was in the range of 37 to 42 dB from 40 to 7,000 Hz, falling to about 30 dB at 15,000 Hz. The frequency response of the AM tuner section was down 6 dB at 140 and 2,400 Hz.

Comment

Although the sonic benefits of unmeasurably low distortion are debatable, it is impressive to find the amplifier of the JVC R-X40, a relatively inexpensive receiver, producing distortion levels well below the ability to our test instruments to detect, let alone measure. In fact, the entire audio amplifier section of the receiver would do credit to a much more expensive product. Unlike many competing receivers, this one is capable of functioning quite well with 2-ohm loads, so that one need have no worry about driving two pairs of 4-ohm speakers.

The tuner section is satisfactory and will certainly not limit the sound quality from the receiver (that limit, as usual, is likely to be set by the FM stations and their program sources). In several respects (notably its stereo distortion) the FM tuner does not match the superb quality of the amplifier section, but from the user’s standpoint it is always smooth, quiet, and easy to use. The signal-strength and power-output indicators on the front panel are little more than cosmetic features, however, and provide little useful information.

All in all, we found the JVC R-X40 to be enjoyable to use, attractively styled, and fine sounding. Few people require more features than it offers, and many aspects of its electrical performance are unmatched, let alone surpassed, in other receivers at far higher prices.

Read all

JVC reviews

Read all