Harman Kardon hk880 Vxi A/V receiver Review

The Harman Kardon hk880 Vxi high-voltage/high-current receiver has a dualvoltage power supply controlled by a rear-apron switch. The high-voltage setting enables it to drive 8-ohm speakers at full power with low distortion. The reduced-voltage setting, for use with lower-impedance loads such as 4-ohm or even 2-ohm speakers, lowers the operating voltage of the output transistors, minimizing heat dissipation with only a minor effect on maximum power output. The hk880 Vxi is rated to deliver 60 watts per channel from 20 to 20,000 Hz into either 8 or 4 ohms with respective distortion levels of 0.08 and 0.3 percent.

Although the hk880 Vxi has a full complement of controls and exceptional flexibility, it presents a clean, uncluttered appearance. Its display window, only 5-1/2 inches wide and 5/8 inch high, is compact and subdued, yet complete. The tuner frequency is most prominent, displayed in pale-green fluorescent numerals almost 1/2 inch high, and the preset channel number (if applicable) is shown about half its size. Other data appear as required in slightly smaller letters, including indicators for the seek tuning mode, the presence of a receivable signal, the selected frequency band (FM1, FM2, AM), stereo reception, and relative signal strength. The two rectangular tuning controls are located to the right of the display window and are impossible to confuse with any other controls.

Each of the six preset buttons can be assigned to two fm frequencies and one am frequency. The total preset capacity of eighteen channels, though not uncommon among high-end automobile receivers, is one of the greatest we have seen in a home component, and programming the presets is remarkably easy to accomplish.

Six bar knobs in a row across the lower part of the panel control bass, treble, balance, and program-source selection. The VCR/Tape monitor switch feeds the amplifier input from the output of either of two tape decks, which are designated VCR 1 and VCR 2/DAT, although they can be any type of deck (or, indeed, any other line-level audio source). The source setting of this switch transfers control to the function (input) selector, which has positions for phono, CD, tuner, and A/V inputs. The a/v position can be used for playing mono or stereo audio signals from a TV set, MTS adaptor, or videodisc player. The RECORD OUT knob has a source position, which connects the selected listening source to the tape-recording outputs, and positions for dubbing in either direction.

Both the VCR/TAPE MONITOR and FUNCTION switches have an extra position marked REMOTE, which transfers control of the switch setting to the wireless remote-control unit supplied with the receiver. Red lights above the corresponding receiver knobs show their current settings during remote operation. The remote control also operates preset selection, band changing, tuning in either seek or manual mode, and volume adjustment. Its up and down volume buttons activate a motor that turns the receiver’s large volume-control knob. The remote control also has a power button that switches the receiver between its operating and standby conditions.

The remaining front-panel controls are small pushbuttons that can switch the loudness-compensation circuit, the subsonic filter, mono/stereo mode and auto-seek/manual tuning, the speaker outputs, and the external-processor jacks through which an accessory such as an equalizer or surround processor can be connected into the system.

The rear apron contains the signal input and output jacks, insulated binding posts for the two sets of speaker outputs (which accept stripped wire ends but not banana plugs), and terminals for a supplied wire-loop am antenna and a 300-ohm or coaxial 75-ohm fm antenna. The detachable AM antenna can be installed on the rear of the receiver but requires 7 inches of rear clearance. One of the two AC outlets is switched. The switch that controls the power-supply voltage is labeled SPEAKER OPERATING MODE (4 or 8 ohms). The hk880 Vxi measures 17-3/8 inches wide, 14-1/2 inches deep, and 5-1/4 inches high, and it weighs 22 pounds. Price: $749.

Lab Tests

Our audio measurements of the hk880 Vxi were made with the 4-ohm (high-current) setting of the speaker-mode switch, augmented by additional tests of clipping and dynamic power output using the 8-ohm (high-voltage/high-current) setting with 4- and 8-ohm loads. Neither the hour of preconditioning nor the subsequent high-power testing made the receiver’s top surface uncomfortably hot.

The 1,000-Hz clipping-level output into loads of 8, 4, and 2 ohms was 57.8, 81, and 109 watts, respectively. The corresponding dynamic power outputs were 76.5, 140, and 200 watts. With the switch set for 8-ohm speakers, the clipping-level power was 81.3 and 113 watts into loads of 8 and 4 ohms, and the dynamic output was 126 and 200 watts. The slew factor exceeded 25.

The amplifier section clipped softly because of its relatively low overall feedback of 20 dB. The waveform rounded smoothly when the amplifier was overdriven, but the resulting distortion rarely extended beyond the third harmonic (high-feedback amplifiers often generate odd harmonics up to the eleventh harmonic or higher under these conditions).

The input sensitivity for a reference 1-watt output was 18.8 millivolts (mv) through a high-level input and 0.275 mv through the phono input. The respective A-weighted noise levels were — 80 and -79 dB.

The bass control’s turnover frequency shifted from a maximum of 300 Hz to below 100 Hz as the knob was turned from center. The treble control’s response curves were hinged at about 2,000 Hz. The subsonic filter reduced the response by 0.5 dB at 30 Hz and to — 3 dB at 10 Hz. The RIAA phono-equalization error was less than 0.1 dB from 20 to 2.000 Hz, reaching -1.7 dB at 20.000 Hz. The loudness compensation boosted both the low and high frequencies moderately, with respective maximum boosts of 9.5 and 5 dB at any volume setting below -30 dB.

The FM tuner of the hk880 Vxi operated with low distortion at any usable signal level in both mono and stereo. The measurements of total harmonic distortion (THD) plus noise consisted principally of the distortion component, which was typically 0.1 percent or less; the noise was substantially lower. Since noise, in the form of hiss, is generally the first symptom of insufficient signal strength in fm reception, the tuner gave a strong subjective impression of high sensitivity.

To our surprise, the demodulated stereo output of the tuner contained high levels of ultrasonic signals from the pilot carrier and the demodulation process. The 19-kHz component was at a — 36-dB level, and 38-kHz signals were at —38 dB, yielding an apparent stereo distortion level of about 3 percent! Most tuners designed for home use have filters that remove most of these ultrasonic signals, which can interfere with the operation of Dolby noise-reduction circuits in tape decks. Harmonics of these ultrasonic signal components can also “beat” (interact) with the bias-oscillator frequency of a tape deck, introducing “birdies” and other noises. We had to use an external, steep-cutoff, 15,000-Hz low-pass filter in order to measure the tuner’s actual stereo distortion, which was a low 0.1 percent.

The receiver’s other fm tuner measurements were good, if not necessarily outstanding. The stereo threshold/muting level of 28 dBf (13.8 μv) was close to the 50-dB quieting sensitivity of 35.5 dBf (32.8 μv), which had the practical effect of providing quiet, low-distortion reception from almost any receivable signal. The fm frequency response was flat within +0.4, —0.1 dB from 30 to 15,000 Hz. Stereo channel separation was flat across most of the audible frequency range, reading between 37.5 and 40.5 dB from 45 to 15.000 Hz. The am tuner’s frequency response rolled off rapidly above 1.000 Hz, reaching -6 dB at only 2,100 Hz.

Comments

When we first listened to stereo fm broadcasts through the hk800 Vxi, using a simple indoor folded-dipole antenna (our normal practice before making any measurements), the clean and noise-free sound seemed too good to be true. Further investigation showed that the receiver was operating in mono. After we pressed the seek button to change mode, the display indications (and program) left no doubt that the receiver was operating in stereo, but the noise level did not change significantly!

It did not take long to confirm our initial impression that all signals— stereo as well as mono—seemed to have markedly lower noise levels than we are accustomed to hearing from receivers (or, for that matter, from many advanced separate fm tuners) using the same indoor antenna system. In addition to low hiss, the garbling distortions of multipath reception were conspicuous by their absence (our indoor antennas are an excellent source of multi-path). The key question then was whether these effects were real or merely the result of a purely personal reaction to an unconventional product design.

Measurements tended to confirm the reality of the quiet, clean fm sound of the hk880 Vxi. The tuner’s steep quieting curve and low distortion, though not unique, were considerably better than average. Its operation was free of unwelcome artifacts; there were no noise bursts or other unexpected effects when we operated any of the controls.

What about the rest of the receiver? Playing CD’s through several different speaker systems yielded uniformly satisfactory results. Since we do not, in general, find significant audible differences between good amplifiers, it was not possible to establish the degree to which the hk880 Vxi’s amplifier section was contributing to its excellent sound. But it was apparent that the hk880 Vxi did not sound like a “60-watt” receiver; it could be played at high levels into inefficient speakers without sounding strained. Its high current-output capability, demonstrated in our 2-ohm measurements, and excellent dynamic headroom are possible explanations for this quality.

Although we would hesitate to use the hk880 Vxi for recording fm broadcasts on a tape deck lacking a good low-pass input filter, because of the ultrasonic components in its tuner output, our only real criticism involves its instruction manual. Besides such lapses as giving an incorrect location for the loudness-control button, the manual is occasionally vague about some of the control functions, which are not necessarily evident from the front-panel markings. A good example is the failure to state clearly that pressing the seek button also switches the tuner between its mono and automatic stereo modes.

Overall, we give high marks to the Harman Kardon hk880 Vxi, a very much above-average receiver housed in an unassuming but practical exterior. Although it sometimes appears that all receivers are pretty much alike, the hk880 Vxi shows that some still stand out from the crowd.

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