Mitsubishi M-AV1
A charcoal-gray A/V receiver that promised to be the master control for an entire home theater - and then stumbled badly on the test bench.
Overview
The M-AV1 doesn't look like other receivers. Mitsubishi's own four-color brochure declared that "a concept as big as Home Theater called for a new look at the heart of the system," and the company meant it literally. The finish is charcoal gray rather than the black that dominated the category. A hinged flap hides most of the front-panel controls, so only the power switch and a large calibrated volume control sit out in the open. A multi-colored display reports just about everything happening in the system, and the display angle can even be adjusted for best viewing. Audio (February 1990, p.77) called it a receiver that "looks like no other stereo receiver" the reviewer had ever seen, and praised the ergonomics and clean appearance before the measurements began.
The front panel is clever. Behind the flap sit a stereo phone jack, an A or A+B speaker selector, audio and video record selectors, and a pair of buttons that cycle through the audio functions - FM mode, surround, surround volume, bass, treble, tone defeat, loudness compensation, subsonic filter, high-cut filter, and record monitor. The display shows the selected input, tuned frequency, audio function status, stereo reception, center tuning, muting, amplifier clipping, and Dolby Surround activation. A supplied remote duplicates the major front-panel functions and has its own illuminated display with a backlighting switch for night use. A sliding cover on the remote opens to reveal controls for other Mitsubishi audio and video components.
The connectivity is what makes the M-AV1 a system hub. The rear panel carries seven pairs of audio input jacks, four coaxial video inputs plus two S-video (Y/C) connectors, two coaxial video outputs with an S-connector output, three pairs of audio output jacks, a 75-ohm F-type antenna connector, 300-ohm antenna terminals, and terminals for the supplied AM loop or an external AM antenna. Five convenience AC outlets are provided, three switched and two unswitched. The color-coded speaker binding posts are spaced to accept standard double-banana plugs. Two sets of speakers can run in stereo. With the switch set to Surround and matrix or Dolby Surround selected, four properly positioned speakers can deliver surround sound. An "Audio Control Bus" multiconductor connector lets ribbon cables link the receiver to other Mitsubishi components so the single remote can run the whole stack. A signal processor can be inserted by pulling two wire jumpers that normally bridge the preamp and power amp sections.
The amplifier section is rated at 125 watts per channel into 8 ohms for the front channels, with 25 watts per channel feeding the rear surround channels. A 20-millisecond time delay is encoded into the rear channels to increase depth perception and maintain separation from the front speakers. Mitsubishi's Dynamic Delay Line is claimed to expand rear-channel dynamic range by as much as 40 dB over conventional designs. The preamp uses a low-noise dual J-FET, the tone circuitry uses an IC developed specifically for audio equalization, and the output stages are discrete rather than integrated. The power amplifier employs a dual feedback loop - a main loop offering DC amplification and a secondary servo that filters DC and near-DC signals via a capacitor in the feedback path. Thermal sensors monitor output transistor temperature and adjust bias, and the speaker terminals are relay-protected and internally fused. Video switching uses a C-MOS IC network to preserve full signal amplitude, and therefore full brightness, through the receiver.
The test bench told a different story. Audio (February 1990, p.78) measured the front channels delivering the rated 125 watts into 8 ohms without trouble. Total harmonic distortion plus noise, though, was far above the 0.05% Mitsubishi claimed - 0.2% at 1 kHz, 0.14% at 20 kHz, and 0.08% at 20 Hz at rated output, with switching distortion visible on the oscilloscope at all levels. SMPTE-IM distortion ran about 1.3% at rated output into 8 ohms and stayed above 1% even at lower levels. CCIF IM measured 0.2% at the equivalent of rated power. Damping factor was approximately 30, and dynamic headroom was a substantial 2.8 dB. Mitsubishi published no 4-ohm rating, but clipping occurred at roughly 180 watts per channel at 1 kHz and around 160 watts at 20 Hz and 20 kHz. Signal-to-noise for the front channels was 75.2 dB, with input sensitivity of 15 mV for 1 watt out.
The tuner drew equally mixed notices. FM frequency response was flat within ±1 dB from 30 Hz to 15 kHz with tone controls defeated, but sensitivity was poor. With a good outdoor antenna the reviewer logged about 40 usable signals against the 50-plus a hot tuner would pull, and the blend control was needed to quiet several of the 33 stereo stations received. The AM section's response ran from roughly 80 Hz to 2 kHz between the −6 dB points. The worst problem was the spectrum analyzer's look at the 19-kHz pilot. It was unfiltered, only 34 dB below 100% modulation. That residual signal would wreak havoc on any tape deck using Dolby noise reduction when recording off the air, which is a serious flaw in a machine built to be a centralized A/V control center with connections for two tape decks.
The phono stage was workmanlike: 0.25 mV sensitivity for 1 watt out, RIAA deviation under 0.65 dB at any frequency, and a 68 dB A-weighted signal-to-noise ratio. Input overload arrived at just 85 mV, where 100 mV is considered adequate for moving-magnet cartridges. The subsonic filter's 3-dB point landed at 18 Hz as specified, and the high-cut filter's landed between 6 and 7 kHz. The loudness control's boost progressed gradually across volume settings down to −40 dB. Rear-channel response was identical in matrix and Dolby Surround modes, with a 3-dB cutoff near 8 kHz.
In listening, the reviewer found that distortion above 0.2% at high levels didn't spoil the enjoyment of CDs. Low-level crossover distortion was audible in quiet passages, though, and occasional IM distortion seemed present on complex orchestral works. The on-screen display mirrored receiver information on a connected TV monitor, even showing "Audio Volume Up" as the motorized master volume moved, and the reviewer called it a genuine delight. Audio (February 1990, p.78) concluded that less sensitive ears might not be bothered by the failure to meet specifications, and that the splendid layout and convenience features could outweigh the bench results for some buyers. For others, no amount of flexibility could excuse distortion figures that didn't start with a couple of zeros after the decimal point.
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