Luxman LV-105 Integrated Amplifier Review

Luxman calls its new LV-105 a “Brid” (hybrid) integrated audio/video amplifier because it uses vacuum tubes in combination with transistors, FET’s and MOSFET’s. Other amplifiers have been designed with various hybrid circuit configurations, but the Luxman Brid is a combination we had not previously encountered—its vacuum tubes follow the field-effect-transistor (FET) low-level stage and drive the power-MOSFET output stages. According to Luxman, the 6CG7 twin-triode tubes used in the LV-105 are more linear than conventional transistor driver stages, and they have greater bandwidth and lower phase shift.

The LV-105 has two power supplies, the larger of which operates its audio transistor stages while the other supplies the voltages for the vacuum-tube stages. When the amplifier is turned off, the tubes go into a standby “pre-heating” mode in which their heaters operate on a reduced voltage (about 80 percent of normal) and their plate voltage is reduced by half.

The Luxman LV-105 is rated to deliver up to 80 watts per channel into 8-ohm loads, from 20 to 20,000 Hz, with no more than 0.3 percent total harmonic distortion. The dynamic power output is given as 200 watts per channel into 4-ohm loads, and it is also rated for 200 watts with 2-ohm loads.

In addition to its complete audio control facilities, the LV-105 is designed to serve as a video control center. As many as three audio/video (A/V) sources—VCR’s or videodisc players (VDP’s)—can be connected at the same time, two in the rear and one in the front, though only two of them can be switched simultaneously.

The audio control facilities of the LV-105 are extensive. There are inputs for a moving-magnet (mm) or moving-coil (mc) phono cartridge, a tuner, a CD player, and two tape decks as well as the two audio/video sources. All switching is done by pushbuttons, with the selected source identified by a light. There are independent recording source selectors, including switches for dubbing from either audio deck to the other and for video dubbing (from AV SOURCE 2 to AV 1 only).

Other front-panel buttons individually activate the two sets of speaker outputs and select the mm or mc phono inputs and the front or rear AV 2 inputs. Small knobs operate the bass and treble tone controls and adjust channel balance.

The rear apron of the LV-105 contains insulated binding posts for two sets of speaker outputs and six AC convenience outlets, three of them switched. The all-black LV-105 measures 17-1/4 inches wide, 13-5/8 inches deep, and 5-3/4 inches high. It weighs 23 pounds, 6 ounces. Price: $700.

Laboratory Tests

During our one-hour, one-third-power preconditioning of the LV-105, its thermal-protection circuits repeatedly shut the amplifier down. Moreover, it did not return to operation automatically after a cooling period. Following a shut-down, we had to turn it off and turn it back on again several minutes later. Fortunately, however, the amplifier never became warm enough to interrupt our measurements even during our high-power testing. And during normal listening periods, it remained cool and never shut down.

With both channels driven at 1,000 Hz, the outputs clipped at 97 watts into 8 ohms and 106 watts into 4 ohms. Although some of the brochures on the LV-105 indicated a dynamic power capability of 200 watts into 2 ohms, its output-cur-rent protection circuits shut it down at only 28 watts continuous output into that impedance. Our measurements confirmed that the LV-105 has a good dynamic headroom of 2.58 dB into 8 ohms, equivalent to 145 watts. Into 4 ohms, the dynamic power was 190 watts, essentially confirming the rated performance, but with 2-ohm loads the protective relay silenced the outputs momentarily even with 20-millisecond bursts at under 150 watts.

The tone-control characteristics of the LV-105 were unusual, although they appeard to conform reasonably well to the rated maximum-variation range of +8, —5 dB. The controls had a considerable effect on the midrange level, and the treble control varied the volume about as much as it did the frequency response. The RIAA phono equalization was extraordinarily accurate,, varying only +0.3, —0.1 dB from 20 to 20,000 Hz.

The distortion characteristic of the LV-105 was unlike that of most amplifiers we have tested. Driving 8-ohm loads, the amplifier’s distortion at rated power and half power was about 0.002 percent from 20 to 100 Hz, rising linearly at higher frequencies to a maximum of just over 0.3 percent at 20,000 Hz. At one-tenth rated power, the low-level distortion was about 0.006 percent, and the curve matched that of the higher-power characteristics above 1,000 Hz. When we drove 8-ohm loads at 1,000 Hz, the distortion was a constant 0.05 percent from 0.1 to 2 watts, decreasing to about 0.01 percent between 20 to 90 watts. With a 4-ohm load, the distortion decreased smoothly from about 0.07 percent at 0.1 watt to the range of 0.015 to 0.02 percent between 5 and 95 watts output.

We also measured the “power envelope” of the LV-105, using burst durations (into 8 ohms) between 20 and 300 milliseconds and a total measurement interval of 500 milliseconds. From a maximum output of 145 watts during a 20-millisecond burst, the output at clipping decreased to 120 watts for 100-millisecond bursts, 115 watts for 200 milliseconds, and 105 watts for 300 milliseconds. The amplifier’s- slew factor was 25 (at 500 kHz, a rated-power sine wave took on a triangular shape). It was stable with simulated reactive speaker loads and had a reactive-load factor of 1.19 dB at 63 Hz.

Comments

The Luxman LV-105 is an interesting amplifier, partly because of its novel hybrid design and partly because of its highly versatile and functional audio/video control features. It is also attractively styled and has a functional panel layout. We chose to disregard the strange behavior of its tone controls, but anyone who often uses tone controls may wish to take this into account. In fact, the LV-105’s limited current-output capability, evidenced by an inability to drive 2-ohm loads effectively, was the only significant performance shortcoming we discovered. On the other hand, it has a considerable short-term output power capability, demonstrated by its dynamic headroom and dynamic-power measurements, and an unusually low noise level.

We must admit to doubts about the practical significance of Luxman’s “Brid” circuit design. Although the distortion characteristics of the LV-105 are unlike those of most amplifiers we have tested, they should not have any effect on its sound, and as far as we could determine, they did not. In the amounts present in any modern amplifier, ordinary nonlinear distortion is simply not a factor in sonic performance. Our “bottom line” judgment on the novel circuit configuration of the Luxman LV-105 is essentially that it is an unproven benefit, but it has no apparent negative effects on the amp’s performance.

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