Luxman L-58A (1979–1981)
The L-58A is one of the most respected integrated amplifiers Luxman produced in the late 1970s - part of what The Vintage Knob called "the classiest Luxmans ever made." It came out in Japan in 1979 at ¥149,000, which put it at the low end of high-end audio by Japanese standards. Luxman still made it the centerpiece of its stand at the 1979 Japan Audio Fair.
The big idea is Luxman's "Duo-Beta" circuit. It uses a dual negative feedback loop plus a DC servo, and the aim was to improve the amplifier's inherent (open-loop) characteristics rather than mask them with large amounts of NFB. The output stage uses MOS FETs (2SK134/2SJ49) biased at 300mA or more. Luxman called this "Notchless Class A." The high bias keeps the output devices in Class A for most practical listening levels, which avoids the switching distortion of conventional Class AB designs. The power amp section's bare distortion was improved to 0.4% (from 2-5% in conventional designs) and slew rate to 300 V/µs. The phono equalizer uses a cascode bootstrap circuit with four FETs at the input. The MC head amp has an automatic gain adjustment that adapts to the impedance of the connected cartridge.
Rated output is 100W + 100W into 8Ω (20 Hz–20 kHz) at 0.015% THD. The preamp section offers a wealth of flexibility: phono MM and two MC inputs (MC-1 at 1.5mV/100Ω direct to equalizer; MC-2 at 0.05mV–0.15mV with the auto-gain head amp), two aux inputs, two tape loops with two-way dubbing, and pre/main separation for external processing. Tone controls use the LUX NF type with switchable turnover points (bass at 150/300/600 Hz, treble at 1.5/3/6 kHz), plus a tone bypass, subsonic filter (15 or 30 Hz), high filter (9 or 15 kHz), and a two-position low boost. The cabinet is real wood — rosewood in some examples — with the chassis hollowed out around the circuit boards and ultra-thin aluminum foil shielding to minimize eddy current distortion. Dimensions are 466 × 181 × 378 mm, weight 15.3 kg.
The L-55A looks identical but is less lavishly built, and it shared its service manual with the L-58A. The later L-68A (1980) was an upgraded version with the Plus-X circuit and Line Phase Sensor. A US-market variant sold as the L-580 added LED meters in the style of the M-120A power amp. That was a Lux Corporation of America request, so it appears in no Japanese documentation. The Vintage Knob calls the L-58A "part of Luxman's all-time transistor best," and it has sold on eBay for as much as $2,650, though current market pricing is undocumented.
- Output: 100W + 100W (8Ω, 20 Hz–20 kHz, 0.015% THD)
- Output stage: MOS FET (2SK134/2SJ49), Notchless Class A, 300mA bias
- Circuit: Duo-Beta (Dual NFB + DC Servo)
- Inputs: Phono MM, MC-1, MC-2 (auto-gain), Tuner, Aux 1/2, Tape 1/2, Main-in
- Dimensions: 466 × 181 × 378 mm; 15.3 kg
- Price (Japan): ¥149,000
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