Luxman L-68A (1980)
The Luxman L-68A is a heavy integrated amplifier from December 1980, priced at ¥188,000 in its home market. It sits at the top of Luxman's two-digit L series, the "signature" line, and is often described as the biggest and last of that family. It weighs 15.5kg and is 478mm wide. It pairs well with demanding, difficult-to-drive speakers, and owners frequently cite JBL models as a natural match.
The design centers on Luxman's "Duo Beta plus-X" topology. The Duo-Beta circuit was Luxman's answer to the TIM distortion debate of the late 1970s. It applies a moderate amount of negative feedback to an amplifier that already performs well on its own, which avoids the sonic penalties of excessive NFB. The "plus-X" power supply is a hybrid. It keeps the advantages of an unregulated supply and addresses its weaknesses with controlled, frequency-selective feedback. The output stage uses power MOS FETs, which inherently avoid the switching distortion of bipolar transistors, and the L-68A runs them with a generous idle current for optimal linearity. A large power transformer and a pair of 15,000 µF audio-grade filter capacitors back up the power stage.
The phono section is elaborate. The equalizer uses the Duo-Beta circuit too, with a cascode-connected bootstrap differential current mirror input stage built around selected low-noise FETs. The MC head amplifier is DC-coupled, with parallel N-channel FETs. A front-panel impedance switch lets you match the load to your cartridge while automatically adjusting gain. A phono straight switch removes non-essential circuitry from the disc playback path entirely. The tone control section is a Luxman NF-type design with switchable turnover frequencies (150/300/600 Hz for bass, 1.5/3/6 kHz for treble), and it can be bypassed completely when not needed. A line phase sensor on the front panel lets you check the polarity of your AC supply.
The L-68A delivers 110W + 110W into 8 ohms from 20 Hz to 20 kHz, with total harmonic distortion rated at 0.008% or less. Frequency response for line-level inputs runs from 10 Hz to 100 kHz (-1 dB), and the phono stage (MM and MC-1) holds ±0.2 dB from 20 Hz to 20 kHz. Signal-to-noise is rated at 100 dB or more for high-level sources and 80 dB or more for phono. Audio Database records the full specification set, including an unusual detail: the chassis is hollowed out beneath the circuit boards, and the whole thing sits in a rosewood cabinet with minimal aluminum shielding. This was Luxman's way of minimizing the metal chassis's influence on the circuitry.
Owner commentary, largely from Russian and Vietnamese forums, is consistently positive. One forum user preferred the L-68A to the Luxman L-510, though they found the phono stage a bit simpler than the 510's. Another described the sound as having high musical resolution with a slight "Luxman cheerfulness," a small coloration that doesn't detract. The usual caveats apply for a forty-year-old amplifier. One repair video documents pop noises being fixed, and used units on the Japanese market are typically described with modest condition grades rather than as pristine collectibles.
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