Luxman L 550 (1981)
A pure Class A integrated amplifier released in 1981, notable for its single-stage voltage amplification and dual heat-pipe cooling.
Overview
The Luxman L-550 is a pure Class A integrated amplifier introduced in 1981. It was recognized as the world's first pure Class A integrated amplifier, establishing the foundation for the L-550 series that would include the L-550X, L-550Z, L-570, and L-580. This model combined high-fidelity solid-state design with tube-like sonic qualities, contributing to Luxman’s reputation for "no-compromise amplification." The amplifier delivers 50 watts per channel into 8 ohms with exceptionally low distortion and a wide frequency response.
Specifications
| Effective power | 50W + 50W (Class A Operation, 8 Ω, Double-channel Operation) |
| Amplifier class | Pure Class A |
| Total harmonic distortion factor | 0.005% or Less (8 Ω, Both Channel Operation, -3dB) |
| Input sensitivity | Phono MM:1.6mV; Phono MC:80 μV; Tuner, AUX, Monitor, Main In:220 mV |
| Input impedance | Phono MM:100k Ω, 50k Ω, 100 Ω; Phono MC:300 Ω, 100 Ω, 40 Ω; Tuner, AUX, Monitor:40k Ω; Main In:47k Ω |
| Signal-to-noise ratio (IHF-A) | Phono MM:84dB; Phono MC:80 dB (250 μV input); Tuner, AUX, Monitor, Main In:110 dB |
| Frequency characteristic | 10 Hz to 100 kHz -1dB |
| Tone control | Low turnover: 55 Hz – 620 Hz (9 steps); High turnover: 620 Hz – 10 kHz (9 steps); Maximum variation: +/- 9 dB |
| Tape monitor | Route 3 (Tape1, 2, Tape Front) |
| Tape dubbing | 4 systems (1 → 2, 2 → 1, 1 → Front, Front → 1) |
| Linear equalizer | Up tilt, down tilt: 2 steps each (1 step 1 dB) |
| Power consumption | 310W |
| External dimensions | Width 453x Height 174x Depth 460 mm |
| Weight | 21.4kg |
Design
The L-550 uses a pre-main amplifier design with the proprietary DUO β Circuit / S, combining appropriate NFB, DC-servo, and a single-stage voltage amplifier to achieve ideal signal purity. The MC head amplifier employs an FET with high transconductance and low noise, biased at 7 mA per device for optimal gain. Voltage amplification occurs in a single stage with a completely independent output stage to isolate the first stage from loading effects. The power section delivers 50W/ch through intrinsic Class A operation with fixed bias current. Heat from continuous Class A operation is managed by two large, symmetrical heat pipes that minimize thermal noise. The phono stage includes a phono straight function that bypasses tone controls and filters for direct signal path, while the Lux-style NF tone control provides smooth, precise adjustment. The power supply features a 400 VA EI core transformer treated to reduce temperature rise and two 30,000 μF capacitors made with 99.99% pure aluminum. A pre-heating function allows warm-up without powering the amplifier fully, with a warm-up indicator confirming stable operation. A line phase sensor detects AC polarity to optimize sound quality.
Context
The L-550 was the first model in a successful lineage of Luxman integrated amplifiers, launching a series known for uncompromising sound quality and innovative engineering. It helped establish Luxman’s reputation for achieving a "tube-like" sonic character from solid-state circuitry, with a smooth midrange, rich harmonics, and a deep, natural soundstage. Its release marked a milestone in amplifier design as the world's first pure Class A integrated amplifier.
Market
A known maintenance concern involves capacitor replacement in the power supply, as discussed in dedicated repair threads. One listing in the Vintage Technology Archive shows a unit priced at $1,574.
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