LUXMAN L-550

Commentary

Pre-main amplifier with DUO β circuit / S.

We have developed the DUO β Circuit / S, which combines an "appropriate amount NFB" and a "DC-servo", and the DUO β Circuit / S, which adds a "single-stage amplifier" in addition to the control feedback power supply plusX, which is superior in sound quality. These circuits are installed in the equalizer and power section.
The first stage amplifier uses an FET for the MC head amplifier in the first stage. Originally, this FET has high gm and low noise, and it has a structure in which a large current of 7 mA per 1 stone is applied to obtain the necessary gain.
At the same time, the output stage is completely independent so as not to affect the first stage, and the second stage is removed. This realizes an ideal circuit with only one stage for voltage amplification.

The output section has an intrinsic class A operation with fixed bias current, and realizes a large output of 50W/ch.
The large amount of heat generated by class-A operation is handled by two large heat pipes, which are symmetrical in shape to eliminate heat radiation noise.

A single-stage amplifier is also used for the head amplifier.
The PNP transistor with very low input equivalent resistance at the first stage is made to be single differential, and low noise is realized while obtaining sufficient gain.

It is equipped with a phono straight function that separates the input selector, filters, monaural switch, balance control, etc., and connects the equalizer and power amplifier directly.

In some cases, the recording frequency of a disc, etc., rises gradually toward the high frequency range, and in other cases, it falls. Therefore, a linear equalizer is incorporated to correct this tendency and return the recording characteristics to a flat level.

It is equipped with a tone control that allows you to select nine turnover frequencies for both high and low frequencies.
It is designed with emphasis on the frequency at which the change starts rather than the amount of change, and uses the NF type Lux-style tone control that can obtain straightforward change characteristics.

The power supply section uses a special EI core with a capacitance of 400 VA, and a power transformer with the inside hardened by 哇砂 to suppress temperature rise.
Two electrolytic capacitors with an aluminum purity of 99.99% and a capacity of 30,000 μ F with sound quality measures are used.

Equipped with a pre-heating function, it can be heated by passing a small amount of current.

Equipped with a warm-up indicator, it is possible to confirm that stable operation has started.

Equipped with a line phase sensor, it can control sound quality by detecting the polarity of the AC power supply in the process.

Model Rating

Type	Integrated amplifier
Effective power	50W + 50W (Class A Operation, 8 Ω, Double-channel Operation)
Total harmonic distortion factor	0.005% or Less (8 Ω, Both Channel Operation, -3dB)
Input sensitivity	Phono MM:1.6mV Phono MC : 80 μ V 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 μ V input) Tuner, AUX, Monitor, Main In : 110 dB
Frequency characteristic	10 Hz to 100 kHz -1dB
Tone control	Low turnover : 55 Hz, 77 Hz, 110 Hz, 155 Hz, 220 Hz, 310 Hz, 440 Hz, 620 Hz, 820 Hz High turnover : 620 Hz, 880 Hz, 1.2 kHz, 1.7 kHz, 2.5 kHz, 3.5 kHz, 5 kHz, 7 kHz, 10 kHz 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