LUXMAN M-4000A
¥ 398,000 (released in January 1980)
Commentary
This stereo power amplifier is based on the large power amplifier M-4000 released in 1975, and has been further improved by introducing the latest technology.
Equipped with LUX's own duo-beta circuit to improve sound quality.
In this circuit, an appropriate amount of NFB is applied to all bands, and a DC servo circuit is coupled to the ultra-low band to determine the characteristics of sound quality in all bands and to modify the ultra-low band out of the audible band to obtain the overall unity.
In addition, the higher the bare characteristics of the amplifier, the higher the gain (gain). In order to suppress this, a large amount of NFB is applied and the sound quality deteriorates. To solve this vicious circle, we have made an amplifier with excellent bare characteristics and low gain, and greatly reduce NFB. As a result, we eliminate TIM distortion caused by the difference between NFB application in the low and high frequencies.
In addition, the DC servo circuit reduces the ultra-low frequency noise and improves the resolution of the low-frequency reproduction by increasing the damping factor of the ultra-low frequency. It also solves the DC drift problem and protects the speakers.
Four power MOS FETs are used for the output stage, a bias current of 300 mA or more is supplied, and a high-speed driver circuit is combined to achieve a notchless class A operation without switching operation.
In order to realize an amplifier with low gain and good bare characteristics suitable for duo-beta circuits, we have conducted a thorough review of the circuit configuration and materials to pursue bare characteristics.
The first stage consists of a cascode differential amplifier composed of a dual monolithic type FET resistant to changes in ambient temperature and voltage and a high-voltage low-noise transistor to obtain excellent high-frequency characteristics. The pre-drive stage adds a current mirror load to the cascode differential amplifier circuit to improve linearity. The drive stage and the output stage consist of a pure complimentary service SEPP circuit to extract large outputs at a low distortion rate.
As a result, the naked distortion factor is 1/5 of the conventional amplifier, and the naked frequency characteristic is extended by one order of magnitude.
In order to completely eliminate interference between the left and right channels of the input signal, the entire circuit including the left and right completely independent power transformer is made into twin monaural, and two monaural amplifiers are integrated.
To simplify wiring, the circuit board is made into blocks and glass epoxy, which is highly reliable and does not change over time, is used. In addition, highly reliable connectors often used in communications equipment are connected to the circuit board, and gold plating is applied to the terminals on the circuit board side to increase the reliability of the carefully selected employment.
The power supply section employs two large toroidal transformers with good regulation and is combined with a twin monaural high-speed constant voltage power supply.
The output stage uses a 15,000 μ Fx2 high-capacity capacitor for sound quality, and the pre-driver stage is fixed to a constant voltage to create a strong power supply.
The M-4000A is equipped with a three layer protection circuit.
One is the speaker protection circuit, which works when an excessive DC input is input and a DC component is detected at the output terminal.
In addition, when a large input is applied while the + - terminal of the speaker terminal is short-circuited, a protection circuit for detecting overcurrent and a protection circuit for detecting power transistor fuse blow protect the double amplifier.
It is a metal coated type and uses the same type of detent volume as a high-grade attenuator.
It uses a chimney type heat sink made of aluminum die-cast.
It is equipped with a subsonic filter to cut out ultra-low frequency noise, which causes intermodulation distortion, as well as to prevent DC input.
The input terminal is gold-plated to improve reliability, while the output terminal uses a cannon connector.
Ground terminal is mounted.
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Model Rating
| Type | Duo Beta Circuit Stereo Power Amplifier |
| Continuous effective output (20 Hz to 20 kHz ; Simultaneous operation for both channels / single channel operation) |
270W + 270W (4 Ω) 180W + 180W (8 Ω) |
| Total Harmonic Distortion Factor (8 Ω, 20 Hz to 20 kHz) | 0.008% or Less (180W) |
| Intermodulation distortion factor (8 Ω, 60 hz : 7 khz = 4 : 1) | 0.008% or Less (180W) |
| Frequency characteristic | 3 Hz to 100 kHz - within 1 dB |
| Output bandwidth | 10 Hz to 100 kHz -3dB (0.1%) |
| Input Sensitivity / Impedance | 600mV/50k Ω |
| Signal-to-noise ratio (IHF-A corrected) | 116 dB or more |
| Residual noise | 0.2 mV or less |
| Crosstalk (Volume Max) | -100dB or less (1 kHz) -80dB or less (20 Hz to 20 kHz) |
| Damping factor | 100 (at 8 Ω Load) |
| Protection circuit | Speaker protection circuit by DC drift of speaker terminal Amplifier protection circuit by overcurrent detection Amplifier protection circuit by detecting fuse blown for power transistor |
| Attachment | Power meter Peak Indicator (With Peak Indicator On / Off Switch) Meter Sensitivity Selector Switch (0 db, -20dB) Input level set with 1-dB interval 22-point / detent volume |
| Power supply voltage | 100 VAC, 50Hz/60Hz |
| Power consumption (Electrical Appliance and Material Control Law) | 520W |
| External dimensions | Width 491x Height 181x Depth 390 mm |
| Weight | 30kg |
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