The Luxman L-400 is a Duo-Beta Circuit Stereo Integrated Amplifier, designed to deliver high-fidelity audio performance. This amplifier incorporates Luxman's proprietary Duo-Beta circuit, which is a key feature for its sound quality.
Function Description:
The L-400 serves as the central control unit for an audio system, allowing users to connect various audio sources, amplify the signals, and drive loudspeakers or headphones. It features multiple input options, including Phono (MM and MC), Tuner, AUX/DAD, and Monitor inputs (REC. 1, MONI. 1, REC. 2, MONI. 2), providing flexibility for connecting a wide range of audio components. The amplifier also includes a pre-main output, allowing it to be used as a pre-amplifier or a power amplifier in conjunction with other components.
The front panel of the L-400 is equipped with various controls for sound customization and operation. These include a power switch, input selectors, a balance control, a volume control, bass and treble tone controls, a loudness function, and a headphone jack. Speaker output terminals are provided for connecting two pairs of loudspeakers (A and B speakers), with a speaker selector switch to choose between them or use both simultaneously.
The Duo-Beta circuit is a core technology in the L-400, aimed at achieving stable and accurate amplification across the audio spectrum. This circuit design typically involves a combination of DC servo and negative feedback techniques to optimize linearity and reduce distortion.
Important Technical Specifications:
- Power Output: 55W per channel into 8 ohms, across the full frequency range of 20-20,000Hz. This indicates a robust power delivery capable of driving most home audio speakers.
- Distortion: A very low total harmonic distortion (THD) of 0.02%, signifying a clean and accurate audio reproduction.
- Input Sensitivity:
- Phono (MM): 1.8mV
- Phono (MC): 0.3mV
- Tuner: 160mV
- AUX/DAD: 160mV
- Monitor: 160mV
- Input Impedance:
- Phono (MM): 50K ohms
- Phono (MC): 100 ohms
- Tuner: 40K ohms
- AUX/DAD: 40K ohms
- Monitor: 40K ohms
- S/N Ratio (Signal-to-Noise Ratio):
- Phono (MM) (IHF-A weighted, 5mV): 90dB
- Phono (MC) (IHF-A weighted): 67dB
- Tuner (IHF-A weighted): 107dB
- AUX/DAD (IHF-A weighted): 107dB
- These figures indicate a high signal clarity with minimal background noise.
- Residual Noise: 0.5mV, further emphasizing the amplifier's low noise floor.
- Filter Functions:
- High Cut: 7KHz (-6dB/oct)
- Low Cut: 70Hz (-6dB/oct)
- Phono Subsonic: 15Hz (-6dB/oct)
- Phono (MM) Overload: 130mV, indicating its capacity to handle strong phono signals without clipping.
- Frequency Response:
- Phono (MM): 20Hz-20KHz (within +0.5dB)
- Tuner, AUX/DAD, Monitor: 10Hz-100KHz (within +0, -1.5dB)
- These wide frequency responses ensure faithful reproduction of the entire audio spectrum.
- Tone Control:
- Treble: +8dB at 10KHz
- Bass: +8dB at 100Hz
- Loudness: Volume -30dB: +8dB at 100Hz, a feature to compensate for the ear's reduced sensitivity to bass and treble at low listening levels.
- Dimensions: 453(W) x 317(D) x 111(H) mm (17.8" x 12.5" x 4.4"), making it a relatively compact integrated amplifier.
- Weight: Net 7.6Kgs, Gross 9.0Kgs.
- Power Consumption: 120V 2.3A (CSA Rated).
Usage Features:
The L-400 is designed for ease of use while offering comprehensive control over the audio experience.
- Input Selection: A rotary function selector allows for easy switching between various audio sources.
- Phono Stage: The inclusion of both MM (Moving Magnet) and MC (Moving Coil) phono inputs caters to a wide range of turntables and cartridges, a significant advantage for vinyl enthusiasts. A selector switch on the rear panel allows the user to choose between MM and MC.
- Tone Controls: Independent bass and treble controls enable users to fine-tune the sound to their preference or to compensate for room acoustics and speaker characteristics. The loudness function provides a quick way to enhance bass and treble at lower volumes.
- Balance Control: A dedicated balance control allows for adjustment of the left and right channel output, useful for correcting imbalances in speaker placement or listening position.
- Headphone Output: A front-panel headphone jack provides a convenient option for private listening.
- Speaker Selection: The ability to connect and select between two pairs of speakers (A and B) or use both simultaneously offers flexibility for multi-room setups or comparing different speakers.
- Monitor Loop: The REC. and MONI. inputs/outputs facilitate connecting tape decks or other recording devices, allowing for monitoring the recording signal.
Maintenance Features:
The service manual provides specific instructions for bias (idle) current adjustment, which is a critical maintenance procedure to ensure optimal performance and longevity of the amplifier's output stage.
- Bias Current Adjustment: This procedure involves connecting a DC Voltmeter between specific test points (TP1 and TP2 for the L-channel, TP3 and TP4 for the R-channel) and adjusting potentiometers (RV101a and RV101b) to achieve a reading of 15mV ± 5mV. This adjustment ensures that the output transistors operate in their optimal linear region, minimizing crossover distortion and maintaining sound quality.
- Parts Lists and Diagrams: The manual includes detailed block diagrams, exploded views, and schematic diagrams, along with comprehensive parts lists for various PCBs (Pre-Main AMP, Function SW, Tone Control, VR Control, HD Phone, Balance Control, MC SW). These resources are invaluable for troubleshooting, repair, and component replacement by qualified technicians.
- IC (TR) Handling Guide: Provides pinout diagrams for key integrated circuits and transistors (e.g., NJM2043D-D IC101, 2SA979G Q101a,b), which is essential information for servicing and understanding the circuit's operation.
- Component Specifications: The parts lists specify the type and value of various components (capacitors, resistors, diodes, switches, etc.), aiding in accurate replacement. For example, capacitors are identified by type (Electrolytic, Ceramic, Polyethylene, Mylar), and resistors by material (Carbon, Metal Film, Cement).
- Safety Remarks: The manual emphasizes the importance of safety, stating that critical components should only be replaced with specified Luxman parts to maintain safety standards and performance. It also advises against modifying the circuit and recommends returning the unit to a Luxman service center for repairs involving the AC cord or chassis.
Overall, the Luxman L-400 is a well-engineered integrated amplifier that combines high-quality audio performance with practical features and comprehensive serviceability, making it a valuable component for any serious audio setup.
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