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Luxman was founded in 1925 by Tatsuya Yoshikawa and his younger brother, Yoshikazu Yoshikawa, in Japan. Originally, the company started as Kinsuido, focusing on importing and selling radios and parts, which were quite rare in Japan at the time. Luxman later shifted toward manufacturing its own high-fidelity audio equipment, establishing a reputation for quality, craftsmanship.
The Luxman L-4, produced in the early 1980s, is a well-regarded integrated amplifier known for its warm sound and reliable design. The L-4 uses a class AB design with a straightforward power stage aimed at delivering clean sound with minimal distortion.
Here are some key points of its power stage design:
1. Push-Pull Output Stage: The Luxman L-4 employs a push-pull configuration in its output stage, which is common in class AB amplifiers. This configuration minimizes crossover distortion by using both NPN and PNP transistors that share the load, effectively canceling out certain distortions and enhancing overall linearity.
2. Complementary Transistor Pairing: The amplifier typically uses a complementary pair of output transistors. This approach provides a symmetrical response, allowing both halves of the audio waveform to be accurately reproduced. Luxman was known for careful transistor matching, contributing to the smooth, natural sound for which it was famous.
3. Direct Coupling: Luxman amplifiers often employed direct-coupled designs to eliminate capacitors in the signal path, aiming to preserve audio clarity. Direct coupling offers better low-frequency response but requires a stable DC offset to avoid sending unwanted DC signals to the speakers.
4. Power Supply: The L-4 has a robust power supply design with a large transformer and sufficient filtering to provide clean, stable power to the output stage. This helps the amplifier maintain high current delivery and prevents distortion during dynamic passages.
5. Protection Circuitry: Luxman incorporated thermal and overload protection into their designs, which helps safeguard the amplifier from damage due to overheating or short circuits.
6. Bias Adjustment: The amplifier’s class AB design requires precise biasing to ensure that transistors are operating in the optimal region to minimize crossover distortion without excessive heat.
Output power 55 Wrms @ 8 Ohms
Frequency response 8 Hz - 28 KHz (-1dB)
Input sensitivity 670 mV
Midband Gain 30.4 dB
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