Overview

The Lo-D HMA-9500mkII is a stereo power amplifier manufactured by Hitachi from 1980 to 1984. The original HMA-9500, released in 1977, holds historical significance as the “world’s first power amplifier using power MOS FETs.” The mkII version was sold at a high price of 270,000 yen at the time and was claimed to excel in high-frequency characteristics and linearity. Its circuit featured a simple 3-stage DC amplifier design, eliminating coupling capacitors to pursue faithful signal reproduction.

Scientific Validity

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Compared to modern measurement standards, this product’s scientific validity is extremely low. While specific measurement data is limited, it is impossible for this 1980s analog design to meet modern transparency-level standards (THD below 0.01%, S/N ratio above 105dB). The power MOS FET technology, though advanced for its time, falls far short of the measured performance achieved by modern Class D amplifiers. Its frequency response of around ±1dB does not meet the modern ±0.5dB standard and can introduce audible deviations. Inherent aging degradation of analog circuits also contributes to performance decline.

Technology Level

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While the historical significance of being the first to adopt power MOS FETs is acknowledged, its technological advantages are completely lost by today’s standards. The 2SK134/2SJ49 power MOS FETs boasted high-speed response, but this offers no special advantage in modern, well-engineered amplifiers. The 3-stage circuit and DC amplifier configuration, while rational for their time, are undeniably obsolete compared to more sophisticated modern amplification techniques. Overall, it represents an implementation within the technological limits of the 1980s, making it difficult to find any noteworthy technical value today.

Cost-Performance

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Against the current used market price of approximately 110,000 yen, modern amplifiers with comprehensively superior performance exist at a fraction of the cost. For example, the Fosi Audio V3 (approx. 20,999 yen) boasts higher output and incomparably better measured performance, such as a THD+N below 0.005% and an SNR above 110dB. The cost-performance calculation is “20,999 yen ÷ 110,000 yen ≈ 0.19,” resulting in an extremely low score of 0.2 after rounding. Excluding its vintage appeal, its pure performance-to-price ratio is not even in the same league as modern products.

Reliability & Support

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As a product manufactured in the 1980s, manufacturer support has completely ended. Acquiring necessary specialized parts, especially the power MOS FETs, is hopeless. Components like electrolytic capacitors, now over 40 years old, are subject to unavoidable degradation and could fail at any moment. Technicians capable of repairing it are extremely rare, making maintenance very difficult. With no warranty, the risk of post-purchase failure is exceptionally high.

Rationality of Design Philosophy

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The design philosophy, once considered advanced, reveals many irrational aspects from a modern perspective. The pursuit of sound quality through analog circuitry has been replaced by digital signal processing, which offers higher performance at a lower cost. The large, heavy chassis is the antithesis of modern compact and high-efficiency design. In an era where a smartphone and a high-performance USB-DAC can easily achieve equivalent or better performance, the rationale for a large, dedicated amplifier like this has been almost entirely lost.

Advice

The Lo-D HMA-9500mkII is a product with value as a historical milestone, but it cannot be recommended for today’s audiophiles seeking pure sound quality and performance. By choosing a modern Class D amplifier like the Fosi Audio V3 for around 20,000 yen, you will get an experience that is overwhelmingly superior in measured performance, reliability, and functionality. If you consider buying it for collection purposes, you must be fully prepared for high maintenance costs and the constant risk of failure. For building a modern listening environment, you should turn your attention to more rational and higher-performing alternatives.

(2025.7.21)