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This is a fair ask, not a bargain: USD 175 sits close to the recent USD 162 median, comfortably within the typical USD 131–201 range. It is neither unusually cheap nor overpriced, so value depends heavily on whether the amplifier has been tested and operates cleanly.
The D-540 is a particularly appealing vintage integrated, with a lively, high-current design, useful MM/MC phono support, preamp/power-amp separation, and substantial dynamic headroom despite its rated 40 watts per channel. Its straightforward controls and capable phono stage make it more versatile than many period rivals. At this price, confirm both channels, inputs, speaker outputs, phono operation, controls, and the rear-panel pre/main jumpers; a clean, quiet example would be a sensible buy.
Independent perspective — not a price guarantee. Always verify condition, accessories and provenance before purchase.
Proton Electronic Industrial Co., Ltd. emerged from Taiwan in 1981, establishing its base in Banciao, Taipei-Hsien, as a manufacturer targeting the U.S. consumer audio market with high-quality components. Linked to Fulet Electrical, which produced notable NAD amplifiers, the brand launched around 1984 to expand into consumer electronics, including acclaimed TV monitors like the 600M and 602M models. By 2009, it remained active, building on a heritage of precision engineering from shared facilities with brands like NAD and Dynaco.
The company focused on premium hi-fi gear optimized for real-world performance, emphasizing tuners, receivers, amplifiers, and integrated systems that drove everyday loudspeakers with exceptional clarity. While not delving into headphones or cables, Proton's lineup prioritized robust playback under practical listening conditions, from radio reception to vinyl and cassette sources, earning praise for its engineering rigor in the 1980s.
Proton holds a solid reputation in vintage hi-fi circles as a mid-tier powerhouse, favored by collectors for its reliable, high-value sound that punched above its price point. Positioned as an accessible alternative to elite brands, it appeals to discerning buyers seeking durable, no-nonsense performers rather than boutique exotica, with ongoing interest in its schematics and restored units.
See all Proton listings on RADAR.
