Onkyo MX-5 (1986–1988)

Name: Onkyo MX5
Brand: Onkyo

A 22.5 kg power amplifier that cares a lot about headroom and will put your speakers to work.

Overview

The Onkyo MX-5 is a stereo power amplifier. It was produced from 1986 to 1988 and launched in Japan at ¥148,000. This is a solid-state heavyweight, and it came out when integrated amplifiers were the default choice for most listeners. The MX-5 was for people who wanted separate amplification for genuine high-fidelity performance.

It weighs 22.5 kg and measures 455 x 191 x 437 mm, so nobody rearranges it casually on a shelf. The mass comes from the transformer and power supply capacity inside.

The MX-5 has a signal-to-noise ratio of 120dB (IHF A). That puts it in the company of modern high-end amplification. The damping factor is 100, which gives firm control over woofer motion and keeps the bass tight rather than loose and boomy.

The power output is where the documentation gets murky. Most sources agree on 100W per channel into 8 ohms. E-Waste Alchemy lists 100W per channel (8Ω, 20Hz-20kHz, 0.03% THD), and Art of Vintage confirms 2 x 100W RMS (8Ω). But conflicting figures exist: Vintage Audio Museum claims 2x40W/8 ohm, Amp Database says 2 x 60W / 8 Ohm, and Hi-fi Archive goes as high as 150 watts per channel into 8 ohms. Given the weight and the 330W power consumption figure from Amp Database, the 100W rating appears most credible. The 40W and 60W figures likely reflect measurement at different bandwidths or conditions, and the 150W claim seems optimistic.

At 4 ohms, the MX-5 reportedly delivers 100W + 100W (4Ω, 1kHz, THD 0.4%). Yahoo! Auctions documentation gives a rated output of 130W + 130W under the same conditions.

Frequency response claims vary by source. Blackdog Electronics, Art of Vintage, and E-Waste Alchemy all cite 5Hz-100kHz, while Yahoo! Auctions lists 10Hz - 100kHz (+0 -3dB). The broader figures reflect the amplifier's wideband capability, since extending well beyond the audible range helps stability and linearity within it. Vintage Audio Museum's more conservative 20Hz-20kHz figure likely represents the guaranteed specification rather than the measured capability.

The most detailed distortion data comes from Yahoo! Auctions: 0.004% at 1kHz, 8Ω, 1W; 0.02% at 1kHz, 8Ω, 40W; and 0.03% across 20Hz-20kHz at 8Ω, 40W. Multiple other sources confirm 0.03% as the headline THD figure. These numbers are respectable for the era, not state-of-the-art. The Vintage Audio Museum figure of less than 0.05% is the most conservative.

Input sensitivity is rated at 1V / 47kΩ for 50W output into 8Ω per Yahoo! Auctions. That is a standard sensitivity, so the MX-5 pairs well with most preamplifiers of the period. A 2V output from a typical preamp would drive it to full output with room to spare. The 47kΩ input impedance is an easy load for any source component.

The MX-5's physical dimensions vary between sources. Vintage Audio Museum and Amp Database list 424x148x372 mm and 10.2 kg. The majority of sources (Yahoo! Auctions, London Sound, Blackdog Electronics, Art of Vintage, E-Waste Alchemy) agree on 455 x 191 x 437 mm and 22.5 kg. The heavier figure fits the power output claims and the 330W power consumption. A 10.2 kg amplifier delivering 100W per channel would need remarkably compact power supply engineering, so the 22.5 kg figure appears far more credible.

Original pricing in Japan was ¥148,000 including tax, though Vintage Audio Museum lists a figure of 63,000 Japanese Yen, likely reflecting a different market or a later price reduction. In the Japanese domestic market of 1986, the MX-5 sat in the upper-middle tier of separate power amplifiers.

The MX-5's legacy is that of a serious, no-nonsense power amplifier from a period when Japanese manufacturers were at the height of their engineering confidence. It wasn't flashy, it didn't promise miracles, and it didn't need to — it simply delivered clean, controlled power with the kind of build quality that has allowed many units to survive in working condition to this day. For collectors seeking a Japanese power amplifier from the late 1980s that won't require a second mortgage, the MX-5 represents a compelling proposition — if you can find one.

One note for prospective buyers: the MX-5 is a power amplifier only. It requires a separate preamplifier or an integrated unit with pre-out connections. This simplicity is part of its charm — fewer circuits in the signal path means fewer opportunities for coloration or noise.

Condition matters a lot on an amplifier of this vintage. Units that have been well-maintained, with clean internal dust, healthy capacitors and no signs of heat damage, should perform well for years.

The MX-5 may not have the name recognition of some of its more famous contemporaries, but among those who know, it's respected as a genuinely capable performer. It delivers the goods where it matters — clean power, low noise, and the kind of build quality that makes vintage Japanese audio so beloved. For the right listener, it's a hidden gem worth seeking out.