Onkyo TX-555
Forty watts that behave like fifty, wrapped in a pale-gold casting that still looks like money.
Overview
The first thing you notice on the TX-555 is the front panel. It's a heavy pale-gold-anodized casting with solid end-cap posts, and it looks considerably more expensive than the receiver's price tag ever suggested (Audio, October 1972, p.29). Onkyo's own advertising of the period pushed the same point, promising unmistakable excellence in craftsmanship and materials. The reviewer led with the chassis before the circuit.
The TX-555 is an AM/FM stereo receiver rated at 40 watts continuous per channel into 8-ohm loads with both channels driven, at 0.3% total harmonic distortion. Onkyo's advertising of the period billed it alongside the TX-666 as part of its Solid State receiver line, with the TX-555 specified at 2.0 µV FM sensitivity (HiFi-Stereo, October 1972, p.97). On paper that's a mid-pack number for its moment. The amplifier section, though, was rated conservatively. Measured THD hovered just over 0.1% all the way up to the rated 40 watts per channel, and the unit didn't reach its claimed 0.3% until each channel was producing 46 watts. Intermodulation distortion stayed under 0.1% up to roughly 30 watts and only hit the rated 0.4% at 49 watts per channel.
The power bandwidth claim was understated too. Onkyo published 15 Hz to 35,000 Hz, but bench testing found the amplifier held rated power from 10 Hz out to 40 kHz. The headline frequency response runs 10 Hz to 35,000 Hz within ±1 dB, and the magazine's own sweep of the full signal path, tone stages included, stretched from 9 Hz to over 30 kHz inside that same 1 dB window. Damping factor is listed as over 100, which keeps a firm grip on acoustic-suspension speakers.
The phono stage is the best part of this receiver. Input sensitivity is 2.5 mV with a claimed 200 mV overload ceiling, and the measured overload point came in at 225 mV, above spec. That means dynamically cut records won't clip the input, whatever cartridge is on the tonearm. RIAA equalization is held to ±0.5 dB. Phono hum and noise measured 60 dB below full output referenced to a 2.5 mV signal (66 dB when referenced to a more typical 5 mV input), and the Aux input ran 75 dB below rated output. The magazine's listening panel found the phono mode the receiver's strongest suit, with transient response that handled their most dynamic discs without audible overload or breakup.
The tuner section is competent rather than spectacular, and the period review is candid about the trade-offs. IHF sensitivity is 2.0 µV with a 70 dB signal-to-noise ratio, 1.5 dB capture ratio, 75 dB selectivity, 50 dB AM suppression, and 40 dB stereo separation at 400 Hz. The review logged 45 stations with good quieting and clean distortion performance, but flagged a high stereo threshold. Distant stations broadcasting in stereo were received in mono, and the field-strength meter showed 25 µV on the strongest of them. It takes more than 30 µV to trip the stereo decoder. With a decent antenna and typical signal strengths that's a non-issue; at the fringes of the dial it's a real limitation. The magazine also noted that the measured sensitivity and separation figures, while lower than the "super tuners" of the day, didn't translate into a listening penalty.
Inside, the amplifier uses differential and direct-coupled circuitry with ASO protection circuits, according to Onkyo's own advertising of the period (Audio, October 1972, p.29). The tone controls offer ±10 dB of bass at 100 Hz and ±10 dB of treble at 10,000 Hz. The loudness control compensates both frequency extremes with a moderate treble lift. The tone, filter, and loudness action was found to conform to the manufacturer's claims and standard practice. Controls were reported smooth and easy to use, with volume tracking accurate to below −60 dB from full volume, which matters at late-night listening levels.
The receiver measures 18⅜ inches wide, 5½ inches high, and 15⅜ inches deep, and weighs 28 pounds. Power draw is listed at 250 watts maximum from a 120 VAC, 60 Hz supply. The original price was $399.95, though Onkyo's advertising through late 1972 and early 1973 variously billed the TX-555 at $349.95 alongside the step-up TX-666 at $429.95, with a three-year parts and two-year labor guarantee (Audio, October 1972, p.29; High Fidelity, December 1972, p.93). Treat the pricing as a range. The $399.95 figure appears in the formal equipment profile, while the lower figure shows up in the company's own promotional copy. The review closed by calling the TX-555 good value for anyone shopping in the 40-plus-watt-per-channel class.
That same review pointed buyers toward the TX-666 for better FM performance and 50 watts per channel, with the caveat that if the higher-powered set was as conservatively rated as the TX-555, both deserved serious consideration in their respective classes. The TX-555 is not the flagship, but it's a well-built mid-market receiver whose measured performance consistently outran its published specs. Buyers should expect the usual age-related service. The review makes no mention of failure modes, and no reliability record is documented here. Audio gave it a clean bill of health on the bench and in the listening room.
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