Sansui AU 505

Ninety watts of IHF music power in a satin-black box that weighs less than a case of beer. Sansui's "best buy" integrated, built to embarrass amplifiers that cost more.

Overview

The spec sheet leads with 90 watts, and that's the number Sansui wanted you to see — but read the fine print and the AU 505 tells a more honest story. That 90W figure is IHF music power at 4Ω and 1,000Hz, measured one channel at a time. The continuous RMS ratings are where the real amplifier lives: 35/35W per channel into 4Ω, 25/25W into 8Ω, each channel driven. Drive both channels together into 8Ω and it settles at 23+23W at 1,000Hz, or 12W × 2 across the full 20 to 20,000Hz band at rated distortion. None of that is a scandal — it was standard mid-1970s specsmanship, and Sansui printed every one of those figures in the owner's manual rather than hiding them. It just means the AU 505 is a genuinely modest amplifier wearing a flattering suit.

What it does with those watts is the reason it still has a following. The manual describes an all-silicon transistor design, 23 transistors and 2 diodes in total, with low-noise silicon devices in the equalizer circuit and especially large-capacity transistors in the power stage. Distortion is quoted at less than 0.5% THD and less than 0.5% intermodulation distortion at rated output, both including the preamplifier. The IHF power bandwidth runs 25 to 40,000Hz, and the overall frequency response from AUX reaches 20 to 60,000Hz ±2dB. Damping factor is approximately 50 into an 8Ω load, which is respectable for the class and explains why the amp holds small speakers together better than its wattage suggests. Load impedance spans 4 to 16Ω.

The feature set is where the AU 505 earns its reputation for punching above its price. There's a front-panel DIN socket in addition to the usual rear pin jacks, so a cassette or open-reel deck can be patched in and out without crawling behind the rack. More expensive models of the period omitted it. A microphone jack sits on the front panel with a dedicated MIC position on the selector, and the manual notes that mic input appears centered between the two speaker systems regardless of the mode switch position. The Tuner Selector is a one-touch lever that lets the listener jump straight to radio reception mid-record or mid-microphone without touching the main selector. Two pairs of speakers can be connected and selected individually or together, using Sansui's one-touch button terminals, and the Power/Speakers switch has an SPKR OFF position for private headphone listening.

Tone shaping is more capable than the price point implies. Bass offers ±13dB at 50Hz, treble ±10dB at 10kHz, and the loudness contour adds +10dB at 50Hz and +8dB at 10,000Hz with the volume control backed off to -30dB. There are also switchable filters - a low filter cutting 10dB at 50Hz and a high filter cutting 10dB at 10kHz, both at 6dB per octave. Input sensitivity is 3mV into 50kΩ for phono, 4mV for mic, and 200mV for tuner, aux, and tape monitor. IHF hum and noise is quoted at better than 70dB for phono and mic, and better than 75dB for aux. Crosstalk is better than 50dB at rated output for both phono and aux.

The chassis measures 115mm high, 407mm wide, and 278mm deep, and weighs 8.0kg. Inside are an extra-large power transformer and an oversized heat sink. Sansui's own manual leans hard on both: the transformer is described as supplying ample power with minimal voltage fluctuation, and the heat sink as letting the output transistors run at full capacity for hours. Power consumption is rated at 70W with a 120W maximum, and the amplifier ships with voltage selection for 100, 117, 220, or 240V at 50/60Hz.

Sansui's advertising in Studio-Sound (September 1973, p.45) positioned the AU 505 plainly as "another best buy with some more power than the AU-101". That makes it a step up from the brand's entry-level integrated, not a flagship. It was a volume seller, not a halo product. The manual's own marketing copy says "no other integrated amplifier in its class can touch Sansui's AU-505 for tonal quality, versatility, ease of operation and economy", which is manufacturer advertising and reads like it.

For anyone servicing one today, the manual is unusually forthcoming. The rear panel carries a voltage selector behind a screwed-on name plate, resettable between 100/117V and 220/240V operation, with the fuse changing accordingly - 2.5-ampere glass-tube for 100/117V, 1.5-ampere for 220/240V. Sansui's warning against substituting a different capacity or a piece of wire is blunt. The parts list identifies the power transformer as a 400-A1040XX, the output devices as 2SD188 types in matched L and M grades on socketed mounts, and the volume control as a 250kΩ (B) dual-gang unit. Speaker output transistors sit in sockets rather than being soldered to the board, which makes a rebuild easier. The manual directs owners to a Sansui dealer or authorized service station for anything beyond routine maintenance.

The AU 505 was built to a price and it shows in the power figures, not in the layout. Two pairs of speaker terminals, a front DIN socket, a tuner selector, switchable filters, a properly specified phono stage, and a heat sink sized for continuous duty are not the features of a throwaway amplifier. The matching tuner in the lineup was the TU-505.

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