Sansui AU-20000
Seventeen pounds of transformer and a pair of meters that tell you exactly how hard you're pushing it.
Overview
The AU-20000 is an integrated stereo amplifier from Sansui Electric Co., Ltd. The service documentation calls it that and nothing more - just "INTEGRATED STEREO AMPLIFIER" on the cover of a manual written for the engineers who would keep these running. That fits. The unit was built to be serviced, adjusted and understood, and the documentation Sansui shipped with it assumes as much.
The headline number is 170 watts per channel minimum RMS, both channels driven, from 20 to 20,000 Hz into 8 ohms with no more than 0.05% total harmonic distortion. The same 170-watt figure holds into 4 ohms across the full 20-20,000 Hz band, and the amplifier will also drive 16-ohm loads at 85 watts per channel. At 1,000 Hz the numbers move up a little - 180 watts per channel into 8 ohms, 170 into 4. That tells you the power supply has real headroom and the rating doesn't collapse when the bandwidth widens. Frequency response at one watt is quoted at 10 to 50,000 Hz, +0/−1 dB. Intermodulation distortion, measured by the SMPTE method at a 4:1 ratio of 70 Hz to 7 kHz, is less than 0.05%. The manual lists 4-ohm operation at the same power as 8-ohm operation, which means the supply is built to deliver current, not just voltage.
Load handling needs some care. A single pair of speakers can be anything from 4 to 16 ohms. Connect two pairs at once and both must be 8 ohms or higher. Sansui's manual is blunt about this. It warns that a single speaker below 8 ohms in a four-speaker setup can take the amplifier down, and that two sub-8-ohm speakers in parallel act exactly as if the load were under 4 ohms. The front-panel speaker switch selects A, B, or A+B, and the rear terminals are arranged for straightforward left/right and plus/minus connection.
The metering is what sets the AU-20000 apart from most integrated amplifiers of its class. Two level meters on the front panel can be switched to read the output of the built-in power amplifier, giving a visual indication of RMS output against an 8-ohm reference. The manual explains the correction: with a 4-ohm load, a meter reading of 10 watts actually represents 20 watts, and with a 16-ohm load that same reading means 5 watts. You can watch power output without making a sound, which helps for setting levels before the stylus drops, checking headroom on a demanding passage, or confirming that a cartridge is overloading the phono stage. Sansui even suggests using the meters together with the 40 dB meter function to catch cartridges that produce unexpectedly high output on hotly-cut records, and to step the input sensitivity selector from 1.5 mV to 3 mV or 3 mV to 6 mV when the meters push past zero.
That input sensitivity switch affects both PHONO-1 and PHONO-2. The PHONO-1 circuit also adds a pickup load selector with 50 kilohms as the normal setting and 30 and 100 kilohm alternatives. It works as a subtle high-frequency response trim, so the owner can voice the phono stage instead of taking what the factory picked. Moving-coil users running a step-up head amplifier can set sensitivity to match the head amp's output instead. Hum and noise figures are better than 70 dB on both phono inputs, better than 80 dB across tuner, aux, and all three tape playback inputs, and better than 100 dB on MAIN IN. There are three tape loops, with output level at 1,000 Hz quoted for TAPE-1, 2, and 3 REC via pin jacks.
The tone section is three-band with defeat. Bass offers ±10 dB at 30 Hz, midrange ±5 dB at 1 kHz, and treble ±10 dB at 20 kHz. The manual says to push the tone button IN before adjusting, and to keep the DEFEAT button engaged at all other times so the entire tone circuit is separated from the amplifier proper, wherever the controls sit. Filtering runs on two axes. A low filter has 20 Hz and 40 Hz cutoff positions at 12 dB per octave for hum, rumble, and warped or off-center records. A high filter at 7 kHz or 12 kHz handles scratchy vinyl, FM stereo hiss, and tape noise. There's also a muting switch offering −10 dB for ordinary listening rooms and −30 dB for late-night sessions. The manual pitches it as a way to get finer latitude from the volume control as much as a convenience for when the telephone rings.
Audio (October 1976, p.46) listed the AU-20000 among Sansui's amplifier offerings in its annual equipment directory, and HiFI-Stereo (1978, p.54) covered the model's place in the lineup alongside stablemates like the AU-9900 and AU-717. The AU-9900 is an 80 W/ch design with 10-50,000 Hz response at one watt. Against that company, the AU-20000 sat at the top of Sansui's integrated range: more than double the power of the AU-9900, three tape loops instead of two, and metering that the lower models didn't offer. The AU-11000, at 110 W/ch, was the next step down. Collectors comparing the three generally treat the AU-20000 as the line's flagship integrated.
Practical ownership notes come mostly from the manual itself. The unit is heavy, the transformer is large, and the design assumes a service engineer will eventually open it. The service manual exists so technicians can "repair, adjust, maintain and order the replacement parts" correctly, and it insists on the stock numbers and parts names from the parts lists rather than generic substitutes. The documentation recommends grounding the chassis to reduce hum during record playback and noise during AM reception, and it addresses grounding the unit together with other components in the system. Connecting a tuner involves matching its output level to the phono level so program sources don't need a volume adjustment every time the selector moves.
Documented collector market data for the AU-20000 is thin. There is no reliable sales history to quote, no established price range, and no consensus on which specific components fail first with age. Anyone considering one should treat it as a restoration candidate by default. A 170-watt integrated amplifier of this vintage with three tape loops and a configurable phono stage is worth the effort, but the effort is real. The manual is available, which helps a lot. Outside its own factory documentation, the record on this model is sparse.
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