Sansui AU 555 (1968-1973)

Name: Sansui AU 555
Brand: Sansui

At 10.5kg, it sits on the shelf like a promise kept—solid, serious, and ready to sing.

Overview

The Sansui AU 555 isn’t just another integrated amplifier from the late 1960s—it’s a cornerstone of the brand’s first generation of solid-state designs, marking Sansui’s confident leap from valve to transistor technology. Built to preserve the lush, musical character of its tube predecessors, the AU 555 was engineered with a clear philosophy: deliver high-fidelity performance without sacrificing warmth or presence. Owners report a sound that defies its era’s technical austerity—smooth midrange, rich bass, and a top end that sparkles without harshness. It wasn’t the most powerful amp on the block at 26 watts per channel into 8 ohms, but it was never about brute force. This was about balance, refinement, and a listening experience that felt more like a conversation than a demonstration.

Despite its modest power rating, the AU 555 was designed with serious engineering under the hood. The circuit topology relies on silicon transistors, including the now-notorious 2SC458, which collectors note are prone to degradation over time. The amplifier uses a quasi-complementary output stage and a single-supply design with capacitor coupling, a common but carefully implemented approach for the period. It features negative feedback across the board, contributing to its low distortion figure of 0.3%, and includes a two-stage differential amplifier in the voltage gain section. The preamp stage is shielded, as is the power supply, suggesting Sansui prioritized noise rejection and signal purity even in a mid-tier offering.

Physically, the AU 555 commands respect. It weighs in at 10.5kg and measures 420mm wide, 145mm high, and 310mm deep—substantial without being unwieldy. The chassis is housed in an attractive walnut cabinet, a touch of warmth in both looks and acoustics, while the front panel is all-business: an all-black metal faceplate with one-piece metal knobs that feel precise and durable. The layout is clean and functional, with clearly labeled inputs and controls, and the inclusion of pre-main connectors means owners can repurpose the unit as a standalone preamp or power amp—a flexibility that still impresses today.

Specifications

Manufacturer	Sansui Electric Co., Ltd.
Product Type	Solid state integrated amplifier
Year of Production	1968-1973
Output Power	26 watts per channel into 8Ω (stereo)
Frequency Response	20Hz to 20kHz
Total Harmonic Distortion	0.3%
Damping Factor	12
Input Sensitivity (Phono MM)	2.5mV
Input Sensitivity (Tuner, Aux)	150mV
Input Sensitivity (Mic)	3.5 mV
Signal to Noise Ratio (Phono)	70dB
Signal to Noise Ratio (Tuner, Aux)	90dB
Output (Line)	140mV
Speaker Load Impedance	4Ω to 16Ω
Semiconductors	22 x transistors, 6 x diodes, 4 x thermistors, 1 x SCR
Dimensions	420mm width, 145mm height, 310mm depth
Weight	10.5kg
Voltage	Multi-voltage capability (110V/120V/220V/240V selectable)

Key Features

Triple Tone Control Circuit with Independent Channel Adjustment

The AU 555 features a sophisticated triple tone control circuit that allows independent adjustment of bass, treble, and midrange frequencies—not just left/right balance, but full tonal shaping per channel. This level of control was uncommon in mid-priced integrated amplifiers of the era and reflects Sansui’s commitment to user customization. The circuit uses low-noise silicon transistors in an NF-type configuration, minimizing added noise while maintaining signal integrity. The tone controls are widely praised in owner reports for their musicality; they don’t just cut or boost—they shape the sound with a natural hand.

Pre-Main Connectors for System Flexibility

One of the more forward-thinking design choices was the inclusion of pre-main connectors, allowing the AU 555 to function as a standalone preamplifier or power amplifier. This modularity was rare in consumer-grade gear at the time and speaks to Sansui’s ambition to offer professional-grade flexibility. Owners who later upgraded their systems often repurposed the AU 555 as a preamp, appreciating its low-noise design and clean signal path. The separation of preamp and power supply sections, along with shielding, ensures minimal crosstalk and interference when used in split configurations.

Built-in Phono Equalizer and Dual Tape Monitor Loops

The amplifier includes a built-in phono equalizer for MM cartridges, requiring only 2.5mV of input sensitivity—well within range of most moving magnet pickups of the period. It also features two tape monitor loops, enabling users to switch between playback and recording sources seamlessly. The tape monitor function allows real-time monitoring of the recorded signal, a feature valued by audiophiles who recorded from vinyl or reel-to-reel. These inclusions made the AU 555 a true hub for analog systems, reducing the need for external processors.

Loudness Control, High/Low Filters, and Muting Circuit

The AU 555 is equipped with a loudness switch that applies a frequency-dependent boost at lower volumes, compensating for the ear’s reduced sensitivity to bass and treble when listening quietly. It also includes high and low filters—useful for cleaning up source material or matching speaker response. The muting switch attenuates output by 20dB across the full frequency range, a subtle but effective way to lower volume without adjusting the main control. These features, while not unique, are implemented with care and reflect a design ethos centered on usability and sonic refinement.

Historical Context

The AU 555 was part of Sansui’s pioneering first generation of solid-state integrated amplifiers, a series that included the AU-222, AU-777, and AU-999. These models were designed to carry forward the sonic legacy of Sansui’s successful valve amplifiers, particularly in terms of warmth and musicality. When introduced, the AU 555 represented a significant milestone: it was the first time a “truly professional control amplifier of Sansui quality” became available in the medium power price range. This positioning allowed audiophiles to access high-end performance without the premium price tag, helping to expand the high-fidelity market in the late 1960s.

Collectibility & Value

The Sansui AU 555 is regarded as a reliable and well-built amplifier from a formative period in solid-state audio. Its warm, engaging sound has earned it a loyal following, with some owners preferring it to contemporaries like the Marantz 2226. However, age has introduced common failure points: noisy or scratchy potentiometers (especially the volume control), failing electrolytic capacitors in the power supply and phono stage, and degradation of the 2SC458 transistors, which can lead to one-channel failure. Restoration typically involves a full recapping, thorough cleaning of controls with contact cleaner, and careful adjustment of DC offset and bias current. The service manual is available through archival sources, aiding in repairs. Market value varies significantly with condition; while raw units appear for a few hundred dollars, fully restored examples command higher prices—though specific USD valuations are not documented in the source material.