Overview

The Sansui AU-111 Vintage is a 40W+40W tube integrated amplifier released in 1965. Known as one of the flagship models manufactured by Sansui Electric during its golden period, it features a push-pull circuit using four 6L6GC tubes and Sansui’s proprietary SW-50 output transformer. Re-released as the AU-111 Vintage in 1999, it remains highly popular in the used market as one of Japan’s representative vintage audio equipment pieces.

Scientific Validity

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The AU-111’s measured values are clearly insufficient by modern standards. THD 0.8% (at 40W) significantly exceeds the transparent level of 0.01%, causing audible distortion. The S/N ratio of 70dB (MM) falls far short of the transparent level of 105dB. While the frequency response of 20Hz-50kHz (+1/-1dB) appears good, this is merely standard for tube amplifiers and cannot match the ±0.1dB or better achieved by modern digital amplifiers. Channel separation of 45dB (MM) does not reach the transparent level of -70dB or better, indicating insufficient acoustic separation performance. Compared to the transparent reproduction achieved by the latest digital amplifiers with THD+N 0.001%, SNR 120dB, and frequency response ±0.05dB, the scientific validity is extremely low.

Technology Level

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While advanced for 1965, it rates below average by current technical standards. The 6L6GC tube plate voltage setting of 485V and Sansui’s proprietary SW-50 output transformer were excellent for their time, but equivalent performance can now be achieved with smaller, lighter, and more efficient technology. The multi-stage negative feedback circuit for full-band flat characteristics offers no technical advantage compared to modern digital signal processing or Class D amplifier technology. While the tube circuit design itself is meticulous, it represents a fundamentally inefficient and complex design approach from the perspective of modern semiconductor and DSP technology.

Cost-Performance

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Current used market prices range from 250,000-350,000 JPY depending on condition, evaluated here at 300,000 JPY. The Fosi Audio V3 (13,600 JPY, Amazon Japan price) exists with equivalent or superior functionality and performance. The V3 achieves 300W+300W maximum output, THD+N 0.003%, SNR 110dB, and frequency response 20Hz-40kHz (±0.5dB), significantly surpassing all AU-111 measurements. Cost-performance calculation: 13,600 JPY ÷ 300,000 JPY = 0.045, rounded to 0.1. Including tube replacement costs, power consumption (approximately 200W vs 60W), and maintenance expenses, the V3 is overwhelmingly superior in operational costs. Excluding vintage value, the pure performance-to-price ratio is extremely disadvantageous.

Reliability & Support

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Being over 50 years old in design, component aging and parts availability present serious problems. Tube life is short at approximately 5,000-10,000 hours, with replacement 6L6GC tubes costing 5,000-15,000 JPY each. Electrolytic capacitor degradation creates high risk of sound quality deterioration and failure, with overhauls requiring 100,000-300,000 JPY. Sansui no longer exists, providing zero manufacturer support. The number of technicians capable of repairs is declining, making maintenance costs and technical risks extremely high. However, information sharing within audio enthusiast communities is active, with abundant repair information and modification examples available.

Rationality of Design Philosophy

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The design philosophy of acoustic reproduction using tube circuits is irrational from a modern scientific perspective. Tubes inherently possess defects of high distortion, low efficiency, high heat generation, and short lifespan - problems completely solved by modern semiconductor technology. The design consuming 200W to produce 40W output is inefficient regarding environmental impact and cost. The 25kg chassis weight is unnecessary when modern amplifiers achieve equivalent performance at 1/10th the weight or less. Design philosophy dependent on subjective values like “warm sound” without measurable sound quality improvement effects is meaningless from a scientific acoustic engineering perspective. However, it was a rational design choice under the technological constraints of 1965.

Advice

Those considering purchase should make decisions after fully understanding objective performance evaluation. In measured performance, the 13,600 JPY Fosi Audio V3 surpasses the AU-111 in all aspects. The 300,000 JPY price is purely based on antique value, not compensation for acoustic performance. For practical purposes, modern Class D amplifiers are strongly recommended. Even if tube amplifiers are desired, modern designs like the Linear Tube Audio ZOTL40 Mk.II (5,800 USD, approximately 870,000 JPY) offer far superior actual performance despite higher prices. The AU-111 is suitable only for those prioritizing historical value and collectibility, or for tube circuit learning purposes. For practical use prioritizing sound quality, modern product selection based on scientific evidence is strongly recommended.

(2025.7.21)