I had a friend interested in this integrated amplifier, the Sansui AU-9500 and I passed it off as yet another mediocre amplifier of the era.  But my knee-jerk reaction to it was kind of bugging me so I did a little more research on this baby and even examined the circuit topology from the schematics (Circuit topology, why less is more).

Upon further investigation, this looks to be one of the best integrated amps the era offered and quite possibly the best integrated amp Sansui ever produced, hence the strong following.   This amplifier was released when the owner and founder of Sansui (Khosaku Kikuchi) was on a quest to offer the best solid state amps in the world and this was his “no holds barred” TOTL (top of the line) flagship integrated model.  In that respect it is a brilliant piece of audio history, probably why my friend was so drawn to it.

This amplifier was released from 1972 to 1973 only, and Khosaku Kikuchi subsequently retired in 1974.  Although circuit design may have progressed in later Sansui integrated amps, it remains highly doubtful that sonic qualities improved, especially if such circuit designs implemented high negative feedback loops in the “THD wars” of the time (The THD wars. Why lower distortion often doesn’t equal better sound quality).  In fact, the rather high THD of .1% on this model actually bodes well for its musicality and sonic potential.  I doubt they subsequently made an integrated amp with better build and/or sound quality.  And Khosaku Kikuchi’s goal to make solid state sound like tubes was certainly an admirable one, though that wasn’t really realized until the MOSFET amps of the early 80s came out, with the exception of the high slew rate/low TIM Audionics of Oregon CC-2 driving certain speakers (The Audionics of Oregon CC-2. More distortion, more better.).

The Japanese and US approach has traditionally been polar opposite in regard to the “less is more” or “more is more” approach, and Sansui obviously believes that by adding more tone controls you can achieve better sound quality.  Hence the elaborate tone controls on the AU-9500, while US designers were going the opposite direction.  Of course which is better is purely subjective, as are all things high-end audio.  I am of the later camp and prefer not to have any tone controls at all, even just the usual “bass” and “treble” (Why I prefer analog preamplifiers that lack tone controls), which is the main reason I choose the Nak CA-5A (The Nakamichi CA-5A preamplifier) over the Nak CA-5A II.  I’ve always found graphic equalizers, that became so popular in the late 70s, to be flashy tone suckers.  But once again that’s just one guy’s subjective opinion.

It’s worthy to note that Japanese owned and operated Nakamichi contracted an American (Nelson Pass) as a hired gun for their circuit designs when they endeavoured to provide the world with the best amplifiers of the era in the early to mid 1980s, following their huge success in the cassette tape business.  His circuit designs have always been extraordinarily simple, so that’s an indisputable indicator of where the chips ultimately fell, as are nearly all the modern high-end audio components that followed.  I consider the Nakamichi amplifiers designed by Nelson Pass to be the best of both worlds from that era – fantastic circuit topology combined with Japanese build quality and stunning industrial design (The Nakamichi PA-7 power amplifier).

So the main concern I would have in regard to the Sansui AU-9500 would not be in regard to sound quality or its ability to drive just about any speakers desired, but rather due to its age combined with its complexity combined with the difficulty of finding places to get it competently serviced and it’s weight to ship.  I would consider it a roll of the dice and while it may run another 40 years, I seriously doubt it.

As a side note the AU-9500’s direct coupled design is a rather bold move, indicative of their emphasis on utmost sound quality at that time.  What it means is that without DC servo protection to shut things down in the event of a DC power fault feeding the speakers, it will destroy them in very short order.  It probably has a DC servo  protection circuit somewhere, but I couldn’t locate it on the schematics.  The direct coupled design omits DC filter capacitors on the output stage due to their potential to adversely effect sound quality, which I find ironic given the proliferation of what I consider to be unnecessary circuitry in the circuit design to begin with.

I initially had concerns about the early 70s AU-9500 possibly being behind the design curve that came in the late 70s.  But as previously noted, the high THD figure, coupled with the fact that they even mentioned TIM distortion in their specs, tells me that they were “on it” (in a good way) and trying hard to avoid that “first-generation transistor sound”, which makes sense as it was one of their stated objectives, to have a “tube-like” sound.  I found this interesting since I thought Robert Sickler at Audionics of Oregon was one of the first amplifier designers to look at how negative feedback adversely effects sound quality and strove for high slew rate (What is “Slew Rate” and why does it matter?…)/low TIM distortion amplifier designs.  The entire industry followed his lead, but maybe he was just one of the first American amplifier designers to look at it.  Robert Sickler was also onto MOSFETs way before their time, but Nelson Pass later picked up that ball and ran with it to great effect.