So, you have tested them?
If that's the case, you will be very much aware that the SA-9800 cannot deliver much more than 130 watts per channel into 4 ohms without triggering the OC protection and that causes all sorts of horrible clipping characteristics (ie the amplifier is heavily current limited- something all decent designs did away with in the late 70s), whereas the A-91D will hit nearly 250 watts in the same conditions with no current limiting. Not only that, the A-91D will approach 350 watts per channel into a 2 ohm load, all without shutting down.
The main reason for the poor performance of the SA-9800 was Pioneer used 120w 12A RETs (essentially a multi transistor IC on a die) and only two per rail (a total of 4 for each amp)- not anywhere near enough for 4 ohm operation at high power. RETs lose their linearity with age, hot spotting issues cause gain mismatches etc. I used to have a jar full of dead MT200 RETs. The SA-9800 would have blown up if driven hard into 4 ohms- so they current limited it for the same rated power at 8 and 4 ohms.
The A-91D is also ruler flat at full power, whereas the SA-9800 is not- its power bandwidth is actually pretty poor with a pronounced roll-off at high powers. I don't know why, because the RETs have a 60MHz ft, but all the ones I have tested exhibited the same rolloff to be a few dB down at 20kHz at anything over 80watts. The 1 watt response is ruler flat.
The A-91D also uses a way more advanced NSAIII whereas the old SA-9800 is their first iteration and considerably less stable. Pioneer refined NSA into a DIP solution which is about 100 times more reliable than the discrete version in the SA-9800.
Build quality isn't even close. All the knobs on the A-91D are solid, the only solid knob on the SA-9800 is the volume control- all the rest are aluminium over plastic- cheap.
The SA-9800 also cooks itself via its regulated supply, like many other brilliantly designed Pioneers of the late 1970s when cost cutting had hit and good design went out the window for a while. Yep, place a high dissipation linear regulator under everything with no airflow. Genius. The phono stage is lovely sounding and better than the A-91D, but unreliable, prone to DC drift offset issues and is usually noisy due to the FETs which are notorious trouble makers.
The PCM56P selection K twin 4xOS DAC is a lovely performing onboard DAC too with a Yamaha digital filter, beautifully implemented and a very nice addition on the A-91D.
Personally, I think the blue Futaba VFDs look tacky and cheap, especially with the painted silver plastic escutcheon glued to the front panel around them on the 9800. I too loved them, but that was back in the 1970s- when they were new (I loved my first CTF-900 I bought secondhand in 1985), the more segments the better back then, but there is nothing classy about them now. They just look old- like most of us I guess.
I've fixed enough SA-9800s over the years and not even one A-91D has ever been on my bench for actual repairs (probably because it cost $2799 new in Australia and not many were sold). That being said, I have done some preventative work on a few A-91Ds with speaker relays and replacement gas filled input relays.
I always pick up Pioneer silver gear because it's fun to fix but I always get rid of it because the late 80s TOTL gear from just about any brand was and is much better.
The 1980s and into the early nineties offered us incredibly good TOTL hifi gear- way better than the TOTL gear in the 1970s. It was just very expensive and not a lot was sold as compared to the glory years of the 70s. Much of it is still in the hands of the original purchasers because it was so reliable, so there is less for us blokes to 'scroe'.
In the very late 1980s/early 90s, we would sell 1 piece of TOTL gear for every 200 pieces of the rest of the range- maybe more. That was Pioneer and Yamaha. I never sold an A-91D. I (personally, not the shop total) sold a few M90/C90 combos. I sold maybe two A-777s. I probably sold 100 A-400s. I sold a pile of VSX-D1ss dolby flagship receivers- laser disc was big then!
I remember selling two or three pairs of NS-1000X speakers (at $5k pr), one CDX-10000 (at $12,000), lots of NS-700Xs and heaps of 100x, 30x and 5x speakers from Yamaha. Yamaha's CX and MX amps were an easy sell because they were powerful (on paper), big and had big red power meters and were remarkably cheap. 40 something blokes wanted a big black box that made lots of bang for their bucks and Pioneer looked way too classy for them.
I just wish people would stop pretending the 1970s was the pinnacle of all things hifi. I wish it was (because I've got an awful lot of 70s gear), but it simply isn't.
Rant over.
I own both those amplifiers (100% up to spec). They're both side by side in my stacks. Often,I have listened/compared both via high quality CDP's including Naim CD5 with Chord Cobra III interconnects. Both sound very familiar (someone else also agreed with me on this in another unrelated thread). To say the A-91 D sounds better than the SA-9800 is false in my opinion...but each to he's/her own.
They're both excellent sounding amps that share the same sound signature...oh,and I personally prefer the looks of SA-9800 what with it's beautiful fluoroscan meters.
