Does Sansui AU-7900 drive difficult load speakers better than higher specced amplifiers?

[Kreshna]

Okay, this is about my B&W DM302, whose impedance drops to 3 ohms from 200 to 300 Hz, and to 5 ohms between 10 to 20 kHz. When driven by 25 wpc Sansui A-40 (not the best of Sansui, apparently), the resulting sound is strained and shouty. Very fatiguing.

B&W DM302's impedance curve, compared to that of JBL L20T.

My B&W DM302s, driven by 25 wpc Sansui A-40.

Then I changed the amplifier to 95 wpc Yamaha RX-V663 AV receiver. Yes, it is AVR watts, but I only use two of the AVR's seven channels, because I was using Pure Direct stereo mode. When driven by the significantly more powerful Yamaha RX-V663 (compared to Sansui A-40), the strain reduces significantly and the sound quality gets better. The strain and the shoutiness only return in loud volumes.

The B&W DM302s, driven by Yamaha RX-V663 internal power amplifier.

Then I finally added a Rotel RB-985 five channel power amplifier to the audio chain, using the Yamaha RX-V663 as preamp and volume control. The Rotel, being a dedicated power amplifer, has apparently 5x100 honest wpc. Again, I only used two of the Rotel's seven channels. The sound is no longer straining nor shouty, not even at loud volumes.

The B&W DM302s, driven by Yamaha RX-V663 internal power amplifier.

So I guess B&W DM302, being a difficult load, needs sufficiently powerful amplifier to sound good. With 25 wpc Sansui A-40, everything sound shouty and strained. With 95 wpc Yamaha RX-V663 (typical AVR wpc?), the strain and shoutiness only appear in loud volumes. With 100 wpc Rotel RB-985 (which seems to be more honest wpc), the strain and shoutiness completely disappear.

Except in one song: I Want U by Basement Jaxx.

It doesn't matter which amplifier I'm using to drive the B&W DM302s, the song I Want U always sound strained and shouty. Yes, even on Rotel RB-985. I thought it was the song, until I changed the B&W DM302s into easier-to-drive JBL L20Ts. And then the song doesn't sound strained and shouty anymore.

Recently, my previously damaged Sansui AU-7900 has been repaired and restored. Out of curiosity, I tried it to drive the B&W DM302s. And the result is very surprising.

First, the song I Want U doesn't sound strained anymore. Second, every song I play sounds very laid back, warm, polite, and very effortless, even more so than Rotel RB-985. In fact, everything sounds way too laid back, too polite, too effortless, and too relaxed that it becomes boring in the long run. When driven by Sansui A-40, B&W DM302s give me severe listening fatigue because the sound is shouty and strained. When driven by Sansui AU-7900, it's the opposite; I could literally listen to the B&Ws for hours due to the effortless, totally non-fatiguing sound. However, the resulting sound is way too polite for my taste. Heck, even my baby daughter didn't wake up from her sleep when I pumped up the volume on this song.

What surprises me is Sansui AU-7900 doesn't seem to be specced as high current amplifier. High current amplifiers' power output usually doubles down to lower impedance, like 75 wpc at 8 ohms and 150 wpc at 4 ohms, while Sansui AU-7900's power output is not described as such.

So, why does Sansui AU-7900 drives difficult load speakers more effortlessly than the supposedly more powerful Rotel RB-985? Does the AU-7900 drive low impedance better than higher specced amplifiers? Or is it all just coincidence?

 

[darkblue94]

It's a mystery wrapped in an enigma with a sauce of conundrum drizzled on top.

 

[nj pheonix]

There certainly are enough balls in the air here to make drawing an accurate conclusion not easy.
First the lower powered piece just might not have enough current to drive the low impedance.
Amps sound different (I'm sure it can be debated but generally the consensus IMO)
If I understand correctly, you're using the same piece for preamp in all the scenarios?
If so it takes a variable out of the equation. If not preamps can sound different too.
There's something to be said for system synergy.
Some pieces just seem to work better together than others (for no easily explainable reason).
Easy peasy, see?
I'm not sure how current FTC ratings are enforced. I'm sort of a believer that watts is watts (RMS both channels driven, in the case of a 5 channel amp, they may derate it at 5 channel output

 

[KentTeffeteller]

B&W speakers are usually not efficient nor easy to drive, and they tend to tell the truth about what is fed to them as far as your sources and music and room are concerned. Most Sansui amplifiers are not what I'd drive B&W speakers with. They need something which handles their often low impedance loads, and their need for high power.

 

[audiotemp]

I was asked recently to help a friend having similar issues with a 100W/ch Rotel stereo receiver and B&W 2-way speakers. The receiver labeling indicates that 4 Ohm speakers are acceptable but no power output rating into that impedance is given. The speakers being used have an 8 Ohms nominal rating but have a 3 Ohm minimum, similar to your 302's. This set-up worked well for the owner for 10+ years but has started giving problems recently whenever bass-heavy source material is played.

At present I am suspecting decreased power supply performance in the amp (due to age, heat, etc.) may be the issue. That's still a guess, though, since I don't have the amp in-hand to work with directly. My point, though, is that when you are pushing an amp towards its limits then age and condition of the amp may be a factor.

I'm curious as to whether the power supply was re-capped in whatever restoration was done to your AU-7900.

 

[Kreshna]

Well, the listening room and position are not changed. And yes, the AU-7900 is restored to the original spec. I have listened it using my usual JBL titanium domed speakers and the sound doesn't change.

I just don't expect the AU-7900 would drive B&W DM302 more effortlessly than Rotel RB-985. Absolutely no strain at all. Everyrhing sounds very laid-back, very relaxed.

 

[Bahamayellow]

My Sansui G-8000 specs out at 120 watts at 8 ohms and 4 ohms. It doesn’t double down like traditional amps. I looked up the spec on the AU and it lists 8 ohms only. I’m not an expert on those models also. There are some Sansui models that handle a 4 ohm load better. I’m not sure which ones but you could post this in the Sansui forum also. I have m & k s100b that are 4 ohm speakers and my G series drives them with ease. If your looking for a more modern sound Sansui the G series to me has that. I know that Au model you have is a good one maybe just not for those speakers.

 

[Kreshna]

My Sansui G-8000 specs out at 120 watts at 8 ohms and 4 ohms. It doesn’t double down like traditional amps. I looked up the spec on the AU and it lists 8 ohms only. I’m not an expert on those models also. There are some Sansui models that handle a 4 ohm load better. I’m not sure which ones but you could post this in the Sansui forum also. I have m & k s100b that are 4 ohm speakers and my G series drives them with ease. If your looking for a more modern sound Sansui the G series to me has that. I know that Au model you have is a good one maybe just not for those speakers.

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Indeed.

I've been using B&W DM302s with Sansui AU-7900 on a couple of days, and I haven't heard any strain nor shoutiness. In fact, the entire sound is very tame that my baby daughter doesn't wake up from her sleep when I pump up the volume.

Anyway, how would you describe "modern Sansui sound"?

 

[Bahamayellow]

Hello it sounds like the Au 7900 might have a very warm sound like my Sansui 7000 which almost sounds warm and tube like. The sound in the G series is not really tame it’s fast and accurate. Similar sound to something made in the 90s or modern sound.

 

[Kreshna]

Hello it sounds like the Au 7900 might have a very warm sound like my Sansui 7000 which almost sounds warm and tube like. The sound in the G series is not really tame it’s fast and accurate. Similar sound to something made in the 90s or modern sound.

I see... No wonder Sansui AU-7900 sounds really beautiful with JBL titanium domed loudspeakers; it seems the tube-like sound matches well with the allegedly harsh-sounding metal dome tweeters. The AU-7900 also works well with NHT SuperZero, making the treble sound cleaner and airier.

It sounds too polite with B&W DM302 though. The treble sounds rolled-off while the midrange sounds recessed, that my wife said the B&W DM302 sounded muddy compared to the NHT SuperZero the AU-7900 previously drove.

Of course, the DM302 sounding polite (and perhaps muddy) is a totally new experience to me, because the speakers sound strained, totally impolite, and really shouty with other, less-capable amplifiers.

 

[Zekeman]

Old thread I know, but I have owned and restored perhaps 50-60 7900’s and have never experienced a laid back sound characteristic with any of them. Did you ever draw any conclusions on this issue?