Pass Labs INT 60 VS. Primaluna Dialogue Premium HP VS. Arcam A49

As almarg mentioned, the high output impedance of some tube amps is what would concern me. 

One one of my biggest audio disappointments was getting a 60 watt tube integrated that I came to find out had on unusually high output impedance. My speakers had 12" woofers and a low impedance of 3.2ohms. The amp could not do anything with that woofer. I had nothing but mids and highs and very weak lower mids and bass.

Now, I had a sixteen watt SET 845 tube amp from Art Audio that ran those same speakers beautifully; some of the best sound I have had. To this day I can't get the sound of that amp out of my head. It was fantastic and I wish I still had it.

I guess the takeaway from this would be try before you buy if you can. It could be fantastic or it could break your heart.

Cheers,

Scott

Sumac,
Yes, this is why I am such an advocate of the listening experience  (when possible). Very likely that the 16 watt SET amplifier has better quality power supply and output transformer than the 60 watt tube amplifier.  

Also very likely that the SET Art Audio would be considered a poor match for your speakers if judged solely on specifications. With the failure of the 60 watt amplifier what led you to try the subsequently sucessful SET? I happen to find measurements and specifications useful as a screening mechanism  but know they aren't capable of revealing the entire story as your experience confirms.  But you have to begin somewhere and listening isn't always an option before purchasing. 
Charles 

@charles1dad

It was a long time ago when I was just getting into the audiophile hobby thing (actually, I didn’t even know I was getting into it, I was just looking for a great sounding system).

I did just what I wouldn’t advise anyone to do. I bought it without hearing it. One of my favorite reviewers, the late John Potis, wrote an outstanding review on the the Art Audio Carissa. John was one of the best. He had a great ear and could describe the sound of gear beautifully.

http://http//www.6moons.com/audioreviews/artaudio2/carissa.html


Your right, it had a big stout power supply. The 60 watt integrated came from a very high end tube amp manufacture and should have had a great power supply and been outstanding as well. But it bit me in the backside hard.

The Carissa is one piece of gear I wish I could get back.

Cheers,

Scott

John Potts as you say was a very good reviwer.  He had the ability to effectively discover and describe the essence of an audio component. I always enjoyed reading his work. I recall reading his reviews of Art Audio and Canary  amplifiers ago. 
Charles 

Scott, thanks for your inputs. Here is a corrected link to Mr. Potis’ review of the Carissa:

http://www.6moons.com/audioreviews/artaudio2/carissa.html

Interestingly, it is described in the review as being a "no negative feedback" design, but having an output impedance of 1.2 ohms, which is on the low side for a zero negative feedback SET design. While at least in its present version it is described at the Art Audio UK site as incorporating 9 db of feedback, which is a substantial amount, that would tend to reduce output impedance significantly. Both references, however, indicate that maximum power capability has been sacrificed somewhat in order to "double available current" in comparison with traditional designs.

All of these indications (1.2 ohms output impedance, 9 db of feedback, doubled current capability) are consistent with low output impedance, certainly in comparison with most SET designs, and in comparison with JA’s measurements of the PL Dialogue Premium, and I suspect also in comparison with the PL Dialogue Premium HP. (I would assume that the reference to a 10 ohm output impedance that is provided at the Art Audio UK website refers to optimal load impedance, rather than to amplifier output impedance).

In contrast, the interaction of an "unusually high output impedance," such as Scott described for his former 60 watt tube integrated, and a speaker impedance that is low in the bass region and higher at other frequencies, will produce exactly the results he described ("very weak lower mids and bass"), compared to the results most well designed solid state amps (and many other tube amps) would have provided.

BTW, I was one of those who suggested caution regarding the Cary tube amplifier in the thread Charles referred to. I did note in my post in that thread, however, that the output impedance of the Cary amp was unspecified, as was the corresponding damping factor (damping factor and output impedance are inversely proportional), and that measurements of those parameters did not appear to be available.

Also BTW, in saying all of this I’ll add that like several of those who have posted above I personally am firmly in the category of being a fan of tube power amps. But I am also not a risk-taker when it comes to questionable pairings.

Best regards,
-- Al