Would You Rather Own A Good SET Amp, Or A Great Push Pull Amp?

Ralph,

I also wanted to thank your for your always insightful and educational expertise. Your input on this topic is invaluable, and has me much closer to the direction to go in. Much appreciated, as always. 

I built SE amps for years--2A3, 300B, 845--because I could. ;-)  No feedback, no 'scope needed, just crasm in as many expensive parts as you could and eventually you could get pretty good sound.  But having developed the skills to build a really good PP amp, I'll never go back.  I'm with Ralph--a good 20-35 wpc PP amp can be a real joy.  I've settled into the Williamson design because if its tonal veracity.  For my money a moderately-powered Williamson gives you everything an SE amp offers plus a lot more in terms of bandwidth, speaker control and low distortion.

I think that it might depend on what you most find glorious in your listening.  I have owned several good to great PP amps; for many years I used the renaissance VAC 70/70, 2 parallel 300Bs per phase per side.  This amp did everything superbly well.  Eventually it needed TLC and yet more tubes (and a matched quad of good 300Bs is a bit painful) and I switched to the (SS) Pass XA 25.

The lure of tubes got me again and I have built a couple of Elekit SET amps.

The performance of the TU-8900 (with upgraded caps and OPTs) is utterly glorious, most of the time.  Its rendering of subtle details, at low volumes especially, makes one stop breathing so as not to interfere!  It does this in a way unmatched by the VAC amp.

The one technical advantage of a single ended design (or an SS amp) is that there are no OPT zero crossings.  Even in full class A, where the tubes are biased out of cut off during a complete cycle, the OPT is still at zero (given perfect channel matching) at signal zero.

I listen to a lot of chamber and choral liturgical music where the ability to reproduce ppp passages, and the decay of notes, superbly is a vital factor in my enjoyment.  The performance of full ffff orchestral tuttis is not on a par with a great pp amp, but note that my Rockport Atria speakers are rated at 87dB at 2.83v rms.

As I said above, I don't have a clear sense of which is inherently better.  I own very low-powered versions of SET and pushpull amps, but they are not comparable in design so I cannot draw any conclusion.  But, over the years I have made some general observations.  First, the very best sounding triode tubes are all quite low in output power (e.g., 45 and 2a3), and using them in SET topology means one must have highly efficient speakers or use them only to deliver modest listening levels.  By efficient, I mean something approaching or above 100 db/w with 8 ohm or higher nominal impedance).  Second, as Atmasphere noted above, they need an air-gapped output transformer to deal with saturation and one can only partially offset the loss of inductance by making the core massive.  This means the output transformer is usually very expensive; cheap SET amps with puny transformers sound whimpy to me.  

But, with proper speakers and a quality build, SET amps deliver a very "pure" sound that can be quite seductive.  While bass tends to be not as tight and punchy as that of a good pushpull amp, the bass has its own positive attributes--it has natural and subtle differences of tone while pushpull bass is much tighter and punchy at the cost of sounding a touch "mechanical" (sameness).  I have no disagreement with someone finding the balance of attributes favoring SET amps.  But, I do disagree with the "magic" qualities ascribed to SET amps; you can hear the same qualities in pushpull amps, perhaps not in the same balance, but there is nothing exclusive to SET sound.  

We have not even considered OTL amps in this discussion.  A well implemented OTL amp can have explosive dynamics and sound very vivid without being harsh or unpleasant as one might expect with that kind of dynamics.  

Per bass issues with SET. Over decades of using both pp and SET I've found bass performance to be highly variable. I've probably had more issues with overly resonant, one note bass with pp vs set. What I've discovered over the long term is speaker and amp has to be a sympathetic match, the right tool for the job. One needs both high efficient and impedance friendly speakers for SET, also need amp with quality power supply, meaning some reserve capacity, finally quality transformers. 845 SET can drive some speakers not often associated with SET, power supplies with these quite substantial, around 900V plate voltage with these. With the right speakers a nice 300B amp running top tier 300B tube like the new Western Electric is sublime, never heard any pp that can replicate harmonic structure of these.