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

Virtually all the amplifiers on the market are based on a push-pull symmetry model. The push-pull symmetry topology has no particular basis in nature.

Vacuum tubes and transistors don't either. This is a red herring.

I don't normally disagree with Nelson, but in this case I do. 

If physics is a part of nature, then we have an access to see that indeed, push pull does have a basis in nature. Two men with a large saw can cut down trees a lot faster than a single person can. You can see that analogies can be used in ways to make any argument you want 

We've been selling OTLs for the last 49 years. They have one stage of gain so are simpler than an SET which might have 3 gain stages including the output. 

So you can see there are a lot of ways to twist the simplicity argument around too. 

The bottom line is regardless of the amplifier class of operation or topology, the result must be musical, so that amplifier will have a very good first Watt as well as the succeeding Watts. 

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.

I can't describe better my experience with SET and push-pull amps. I personally prefer a natural bass of a SET than a push pull punchy bass. My set amplifier has a very high distortion (THD) but it sounds clearer than my push-pull and solid state amplifiers with much less THD. The comment made by Ralph somehow explains this phenomenon. 

So if you listen mainly listen to (an amplified) rock or electronic music, push-pull would be fine. But if you want to fully enjoy an acoustic music, you will do that better with a set amplifier.

It surprises me that the THD is still a major parameter for measuring the sound quality. It is quite irrelevant to the quality of the sound as we perceive it. Even the formula by which it is calculated doesn't look relevant. I guess the engineers were unable to develop  a more adequate parameter for measuring the sound quality so far. I suggest this is the only reason why THD still remains a standard. 

So if you listen mainly listen to (an amplified) rock or electronic music, push-pull would be fine. But if you want to fully enjoy an acoustic music, you will do that better with a set amplifier.

@niodari This statement is misleading at best. Electronics really don’t care what kind of music you play. An orchestra is acoustic and it can play as loud as a rock band and can have just as much bass energy.

I don’t regard THD as having much to do with sound quality. It is a metric that is only useful after the distortion spectrum has been analyzed. 

For example the harmonic spectrum of a typical SET is pretty good; imagine what that would be like if it was the same spectrum but a 10th as much at full power. Distortion obscures detail, so an amp of the latter distortion character would be more revealing at any power level and more relaxed. A good PP amp can do exactly that. 

When doing analysis of any amplifier, IME/IMO its a good idea to see what harmonics are showing up at low power, at 6dB below full power and then see how the amp behaves when overdriven. 

Its also a good idea to look at distortion (and its spectrum) not just at 1KHz, but at 20Hz and 5KHz also. Tube amplifiers often fall apart at lower frequencies (SETs in particular); you put in a sine wave but the output can look pretty dreadful. So 20Hz response really can tell a lot about an amp. 

At what frequency does the output fall off? If there is no feedback, phase shift will affect tonality and sound stage presentation to 1/10th or 10x the cutoff frequency, depending on which end of the audio band we’re talking about. 

From those measurements you can get a good idea of how musical the amp can be. 

The thing that isn’t being discussed here is the vast difference in power between the SET vs the PP amp used. If you really want to hear what that is about the SET should be the same power as the PP amp. For example if you have a stock Dynaco ST70 compared to a 35 Watt/channel SET, you’ll find out really quickly how the two actually compare. 

Since high power SETs are not easy to find and really expensive if you do find one, its a bit easier to try to find a PP amp of the same power as the SET. If you can do that again you find the SET has no musical merit over the PP amp, if both are built to good quality construction standards (often PP amps of low power are not given the same quality of parts as a 35 Watt amp might have). 

Alternatively you could compare an SET against a PP amp which uses the same tube complement, in particular the power tubes.

If one amp has feedback and the other does not that too is a tremendous variable!

It is on the account of these three variables that most comparisons between SETs and PP amps don’t hold water; they are instead examples of a logical fallacy known as a limited sample size.