SET v. Pushpull


I did a search and didn't find any threads on this topic.  I am a newbie to tubes - I have a Tavish Adagio phono stage, and I am looking to add an integrated tube amp into the analog chain in my system - I have never owned one, so my knowledge level is low.  Right now I am running KEF LS50 speakers, but they are a little small for my listening area so possibly looking at larger speakers - I was very impressed by the Joseph Audio Pulsars I recently heard, as one example.

Anyway, most of the integrated tube amps in my price range are seem to be push pull, although the Line Magnetic is SET.  At a high level, I understand the push pull design gives higher output power than SET, but also higher potential for distortion.  

Any practical experience with the pros and cons of each?  And how important is this in the overall scheme, in real world applications?  Say, compared to the choice of output tube?

Thanks,


Tom 
tgr

Showing 1 response by atmasphere

So much depends on topology!
*Some* pushpull amps have crossover distortion problems but most do not. What push pull amps often do have trouble with is the so-called 'first watt'. Many do have higher distortions in that area, but its usually not crossover distortion, although that is often what gets trotted out as the explanation.
SETs have a distortion character where as the power level is decreased, the distortion linearly decreased to unmeasurable. Some push-pull amps are like that too- ours are, and in general I would suspect any fully differential push-pull amplifier to have a similar quality if designed correctly.
SETs often do not employ loop negative feedback! This accounts for both their high distortion at full power and also their higher output impedance. The tradeoff is that first watt- which tends to have lower distortion on this account. That can be done with push pull amps too, but it is trickier.
Generally speaking, a sensitivity or efficiency of a loudspeaker that is less than 85 db is bordering on criminal- it gets nearly impossible to find an amplifier that simultaneously makes enough power and actually sounds like music in most average rooms. Exceptions might be if the speaker is only heard nearfield (within 3-5 feet) or the room is quite small. You just wind up having to push the amplifier too hard, and in the case of an SET this really won't bring out the strengths of the amplifier!
Someone already mentioned my comments about SET amplifier power above so I won't repeat them. But here's a thing in a nutshell:Tube amplifier power whether SET or not is expensive so its to your amplifier investment dollar's advantage to use a speaker that is more efficient and easy to drive. In particular its to your advantage to avoid four ohm loads as all amplifiers (tube, solid state or class D) make more audible (and unpleasant) distortion into lower impedances! If high quality reproduction is your goal, again your amplifier investment dollar is best served by a higher impedance (8 ohms or more) loudspeaker. If sound pressure is your goal you have a 3db argument for going with 4 ohms, only you have solid state.