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Some interesting/controversial statements here re: SET's


jimjimbo

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Good read and generally accurate with regard to SET amps themselves. And the comments on horn speakers are well, colored in themselves. But the subject comments itself is very similar to how I think. I have given thought to divulging my tube amp inventory to just one KT88 SET integrated (the KT88/66 among several other tube types purported to be single ended, as they are not true triodes) but after another listen to the George Wright 2a3 monoblocks has me re-thinking this. While there is a lot to be said for Class A solid stae single ended Nelson Pass designs there is that "something"  a 2a3 provides that is hard to reproduce with solid state. And it is this "something" that  push-pull and Ultralinear tubes leave me rather ho-hum.

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I found that with many reviewers they have no idea what they are talking about technically. I just want to clear up some bad information regarding push pull amps.  The author makes it sound like you physically cut the signal in half into "plus and minus'" and then "recombine" them. Eh, that's not how it works, it's an AC signal, there is no plus or minus as it alternates hence the name. A push pull amp instead will make a mirror image of the signal that is 180 degrees out of phase, so at any point in time one signal is in it's positive phase while the other is in it's negative phase, the potential between the two phases is greater just like your house power, you measure from any phase to neutral you get 120v but measure phase to phase you get 240v. If you are trying to get more power to the speaker instead of having one tube swing 800v on the primary you have two tubes that swing 400v out of phase which will give you 800v. Having a push pull amp does not automatically mean you have crossover distortion, it can be run Class A which means no active device goes into cut-off; i.e. all devcies conduct current the full 360 degrees of the input waveform. A single ended amp has to conduct the full waveform so naturally it's going to be Class A. Crossover distortion is when an amp runs into Class B operation and one of the devices is in cut-off (non conducting) for longer than half the cycle (greater than 180 degrees), this will give a little notch at the zero crossing henc the name crossover distortion. The issue with push pull amps is the non-linearities naturally inherent with the devices and circuits won't exactly be the same for both phases, so they will never be an exact "mirror image".

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I stopped reading after this point:

 

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To get the magic from an SET amp, you have to mate it with a very high-efficiency speaker, at least around 95 dB or higher--and the speaker can't have any nasty low-impedance curves in its design.

 

The transducers in an audio system are by far the limiting factor for performance. Why in the world would we limit the speaker design to something that is compatible with the SET amp?

 

That's like saying...."I like square wheels, so let's design all the roads so that my square wheels give me a smooth ride"

 

I have no problem with square wheels and funny roads, just as I have no problem with SET amps and have even appreciated some of the incredible midrange detail. I just think the thought process for preferring SET is a bit odd. Why not just embrace it for what it is, rather than call on some odd nostalgia philosophy thing?

 

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1 hour ago, alzinski said:

Having a push pull amp does not automatically mean you have crossover distortion, it can be run Class A which means no active device goes into cut-off; i.e. all devcies conduct current the full 360 degrees of the input waveform.

A great many newer push-pull amp will operate in class A up to a certain point.  Since most of us have Klipsch, it is easy to stay in the Class A operation of a push-pull amp.

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Yes a perfectly balanced push pull amp is symmetrical which produces  odd harmonics (for that stage only, it won't cancel anything before it). Lke I said before it will never be perfectly balanced  (exact mirror images of each other) so there will still be some even harmonics but they will be much lower than a typical single endeds stage.

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