SET vs Class A vs tubes vs Class AB amps


Long time reader, first time poster here. Can someone describe the basic differences in sound between a Class A amp , an SET amp, a Class AB and a regular tube amp? Are there basic sound differences in the general sense? I have only owned Class AB amps.
needlebrush
All well-designed amplifiers (low output impedance, adequate slew rate and current delivery, low harmonic and IM distortion) operated below clipping will sound alike - Peter Walker of Quad fame.
I don't think that the class of an amp is universally descriptive of the entire genre, except for SET's which are so power limited that they require a whole different class of speaker.

I've heard Class A amps I liked, and some I didn't.

Best,
E
I like my SEP lower powered amp, as it simply sounds far better than any other amp I've used in my current (or previous) system, possibly because Dennis Had knows how to design a brilliant amp that I can afford (I saved over 50 grand by not buying a Kondo Audio Note with similar output)...I'm evaluating a "Continuity sort of Class A" Schiit Aegir (also relatively low powered) that so far has shown some interesting tonal characteristics, and might earn a place in my amp collection...it has to pass a background test and be vetted by a committee before taking an oath...takes time. So far I still prefer my SEP, and yeah, you do get chained to a "different class" of speaker where high efficiency is paramount...my current main speakers are supposedly 99db efficient, but I've had good luck with a 90db or so pair as well...it's just nice to have more headroom from efficiency.
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@wolf_garcia 

Interested in your experience with Dennis Had amp. Is there a thread/post you could point me to?

Horacio
All SET amps are class A by nature.  In a class A amplifier, the output devices are biased on for the entire waveform.  This is why they are lower power output when compared to similarly sized class A/B amps.  Some of the best amps we've heard are class A, but it's really about the overall design and build.  Plenty of fantastic A/B and other output type units out there.  
All are great if done right.
Lewinskih01/Horatio...on the Audio Aficionado site there are hundreds of pages devoted to all aspects of Dennis Had amps. That site can keep you busy for hours and make your head spin with the "what power tubes with what rectifier with what input tube" endless discussions. Fun stuff.
I have two amps. A 300b SET from AncientAudio and the 12R (solid state) from Bakoon. They sound more similar than different.
As mentioned by pretty much all posters above it depends on the designer how the amplifier is going to sound and its advantages or disadvantages. The ultimate goal is to power the speaker comfortable with more power in reserve than the speakers will need and not to impart a sound coloration onto the music.
The more important issue is a total system synergy where all the components work well with each other. Component matching to the size of your room, your taste in music and preferred listening volume.
I think you might find the Sanders white paper on Tubes vs. Transistors to be educational.  Look for sanderssoundsystems.com or something like that. 
You want to seek a good sounding amp, and unless you have difficult speakers to drive, the type is irrelevant.

I have two systems with Class A, one with AB and one with tubes.
I couldn’t agree more that one of the most, if not the most consideration is system synergy to your tastes, and less about type/class.  An additional important factor is what type genre of music you listen to and what is the source.  For me, SET tubes deliver the best tone for voices, either analog or digital.  But it falls way short on delivering the goods through dynamic passages or rock, where a couple of different Class A classics are my choice. If digital, my best sound is delivered with tubes all the way through- SET if light voices, tube PP (monoblocks) if other. If vinyl, I lean to solid-state amps behind my 28 tube Aesthetix IO Sig phono unless it is a single guitar or similar.  I too have a multitude of options when it comes to amps- SET, SEP, PP with tubes, Class A, A/B solid state, mosfet, Bipolar, SIT, etc., etc.  and all that is somewhat irrelevant, my decisions are based on the sound.  Yesterday I did a listening session where I biamped two BEL 1001’s in stereo (one amp channel driving the base, the other the mid/treble, one dedicated to each speaker) vs the 1001’s bridged in Monoblock.  Big difference, not necessarily better, but different. The biamped implementation was warmer with a bit more meat on the bones vs the bridged implementation which had a much wider and deeper soundstage- I preferred the bridged mode.  I am starting a shootout where I am going to compare and contrast three classic Class A amps.  Stay tuned.
It's bass, not base. My little SEP Dennis Had tube amp will play anything well...from chamber jazz to Little Feat to Mahler...as any well designed amp should. If your rig is "music style specific" there's simply something wrong with the thing...don't expect much low end from tiny inefficient monitors, or relative loudness from a 2 watt amp, but otherwise don't be denied! My latest amp experiment is a Schiit Aegir...so far it's brilliant...cost less than my cables.
Hi Wolf-Garcia-

1) got autocorrected. Yes, bass, sorry I missed it.
2) Thanks for your thoughts, but I don’t agree with your premise, but I’m glad you are happy with your system. Things are so system and component specific that is is hard to sometimes understand why someone prefers one system tone to another.  But, a general subjective statement that I think is more often accurate than not is that if you took a common audiophile system and swapped in a <25 watt, 2 volt input sensitivity amp, like the Inspire, most would be happy at nominal listening levels but disappointed at higher levels.
i think it is like the trade-off I feel with Magnepans.  I had three different models for 20 years and was ecstatic with the imaging and speed.  However, compared to a dynamic speaker, their bass is lacking- I’m sure some will argue this, but most agree that Magnepans are a bit lacking in the bottom. And to put a 10-20 or 30 watt amp as the drivers would be really disappointing.
I’m looking for extraordinary realism, sometimes at fairly high SPL’s. I’ve found that some of the less powerful tube amps and less sensitive amps in general have challenges in my system with analog. I owned a Dennis had Inspire amp for 18 months, pretty good on voice and mid/treble, but in my system, lacks bottom end with only 18 watts and a fairly low input sensitivity ( probably around 2 volts but Dennis doesn’t publish its sensitivity.  A BEDINI by comparison is .5v input sensitivity). BTW- speakers are Von Schweikert’s- 93db Efficient and 6 ohm.  I have found that for me, input sensitivity is important because I am using a pure tube phono stage (up to 80db gain) and a zero gain line stage.  So listening to vinyl, sensitivity is critical in my kit, which is not “simply something wrong”, just a preference and trade off I have as nothing- as in nothing- I have heard in any system to date- delivers the realism of my Benz-VPI- Vibraplane-Aesthetix-Truth front end.  I’m know I could add a line stage with gain or a SUT or a solid-state phono amp or listen to digital to “fix” my system and allow a lower powered amp to perform at a louder level without sonic degradation, but overall the tone and sonics would suffer for it.  
In addition, comparing a Bedini 25/25 with a 100/100 (same design and sensitivity 25 watts vs 100 watts) both sound pretty much the same at lower SPL’s and less demanding passages, but at some point the 25 clips and runs out of oomph before the 100. I’m not a head banger, both amps are well designed and play things well to a point. For me, in my fairly highly resolved system with many dependencies, the low power amps are really good on some things but not everything. realize not everyone shares my bias or preference, nor wants to deal with the overhead, but I can say that I am happy where I landed.
 Great stuff, shared with knowledge and respect , thanks . I ran a Modwright KWI 200 and JBL 4312A’s or Klipsch Heresy II’s with a sub. I then ran a vintage Marantz or a Sansui 9090 with the same speakers ( on 26” Sound Anchors ). Now I’m running a Had Inspire , Rogue Pre , Schiit Yiggy , Thorens TD 160, Zu Omens . I have a large supply on new and NOS tubes for the Had ( probably twice the amps price ). I love the Had -Zu pairing , but it’s VERY LIMITED . Low to moderate volume and quiet nights make for very intimate listening . It’s kind of like giant headphones . At  higher volume it’s irritating . Being a SEP it’s easy and forgiving . It’s also cheaper and little more powerful than a SET is. Bass is subject to which power tubes I run. But I have a sub I can turn on . As you can see, I’m a mid fi guy and cost driven . If you want to listen to Rush from another room , this is not for you . If you like clear vocals and strings this system is great . At modest levels even classic rock sounds good . My best advise is to audition different types of equipment. My next venture will be to incorporate a SS amp of 50-100 wpc into my system. So I’ll have to find something that’s not Too Dry . It’s all about the pairing and what sound you want . Happy Hunting , Mike . 
Thank you all for your opinions and advice, much appreciated!
Although the Schiit Aegir stood up well in its shoot-out with my little Firebottle HO SEP amp, it ultimately lost and sadly was sent home to Schiit. Nice try though and it clearly is a great design, but the Had digs deeper, sounds more like real music to my ears, and simply reinforces my preference for glowing tubes.