I don't know where to put this, so I'll put it here -- Nelson Pass revisits "Leaving Class A"

Ilusndweller

Junior Member
His class AB amps sure do sound great and crystal clear SUPER LOUD and clearly out of class A territory. At least the Adcom 535, Forte Model 3, and Nak TA-4A do. My ears (and system) are not nearly good enough to detect transitions between class A and B.
 

adaug

Senior Member
yeah. all i know is that i tend to like the sound of class a amps. and i like the sound of tube amps - there may be some correlation.

much of what NP wrote there went a bit over my head, but i think he was saying that an AB amp will have some A going on at all times - and its never going to be doing pure B. so yeah picking the AB bits out from the simultaneous A is going to be hard for anyone probably.
 

JohnVF

Administrator
Staff member
I got more of that then I thought I would. I don't really share the opinion on Class A, at least as a generalization. I think some Class A amps sound better than Some Class A/B amps, especially, maybe most especially, older Class A/B amps. I think some modern A/B solid state amps can sound better than some vintage Class A amps...depending on which amp it is of course. And even better than some modern Class-A amps. Wow, I've even managed to confuse myself here. I'll just say..it depends on which amp, more than whether its Class A or Class AB, to my ears. I do love my Pass Aleph 30, though. Its just that the added oomph from my modern 180wpc AB outweighs the sonic benefit the lower wattage 30wpc Aleph brings to the table with my speakers. If I had to pick, I'd not pick the Aleph (for these speakers). On my Quads, the Aleph sounds better so?
 

adaug

Senior Member
seems that class A amps will generally involve more care in matching with speakers (due to lower power) than AB amps. the good news is that efficient speakers that are a match for tube amps will tend to be match for class A amps.

outside of the pass-related ones, are there even very many class A amps on the market currently? the low power ratings, high heat production and high power consumption seem to make them a very niche thing, right?
 

JohnVF

Administrator
Staff member
seems that class A amps will generally involve more care in matching with speakers (due to lower power) than AB amps. the good news is that efficient speakers that are a match for tube amps will tend to be match for class A amps.

outside of the pass-related ones, are there even very many class A amps on the market currently? the low power ratings, high heat production and high power consumption seem to make them a very niche thing, right?
Luxman has made quite a few really nice ones over the years, and they continue to do so. I have a wonderful little vintage Sony one in addition to the pass.
 

MikeyFresh

Moderator
Staff member
the low power ratings, high heat production and high power consumption seem to make them a very niche thing, right?
Yes they are, but in addition to those various Luxman models over the years cited by @JohnVF , there are others from Accuphase, Krell, the lesser known but legendary in some circles BEL (Brown Electronic Labs), or the grandaddy of them all, the very first commercially available Class A transistor amps by Sugden, those are in continuous production since 1967.
 

fiddlefye

Senior Member
Nicely set out explanation. I haven't had much experience with Class A amps apart from running a couple of Yamaha integrateds in that mode and hearing them elsewhere. I did have a Krell here for awhile years ago, but it didn't particularly float my boat and made more heat than the tube amp it was meant to replace.
 

MikeyFresh

Moderator
Staff member
I did have a Krell here for awhile years ago, but it didn't particularly float my boat and made more heat than the tube amp it was meant to replace.
That is certainly a real drawback, and in this day and age, so too is the way in which these Class A amps will spin your electric meter. Not exactly in the category of "green".
 

fiddlefye

Senior Member
That is certainly a real drawback, and in this day and age, so too is the way in which these Class A amps will spin your electric meter. Not exactly in the category of "green".
Neither are my tube amps, but somehow it doesn't bother me as much. ;) The impetus for going Class A SS at the time was annoyance with a long, bad run with output tubes. Then I found Gold Lion KT-77s and the problem went away.
 
I have three Pioneer M-22. I usually run them on the tweeters and midranges. Right now since I am in a construction phase I have one running full range and it does sound great. But they DO put out a lot of heat. These are rated at 25-30 watts but don't clip till 50. Two or three hundred watts of heat output. Nice in the winter.

I heard a BUNCH of class D amp systems at Axpona and I have to say if they didn't tell me they were class D I never would have guessed. That was one of the reasons I went too. The Hypex amps have been around for 15 years and now Icepower and all the others. They couldn't POSSIBLY sound as good as class A could they. Well they sounded pretty darn good to me.

In one of the big ballrooms they had a whole wall of power amps with 8 KT 88 in each. I went over and looked and the room was about 20 degrees warmer on that side.

If you have a low power class A amp it is good to run it as a tweeter amp in a multi way system. (sorry I just can't stay off the soapbox on that subject 🙄)

Class A solid state might be somewhat more reliable than various tube amps but all that heat can and does toast a lot of components.

Today I was at a guys warehouse and he had pallets of Crown CTS series amps. Class D, Switchmode Power supplies. VERY green, built in "drive rack" DSP. VERY tempting.
 
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adaug

Senior Member
Class A solid state might be somewhat more reliable than various tube amps but all that heat can and does toast a lot of components.
yeah and there is another drawback or potential drawback to class A. they run hot outside, and just how hot is it inside? if you or anyone have experience with apparently premature component burnout in class A amps, please post.

with the long production cycle, it would be interesting to get sugden's take on this issue.
 

JohnVF

Administrator
Staff member
Bedini made some fine sounding Class A amps. Still great sounding if you can find one that hasn’t overly suffered from heat damage. A buddy of mine who’s been a rep for audio companies and has had his pick of basically anything, runs a Bedini 25/25 that’s been meticulously rebuilt. It’s a fine sounding amp.
 
My Pioneers have had one failure, a speaker relay. Not bad since 1976. Probably after about ten years. You can see evidence of the heat on the circuit boards. I think they did pay a lot of attention to thermal design. The chasis is massive cast aluminum , big heat sinks and vertical air channels. You can touch them after they have been on , without getting burned so that means the temp is like 110 degrees Fahrenheit. That is actually nothing for electronic components which are easy to purchase rated at 100 degrees C (212 F) or even 200 C.

Tubes contain the heat in a vacuum bottle which acts somewhat like a thermos. There is the phenomenon of "red plate" if they are biased wrong, but bias being off can happen to any amp tube or ss.

Even in non class A solid state amps there are often incidences of resistors and semiconductors cooking due to being too small/underrated.
 
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