Looking for a class A low watt power amp recommendation

I have an older Nelson Pass design - the Forte 1A which depending on how it is biased will run up to 50W Class A. They are also great value on the S/H market. However, when compared directly to my Line Magnetic SET ( 16W ), I prefer the SET by some margin. The speakers I use at the moment are rated around 92 db/w. I notice you use Monitor Audio Silver 8 which are rated around 90/db. I see Stereophile tested them and the lab results gave around 88.5 db/2. Too low for most SET amps. Personally I have always found Marantz gear a little underwhelming. I have not heard the F series Pass amps but you would need more efficient speakers to get the benefit from their design. Class A designs in general produce much less distortion at lower power. As has been stated Class A generally amps produce a lot of heat and have a big power draw.

 

Usually they are. This one has huge transformers, plus some other ways I can't remember now to squeeze a whopping 15 WPC out of 300 B's. As I said, it's a venerable US maker, not a "designed in Britain - made in China" mongrel, so, I tend to take it it face value.

Look up the specs for Cary Audio CAD - 300SEI

 

I have relatively high efficiency speakers that are easy to drive 99 db/w and nominal 8 ohm impedance). I own a pushpull 45 tube amp, a parallel 2A3 SET amp and a pushpull 349 amp. The 2A3 amp has the highest power rating (6.5 watts). All of these amps sound really good in my system. The only solid state amp that I have really liked in my system is the First Watt J2 (borrowed from a friend). I have also heard his DIY-build SIT amp that is based on First Watt schematics.

I have heard some of the low-powered amps mentioned here. I like the Line Magnetic SET amps; they are decent for the money and just lack a little bit in the way of not being quite as lively and dynamic as the very best amps. The Cary 300 SEI sounded a bit too mushy and slow for my taste with the tubes it came with, but, putting in better tubes turned it into a quite decent 300B amp. I heard it with some very good 6sn7s and with Western Electric 300B and Kron 300B tubes and it was a much better amp. But, I actually hope that the 15 watt rating is a wild exaggeration; if it were really built to push tubes anywhere near that kind of dissipation, the output tubes would not last very long.

I have heard good and bad amps of all types so I don't think it matters if is class A or not. The OP is looking for something reasonably priced, which means Class AB or Class D are the most likely types in the running.

 

OK, I know I'm being nitpicky here, but these amps don't "run in class A then switch over to class AB." The definition of class AB is that it is class A at lower power and class B at higher power points. Both of the above examples are class AB amps. The OP specifically asked for class A in the title, so neither qualify in that regard.

I feel it is more than adequate to suggest he consider a high bias class AB, because it will stay in class A up to whatever point you want to make, like 20% of rated power, or 10W, for example. But to say it switches to class AB from A is a contradictory statement and doesn't make technical sense.

 

Pass Labs XA30.8. With efficient speakers, one of the best amps I've ever heard.

 

It doesn't work that way. Some amps are class A designs, some are class B, some are class AB (most of the audio amps today), and some are indeed class A/AB which is a real thing. There are other classes such as class C, class D, class G, class H, etc. The trouble here seems to be distinguishing between a class A and a class A/AB, then also a class AB and a class B. Class AB amps do not operate exactly as class B amps. In a class B amp, the bias current at the transistors is shut off completely with each 180 phase swing cycle of the AC signal. That allows the amp to run cool and produce a lot of power, but it also creates a lot of distortion. The distortion is at the crossover point, where the transistors cut off and back on again. In a class AB design, this crossover point is never completely off, there is always just a bit of bias and so current is allowed to flow as the cycle swings to the other phase, practically eliminating the crossover distortion. In a class A design, both phases of the signal are always conducting and so there is not any discernible amount of crossover distortion as full power is available continually. In a class A/AB design, the amplifier is allowed to operate in class A up to a certain, predetermined point and then it switches to class AB. It does not exhibit any of the class B distortion levels at crossover and is lower than that of a class AB as it can operate much of the time in pure class A without any switching. Since this is a much more gradual transition from one phase to the other , it is often referred to as a "sliding" bias rather than a switching bias arrangement.
Here's a little homework for the non-believers: Amplifier Classes and the Classification of Amplifiers
-Bill

 

KT88, you might want to read the link you provided. It supports exactly what I said.

 

You must have lost your way around the crossover point.
Have a look at this:

The article doesn't go into detail about A/AB but that info can be found on any site where Nelson Pass has been.
-Bill

 

I have a high end DIY build of a First Watt Aleph J design. I also have a First Watt M2. Both are nice amps.

But I wouldn't be holding my breath in hopes of finding a SIT-2.

 

Musical Fidelity has historically made Class A amps. Always kinda wanted an A100. Heard they worked great as heaters.

 

I don't think I got lost around the crossover point. And, that chart is exactly what I'd reference to clarify my point. Perhaps you have a bit of difficulty interpreting charts (insert appropriate smilie here)?

 

Yes, that is being nit picky. What word do you prefer instead of "switch" for the point where the power requirement exceeds the class A bias and the amp starts running in AB? Here's a list I came up with: switches, transitions, moves, goes, changes, transfers.

And as for the Cairn KO2, there is a physical switch which allows the amp to runs in class A only and never ??? into A/B. Or you can use the button to have the amp run 100 watts AB after it exceeds the class A rating.

 

Emotiva used to offer a SS amp that did exactly the same thing.

 

A runs full out all the time. No switching.

 

That's a beauty, or maybe it's just me.

 

As far as I understand, you can still get them new for $5K.

 

Done forgot about Sugden, folks ?

D.D.

 

You sure can!

 

Man I would love a Sugden piece.

 

^ Curious Helom, how long did you run the amp and did you run it the same length of time yesterday as the other days? 40% sounds like a lot but it could definitely be accurate. I'm just wondering how many hours of use it would take to hit that figure.

I have had the complete opposite experience. Got a Sugden integrated and while it certainly runs hot it has a lot more juice than the A/B integrateds that I've tried. It plays louder and cleaner than any of those other amps did. The sound was so different than what I was used to that it definitely took a bit of adjustment but now I can't go back. It just sounds more real and immediate to me. It will be Class A ss and/or tubes for me from now on. At only 21 watts (I think that's the number) and only a little larger than most ss integrateds under 100 watts, it's a very easy amp to live with. I agree with getting speakers that are easy to drive and using a lower wattage Class A amp (that Coda looks awesome though - if one has the money and space I could definitely understand getting something like that). For most of us, practicality will be a factor.

 

I only ran it for one day, maybe 5 hours, in addition to a couple idling hours. The day before, I ran my Yamaha for a good 3 or 4 hours in addition to it being at idle for at least 8. Nothing else was out of the norm, so the amp is the only culprit I can figure. Not very scientific but enough to give me pause with that amp.

 

I've heard good things about Sugden amps.

 

Sugden does make a big monoblock for those so inclined. Their stuff sounds really good. I use PBN Mini-Olympias which can be run in stereo or as bridged monoblocks in either high ( AB ) bias or low ( A ) bias. While they certainly don't push the same kind of output wattage in low-bias mode as in high-bias mode, they still provide plenty enough grunt to drive my 83 dB-efficient ( ??? ) PMC fact.12's to as loud as I'd ever want to hear them in this room.... sounds lovely but you bet they throw some heat off.

D.D.

 

I see that Sugden is imported by ToneAudio. Pass. I don't like to pay over-inflated prices and get terrible service.

 

I'm curious, why is it you're seeking a class A amplifier? I get that you like the sound of an M22, but is your A-S2100 not up to snuff, or are you putting together another system?

This cheesy review claims the A-S2100 sounds just as good as an old A/AB CA-2010.