??? WHY WHY WHY ??? Class A vs Everything Else


 After 8 long months at the Authorized U.S.Service Center,my beautiful Sugden Bijou Class A amplifier & PreAmp came home 2 days ago..BOTH units have been completely,& I mean COMPLETELY rebuilt,from input stages to output stages,pretty much  everything was replaced with new components,checked,cleaned,rebiased & cooked in...
 For the last 8 months I've alternated between a Class A/B SimAudio Moon 240i & a Class D,Creek 4040A..I really like the Class D Creek and it will accompany me on an upcoming 3 year job in the Philippines starting this coming November..I was all set to put the Sugden gear up for sale as soon as it came in & I confirmed operation..I NEVER should have set it up!!!
 Using the Moon 240i as a preamp since I don't have a stand alone source to feed the Sugden HeadMaster,I set up the MusicMaster amp & let it warm up for 15 minutes...
 From the VERY FIRST NOTES,I was enchanted.mesmerized,enthralled,seduced & completely gobsmacked...
 There was something soooo right about the sound..There isn't one area I could point to,it simply sounds.right..Everything seems to have been lit from inside..The best analogy I can provide is this..The sound is like the colors of nature,as the rising sun just clears the horizon & suddenly everything snaps into vivid focus,taking your breath away...
 I spent the better part of today swapping in & out between all 3 amplifiers on hand just to make sure I wasn't simply locked into subconscious justification for spending the $ to have the Sugden gear rebuilt..I wasn't!
 I hate having gear sitting in a box unused but I'm not sure I have any choice in this situation..When I come home on breaks during this upcoming project & when it is finally finished & I come back to the States for good I'll have it to enjoy..Not to mention it will cost a small fortune by then to replace the level of performance of this gear offers with whatever happens to be the flavor of that time...
 WTH can't everything just sound this superb.......
 

freediver

I built a Hiraga Super 30 Class A amp. It is the amp I listen to most, just does everything well. Lots of detail, without being fatiguing. Amazing 3d soundstage, with clear imaging. Rich mids and tight bass. Is very responsive to upstream components, showcases differences in the front end. Works well with most of my speakers, though it’s too much with my Cornwalls in the low end - my Type 45 plays better with those. 
 

One thing I noticed, is how well it plays at low listening levels. 
 

I would love to get my hands on a GanFet Class D amp, so I could compare the two. I have class A tube and solid state (single ended and push pull of both). Several different types of amps based on different output tubes. 
 

They all have their “thing”they do well. And depending on what I’m listening to, speakers and amps will be swapped in and out.

 

But is the Hiraga I keep coming back to. 

Something about Class A, something about Sugden.  I've owned/own 5 pieces.  Only one that disappointed was an A21SE CD player.  Not!!!  Have fun.

The choice between Class A operation vs Class AB comes down to a simple decision between:

(A) Inherent low distortion and absence of device switching over the entire waveform, and also the least efficient mode of operation.

(AB) Significantly higher efficiency, greater power output (typically 3X or more) and an implied requirement for local or global feedback to linearize the switching transition in the output devices.

So if you’re building a transistor or tube power amp, the only difference from a design perspective is the rail or B+ voltage and the operating point for the output devices. Class A operation involves lower voltages but a high standing current ... in effect, the amplifier draws the same amount of power from the AC line, whether it is idling or at clipping. So it runs hot all the time. They are room heaters, thanks to low efficiency.

Class AB has the interesting property that AC power draw varies with signal level; this has implications for power supply design, since current flow through the supply is program modulated, and not in a simple way. This is a roundabout way of saying Class AB amplifiers need better power supplies, and full regulation isn’t a bad idea. Otherwise, 100/120 Hz rectification buzz in the audio signal will be program modulated, which is extremely undesirable.

There is an additional complication which applies to solid-state but not tube amplifiers. Tubes don’t need heat sinks, since device characteristics are not affected by operating temperature, and they are designed to radiate heat on their own without assistance.

Transistors can be destroyed by high device temperature, or have their useful lives shortened. The failure mode is complete destruction, which happens without warning, and might expose the loudspeaker to full rail voltage, which will destroy it.

In practice, transistor amps operating in Class A need substantial heat-sinking and effective temperature monitoring to prevent runaway thermal faults. These additional circuits must be highly reliable, since runaway thermal faults will destroy the output section before the user can get to the power switch.

In tube amps, Class A versus Class AB is a simple decision between power output versus linearity. Not much to it. In transistor amps, in addition to a significant power derating, Class A implies good thermal management if the amp is to be reliable.

In practice, transistor amps that operate in true Class A are thermally limited. How big a heat sink will the consumer accept, and are fans acceptable?

(Note: there are various sliding-bias schemes, which have been around since the Seventies, that claim to be Class A. They’re not. Non-switching is not the same as Class A.)

For some reason, Doug Dale has figured out how to design my (his) Coda s5.5 amp which produces 50 wpc class A into 8 ohm and 100 amp current so that it is not very warm to the touch and really makes very little heat. You can comfortably place your hand on the amp and leave it there. The heat sync seem to not be very warm either. It's a rather powerful little amp for what it is. Oh, and it sounds wonderful to me.

As an owner of an Esoteric A-03 Class A has many virtues but also some shortcomings. Dynamics/Headroom are minimized due to lower power and the relaxed sound of Class A. Transient Speed and Bass Slam can also be effected. Many Class A amps have an oversaturation(IMO) of color Accuphase/Pass Labs to name of few. Be careful of buying a Pure Class A integrated due to excessive heat entering the Preamp section. Even with these issues Class A amplification can provide the most coherent and balanced sound available. IMO the best Class A strength is the Non-Mechanical flow of music that only the best Class AB power amps can approach.