Should I buy a Class A Amp.


I would Love to buy a Class A Amp. I have a Sony Tan-80ES Amp right now and I have had it for 19 yrs. To me it sounds Great but I am curious about Class A Amps. Do they really sound better? I am looking at a Krell KSA 200 Amp right now for $2000.00. It is older then my Sony. Is this too much for such an old Amp? Would Love to hear members thoughts on this.  

Blessings, ..........Don.
donplatt
I don't think Class A is what it used to be. :) That is, amplifiers are a lot better. I traded an amp that was Class A up to 35 Watts for an ICEPower unit and never regretted it.  It's better for my power bill and the planet. :)

Personally, I find Krell to be powerful, but not particularly interesting, and the age of the KSA 200 makes it way overpriced to me.

Save your money.  If you want an amplifier that adds to your experience, as opposed to just transmits the music, maybe a tube amp would be worth listening to.  If you must have Class-A, then the Pass amps are probably going to be the best exemplars. For afford-ability, how about a Parasound A21, class A until 20 watts or so.  Very neutral.

If you want to be a bit of a geek ( and who doesn't? ) The Ncore monoblock kits are running around $1,200 US for a stereo pair. IMHO a much better investment than an old Krell, unless you happen to have the Apogee Scintilla's to go with them. :)

Godesses, I hope this starts a flame war worth having. :)

Best,


Erik
Thanks Eric for your Response. Very Helpful! 

......Don.
I would either go with the latest Class D or pick up the pair of Mcintosh MC 60s on eBay right now. I have both and although they are a little different in their own way, both are probably more dependable and sound better than a dated Krell/transistor amp. 

Which Class D Amp did you buy Eric?   


Blessings.........Don.
donplatt

Hi, although I like Krells very much there were only two that were real Class A the other were either "high" biased into Class A or sliding (plataue) bias types.
These two Krell that were real Class A were the ones that were fan forced cooled (no heatsinks on the outside) and were the KSA-50 and KSA-100 which may have come as monoblock form as well.

http://www.stereophile.com/solidpoweramps/985krell/#wCIDLgktMRqomRuM.97

http://img.canuckaudiomart.com/uploads/large/853586-krell-ksa-100-mk2-completely-rebuilt.jpg

Cheers George 
Hi Don!

Like my speakers, I rolled my own. :)  I came across a great deal on used, stock ICEPower 250ASP modules, and put them together with Chinese sourced cases and silver signal wire.

Originally I was going to use the ICEPower units to power my HT speakers, so Center and Surround, but I ended up with six amp modules instead of three. I had a Parasound A23 amplifier at the time, about the same rated power, but idle was 140 Watts, vs. 30 for the ICEPower pair. I honestly could hear no difference at all between the two amplifiers, so I kept the cheap small cold one's and use them exclusively.

With a little more funding I might have played with warming up the sound a bit, but having just moved, I just don't have the time or space.

Best,


Erik
Ahhh, right, Krell's sliding bias thing. Still, my point, and really my only point, is don't be mesmerized by a technology. Just because an amp says "Class F" or "Zero Feedback" is rarely a reason you should personally buy one or the other.

Use your ears,and don't spend money unless the differences you hear are worth the spend.


Best,


Erik
Thanks Again!   

.......Don.
What is your real question Don?
Do you want to know whether a random Class A amplifier will sound better than your current  Sony Tan-80ES Amp  (which sounds "great" to you)?
Or, do you want to know whether $2,000 is an appropriate price for a used  Krell KSA 200 Amp? 
Can you give us some background on why you would " Love to buy a Class A Amp"?
What is your price range and what do you wish to accomplish with your system by purchasing a Class A amplifier?
How much power do you need and what speakers are you trying to drive?
BTW, your amp is a Sony TA-N80ES and is rated at 200wpc but it nowhere near doubles power into 4 ohms, which implies it may struggle with speakers having low impedance inputs or impedance variations throughout the frequency range.
It sort of sounds to me as if you have heard that Class A amplifiers are inherently "better" than other amplifier topologies and you saw this Krell for an amount of money you can afford so you would like to go ahead and purchase it and you want a bunch of folks to support your purchase decision.
My answer is not meant to be condescending but to point out the risks of asking for "help" in spending your money from a forum where everyone has their own biases.  Fortunately, you have received some solid advice from Erik and George here.  I certainly agree with Erik's  comments,
don't be mesmerized by a technology. Just because an amp says "Class F" or "Zero Feedback" is rarely a reason you should personally buy one or the other.
Although, I would add "Class D" to his list of technologies.
I also agree that you would gain perspective by following another of Erik's recommendations,
maybe a tube amp would be worth listening to
And, I particularly agree with his statement,
Use your ears,and don't spend money unless the differences you hear are worth the spend.
 However, i don't agree with his statement,
I don't think Class A is what it used to be.
I have two excellent sounding Class A amplifiers here now, a pair of Lamm M1.2 Reference amps and a pair of Clayton M300 Class A amps.  I also have another excellent sounding Class AB amplifier, a McCormack DNA-2 LAE that has been fully upgraded by SMc Audio.  All three sound better to me than Ncore's latest Class D effort, the NC1200 modules in the Acoustic Imagery Atsah amplifiers.
So, I would say that Class A is an inherently superior topology for certain technical reasons but, like anything, different implementations will sound different.  Also, because they are biased to output full power all the time, the build quality of Class A amplifiers must be VERY robust for reliability so it may not be a good move to purchase older or less expensive versions of the topology.  That said, I have heard pretty good reports about the Monarchy Class A amplifiers at reasonable price points.
Regarding Class D, I would say that, at lower prices they can offer very good value.  As you pay for better implementations, they can sound quite good but at the upper price ranges the topology is not capable of competing with well-implemented Class A or AB amplifiers IMO. 
Go listen to some amplifiers, preferably with your own speakers or, if your Sony amp sounds "great" to you, go buy some music and be happy with the sound of your system.
Good luck.
Use your own ears to decide. Lots of very well meaning members here who know a LOT about audio and they base their opinions on their ears but in the end it is about YOUR ears. I like to use the analogy of wine tasting and taste buds. A great wine for you is one that taste great to you.

If a friend of mine asked me if he should buy a class A amp I would say don't do it unless you know you have to because you have speakers that really need class A. And I assume you already know that amp / speaker pairing is so critical. The best amp with the wrong speaker will still sound like crap.

Do you have a local audio club in your area. It is a great way to get exposure and listening opportunities to high end amps.


This is just my opinion, but I think I have heard probably more amps than most people on here, having been in the high end business for 25 years.  Not much I haven't heard.

The absolute best amps that I have owned and heard have been Class A amps.  Something special about that design.  They do suck power and run extremely hot, (the hotter they are, the better they sound).

However, I do agree with the comments above about hearing them in your own system, in your own room, with your own music.

May not be your cup o' tea?
Once you've lived with a "good" pure Class A solid state amp it's hard to go back even to a highly biased Class A a/b amp.
The sound just seems to envelop you from speakers with an ease, without being drawn to them, that the sound is coming from elsewhere in the sound stage rather than emanating from them.

Cheers George  
Don't be fooled by different amp designs.  Some Class A amps sound terrible, some Class AB sound wonderful.  Those are not the only designs out there.  And there are a lot of variations to those designs.  You need to listen to specific amps in your system to determine what you like. 

What is very important is the matching of the amp to the upstream and downstream components.  The amp MUST have a sufficiently high input impedance to allow the preamp to drive it.  Give yourself a chance to upgrade to a high output impedance tube preamp if you want. 

The amp must be stable into the bizarre loads presented to it by the speakers.  Give yourself a chance to change speakers without creating an issue with speaker matching.

Good amps will have high input impedance and run stable into a very wide range of resistive, inductive and capacitative loads. 

Not trying to start a flame war, but I personally don't think the Krell is a particularly good amp, certainly nothing to write home about.  IMO, certain speakers might sound OK, but the speakers have to cover the Krell's shortcomings.  Just my opinion.  YMMV. 



Hi Mitch!

I don’t think we’re saying anything differently, but there was a minor miscommunication.

I don’t mean that Class-A has gotten worse, but rather, the gap between Class A and other amplifier technology has gotten smaller thanks to non-pure Class A amplifiers getting better.  As a result some of the sheen has rubbed off the "Class-A" brand.

Sorry for the misunderstanding.

Best,


Erik

I agree with earlier posters that there are a number of factors affecting the sound of amps, including the speaker load, how loud you listen, and a vast number of factors in the amp design itself.  And you have to remember that most Class AB amps run full Class A until they reach a certain output level when they begin switching into Class AB, and then further up the output curve they switch into Class B.  If you have sensitive speakers and/or easy loads, your current amp (no pun intended) may already be running in Class A.

The old Class A dreadnaughts of which the Krell KSA series is one, along with Mark Levinson, Threshold, NRG Control, and others were primarily designed to run Class A into low sensitivity speakers with difficult loads like some Thiels and planar and ribbon speakers like Apogees and SoundLabs.  Nelson Pass of Threshold and now Pass Labs says you can really tell whether an amp is running true Class A by its weight as the required massive transformers and heatsinks weigh a lot.  As previously stated, Class A amps have all of their output devices running full-out all the time and divert all output into heat and the speaker load.  As the volume output increases they divert more of the current into the speaker load and less into heat.  However, these monster amps may not have necessarily sounded the best, especially when they were only outputting small amounts into the speaker load and mostly into heat.

IMO, the use of Class A does not always guarantee the best sound, especially since "sound" is largely subjective.  Perhaps if you have a difficult load this might be true more times than not, but if it were me I would listen to some different designs with good reputations like those mentioned previously.  I use some esoteric equipment by Essence that came in Class A and Class AB designs and I liked the Class AB presentation better.  The Class A monoblocks used a more massive power supply and the sound was more robust and had more bass weight.  The Class AB stereo amp was much faster, transparent, and had a more prominent and extended treble, which was a better match with my speakers.

Good luck.

I have heard great AB amps and great A amps.  From my understanding a class A is an inherently better circuit but the implementation is what also makes a difference.

i currently run a Boulder 2060 amp.  If you look it up, it's a class A beast and I have not had anything as good.  I had a class AB Classe m600 and also heard a class AB rotel 1590... Nowhere close.
I Thank all of you for your Responses. I should tell you that I have Eminent 8B Speakers. 83db @ 8 Ohmns. 

.........Don.
Mitch2  +1   Also, take into account the operating costs and add-ons. With listening every evening, the Class A design costs me an additional $20/month - not including the AC in the summer to compensate for the heat. Chances are good that different cabling will be needed to tweak system synergy with a different amp. Later, there are always visits to the repair tech. But, yes I do enjoy my Class A very much.
I've had my Levinson 20.6's for almost 25 years and would never even consider selling. Have heard a lot of other amplifiers but none of them would make me retire the 20.6's. So I would be the last to tell you to steer away from Class A amps. 

However, older amplifiers can cost a lot of money to service. Caps, diodes, trim pots and transistors can go bad after 20 plus years and it's not uncommon to get estimates in the $1000 to $2500 range to diagnose and repair vintage Krell, Levinson, Threshold, etc. 

Is Class A the best design? Look at it this way: no preamplifier designer would ever build anything other than Class A. The only reason that power amplifiers aren't all Class A is because the dollar to watt ratio is too high and the maximum power is usually limited to around 100 wpc. 
Listen for yourself.

My personal opinion - if you like silky mellifluous middles, do it. And get some Harbeths while you’re at it. :-)

If you like an analytical, sharper delivery - don’t. And IMHO the new Hypex modules beat everything else when it comes to resolving details - finetune it to your preference with speakers. Done.
Is Class A the best design? Look at it this way: no preamplifier designer would ever build anything other than Class A.
This statement says it all, if a preamp was a/b it wouldn’t sound very good, all decent preamps are class A.

It’s the same for Class A amps even more so, but you have to cop the negatives, heat, powersupply ability, size, weight, and power consumption.
All these negatives have nothing to do with poor sound quality, if fact it’s the opposite, Class A done "right" is superior to any a/b, b, d, h etc etc

Cheers George

I have an A/B amp that is biased pretty high into Class A, and my speakers are a real easy load. With this setup, I’m in Class A much of the time, and when I’m not, I honestly can’t hear it.

 From my perspective, it all depends on the amp implementation, listener preferences, and choice of speakers. I’ve had pure Class A amps cycle through the system, and I haven’t heard anything that would convince me to give up a *well-designed* A/B amplifier. BUT that’s on MY system. If the speakers were a lot harder to drive, and I listened a lot louder, then I probably would have gone with a Class A behemoth like a big Pass or Boulder.

 To answer Don’s original question: Though I think he need an amp with some serious cajones to drive his Eminents, I would probably stay away from that Krell. Only problem is, most pure Class A designs are gonna cost a good deal more than 2k, even used.

 


Don-


audition Pass Labs power amps. Happy Listening!

 FWIW, 
My Mark Levinson no. 334, the "Voltage Gain Stages" are biased to operate in a full class A mode in order to keep all devices within their most linear, distortion free ranges at all time. Using the proprietary adaptive biasing scheme developed in the no. 33 Reference mono's that deliver the sonic advantages of a Class A output stage without incuring the substantial inefficiencies and consequential thermal problems of pure Class A operation. Power output, 125w, 250w, 500w into 8-4-2ohms.

As a result I chose the less powerfull no.334 over the 335 or,336. I do not use any power conditioning or regeration equipment. Laws of physics cannot be denied. The Levinson no. 336 draws 50 amperes at 120v. Long term, you cannot deliver more power to a speaker than you can pull from your wall.

N
Well if you have techie near-by that you trust, If you live in colder zones and need extra heat, you should go for powerful class A amp.

Nice! Nutty-


what other gear, including cables/cords, is in your system?

nutty " ... My Mark Levinson no. 334, the "Voltage Gain Stages" are biased to operate in a full class A mode ... Laws of physics cannot be denied. The Levinson no. 336 draws 50 amperes at 120v ... "
That seems very dubious. It surely can’t draw 50A from a 20A line. How do you have this amplifier connected to AC?
I have a Rega R CD Player a Rega R Dac a Thorens 160B Turntable with a SME 3009 series 2 improved tonearm with a Grado Platinum Cart.  I also have Tara Labs Interconnects and finally Luminous Silver Speaker Cable. No Power Cords except the ones that came with the Components.
jafant,

Ayre cx7emp, CD OEM power cord
Classe CP60 , Nordost Brahma power cord
Mark Levinson no 334, Voodoo cable Fire power cord, 8awg
Totem hawk speakers

Straigtwire Crescendo balanced interconnects
(Sometimes I run Audioquest Cheetah silver interconnects w/dbs)
Audioquest Gibralter speaker wire, 2 full shotgun runs for true biwire.
(I’m waiting for Paul at Clear Day to send me some cables for demo)

N

Hi Don,

In terms of their impedance characteristics, your Eminent Technology LFT-8B speakers are exceptionally easy to drive compared to most others. And their wavelaunch characteristics, which are essentially planar above the deep bass region, mean that at typical listening distances their 83 db sensitivity rating is equivalent to the sensitivities of box-type speakers that are rated at least several db higher.

Therefore the ability of an amplifier such as the KSA-200 to supply huge amounts of current and power into very low impedances would be unlikely to provide any benefit with your speakers. Meaning that a considerable fraction of your amplifier dollars would be going toward amplifier capabilities that you don’t need.

Also, as has been alluded to the age of such an amp suggests that condition-related issues stand a good chance of surfacing sooner rather than later, and repairs can be expected to be expensive.

That said, I would expect that an amplifier upgrade of some sort is likely to provide significant benefit. I say that in part because the extremely "good" specs on your Sony TA-N80ES amp for THD and IMD are suggestive of the likelihood that feedback has been applied in the design in a heavy-handed manner, which can often do more sonic harm than good.

Also, if by any chance you are using the balanced inputs of the Sony amp, I would definitely try changing to the unbalanced inputs. I say that in part because its balanced inputs have an input impedance of only 600 ohms, which most consumer equipment cannot drive with optimal or even good results, and in part because the writeup I linked to indicates that the balanced inputs were implemented using "rather low-end componentry."

The bottom line on what I would do regarding an amplifier upgrade is to begin by researching what amplifiers others have reported to provide good results with your particular speakers. And then consider whichever of those strike your fancy and suit your budget, regardless of whether it is class A, AB, or D, and whether it is tube or solid state. While keeping in mind that the manual for your speakers recommends amplifier power ratings of between 75 and 200 watts.

Best of luck. Regards,
-- Al

cleeds,

The 300 series amplifiers operate as virtual perfect textbook cases as a "Voltage Source". This is to say that "They" will maintain whatever the appropriate voltage might be at any moment (given the demands of music, and within the rated output voltage of the amplifier) without any particular regard for the current demands of the loudspeaker.

Because of this "Voltage Source" characteristic, the 300 series amplifiers double their output everytime the loudspeaker impedance is cut by half. For example the no.336’s continuous output is 350 watts per channel @8ohms, 700 watts per channel @4ohms and 1400 watts @2 ohms- assuming the electrical circuit in the wall can support these extraordinary power levels. A "continuous" 2ohm test of the no.336 at maximum power would require 50 amperes at 120v.

No known high quality loudspeaker can absorb the continuous full power of the no. 336. However, many high quality loudspeakers can handle rather extreme power levels on a "Short Term" basis when reproducing music at realistic levels. The 300 series amplifiers answer these needs with impunity, without any power supply sag and without altering their sonic performance in any way.

Unfortunately, the thermal management problems in true Class A in a "High Current Output Stage" can be severe and offer sonic compromises of their own. For this reason, the Levinson 300 series are not Class A biased in a traditional fashion.
(All "Voltage Gain Stages" are biased to operate in full Class A mode in order to keep the active device safely within their most linear range at all times).

N
What a great thread has been created.  I need to make more friends like this. :)

The other thing, one not often mentioned, is that if your ears can't tell a difference, don't spend the money. Stereo equipment, like cars, rarely ages well. It's not worth spending $20 for a "better" amplifier if you can't hear the difference. OF course, reliability, size, power all matter too.  I just meant that no matter what the consensus may be of a particular piece of gear, spend your money for you, not others. :) That $20 could better be spent on a new LP.

Best,

Erik
I'm with czarivey...if you live in the Sakha region of Russia and you're at 20 degrees below freezing and hope to accomplish the dual task of listening to music while preventing hypothermia, buy yourself a nice Class A amp.   They make wonderful space heaters in the winter.    Otherwise, no thanks.  I personally went Class D and never looked back.    440wpc and you couldn't melt a slice of cheese on it.  Great sound + energy efficiency = happy times.
Class A amplifier's!, don't Look back!

Why would class A operation make an amp slower? Is it inherent in the design? I don't understand these things.
Another question is is the full class A amp a simpler design that just has to be executed well to make sense?
FWIW...Class A: This amp technology can best be described by saying it analyzes and amplifies the full 360 degree cycles (positive to negative) of the incoming audio waveforms in absolute real time. To be able to do that, it’s pretty much running at full power all the time. Whether the music you’re listening to is soft, loud or anywhere in between, the amp is using all of its available energy 100% of the time to reproduce it.

N
inna2,067 posts07-19-2016 7:39amWhy would class A operation make an amp slower? Is it inherent in the design? I don’t understand these things.
Another question is is the full class A amp a simpler design that just has to be executed well to make sense?

Class A done right will not be slower, some say this, but it’s just poor design eg: power supply not being up to constant draw on it etc.

And no, a proper designed Class A is more complex, re heat power supply etc.

OK a bit of why I love Class A so much.
I built a pure class A 150w back in the 70’s a three man lift (best amp I or anyone ever heard nothing came close to it) so easy to listen to, huge dynamics, massive sound stage, pinpoint image with depth. But the dynamics were not in a forced way that shot out from the individual drivers, but in whole envelopling way, that washed over you, with it’s bigness and dynamics

But this amp had a 2 x 5kva transformers with 220,000uf capcitance per channel, 18 per channel for memory Hirel EB203 ED204 tranistors, and the big one the whole heatsink was water cooled with it’s own small radiator, variable speed radiator fan and silent water pump to keep the output transistors heat stable,

This amp drove a mates double stacked quad ESL57’s with Decca Kelly ribbons from 10khz up, two x 24" Hartley woofers mounted in the back brick wall, using the next room as the speaker box. The sound was sublime.

The sources were Linn LP12 Black Widow arm and a Stax electrostatic cartridge, that need to be tuned in with it’s own tube supply and scope that took 1/2hr but only stayed in tune for around 1hr before needing to be re-tuned again because humidity changes. We fed that into the amp via my first MkI Lightspeed passive pre.

If you can find them the Mark Levinson ML2 monoblocks are massive but only put out 25w pure class A
They will drive any nasty speaker load, but the speaker has to be reasonably high in efficiency, eg > say 88dB
 


Cheers George
alzo spracht nutty:

" For example the no.336’s continuous output is 350 watts per channel @8ohms, 700 watts per channel @4ohms and 1400 watts @2 ohms- assuming the electrical circuit in the wall can support these extraordinary power levels. A "continuous" 2ohm test of the no.336 at maximum power would require 50 amperes at 120v. "

If you're a drivin' that there amp from a 20A line source, you ain't a gunuh make that there amp draw no 50 amps.  Caint do et.  Caint take what aint there.  Dont matur what kinda cabuls you're a usin.  If you're a using a standurd 15-5R wall plug, you aint a pullun no 50 amps

Just what kinduh fulz duz you thenk we ar?

Sum uf us are enjuneres.   

I have a pass 30.5 class A......just put up my new Martin Logan
60 XT speakers.....need more burn in time 4 speakers......but
everything is starting to open up..... but I guess what I am trying
to say is if you sat n listened to a pass class A amp you would
love it..... PassLabs makes great sounding equipment built 2
last..... n everyone I know or who  reviewed pass amps has
said there class A amps our there best amps.......................

and they make some of the best amps out there.....n remember
pass is one of the few high end company's still owned by its
maker....like Mc intosh--- Marantz--- Mark Levinson etc...used
2 be.......check out Reno HiFI....mark will let you demo one......

Good Luck.....henry.
George, thank you.
Would you some people mind writing in normal English?
bpoletti,

No need for sarcasm...We’re all friends here. If you do not understand the post please read it in its entirety again.

I apologize if I’ve confused you. It reads:
"assuming" (again assuming), the electrical circuit in the wall can support these extraordinary power levels, a "continuous" 2ohm test of the no.336 at maximum power would require 50 amperes at 120v."

That is why Levinson chose to design the the 300 series amplifiers "VOLTAGE GAIN STAGES" into Class A and not in the traditional "HIGH CURRENT OUTPUT" fashion.

Additionally, my data is largly derived directly from Mark Levinson documentation.

Best regards
N




inna2,069 posts07-19-2016 11:09amGeorge, thank you.
Would you some people mind writing in normal English?

Sorry inna, that was more for the techs here, who want to know why I’m in favour of well designed Class A amps

BTW: I noticed my link to the Mark Levinson ML2  25w Class A mono block beasts didn’t take here it is.
http://www.highendclassics.com/brands/marklevinsonml2-2

Cheers George
nutty

Not sure where you're getting the 1400watt output number.  ML's specs indicate 2 ohm output to 500wpc. 

Please post the source for the specs you claim. 


bpoletti,

I'm getting my specs from my manual. My system with the no. 334 is 125w 8ohm, 250w 4ohm, 500w 2ohm.
The no. 336 referenced in the post is rated 1400w 2ohm. 

N


The 300 series ML’s are high biased class A/B, B after the bias runs out, they are not pure Class A.
Looking at the heatsinks I say about 20-30w Class A bias max, as Stereophile also said they weren’t too hot to touch, even after 1 hour pre-conditioning at 1/3rd power.
If they were pure Class A they’d be the size of a very large coffee table with heatsinks big enough to warm the whole neighborhood.

Stereophile full power tests on the No.334 are at 1% THD!!!.
8ohm = 139.9w
4ohm = 243w
2ohm = 430w

Bottom of the page measurement chart
http://www.stereophile.com/content/mark-levinson-no334-power-amplifier-measurements-page-3#toJJo0Xxp6m0aqe4.97

Cheers George
What about older Rowlands, 8T and 9T, and even older 5 and 7, how were they doing in terms of class A? Gryphons, I think, were and perhaps still are pure class A.
All high bias Class A/B I think except for an early massive Gryphon which was suppose to be pure class A to clipping into 8ohms.

You just have to look at the old huge ML25 monoblocks which were 25w pure class A only into 8ohms. The heat factor goes up exponentially the more watts there are, because the rail volts have be to increased.

So for two amps, one 20w class A that’s all.
And the other 100watts class A/B still with only 20w of Class A bias, this amp will be 4 x hotter. Even though their both only 20w Class A.
This is why I had to water cool the amp I made 4 posts back because I wanted 150w and Class A all the way.
Cheers George
I see.
What happened to your built amp or you still use it?
After 20 years of use even though all metal parts were aluminium, electrolysis started, it started to get corrosion, it was getting dangerous, so I rebuilt it into a normal big amp with big heat sinks hi bias first 30w Class A  and sold it.

Cheers George
george,

Thanks for taking time to research the specifications of the amplifier and for your professional decorum. I actually have an original copy of the Stereophile Magazine with the article. Due to the age of my unit, I had it serviced just over a year ago and returned to factory specifications.

I agree with your statement above. A/B application. 
An important aspect of the design was the implementation of a new sliding-bias output-stage topology which Madrigal calls "Adaptive Biasing." The design goal was for the 300 series to function as a true voltage source for any loudspeaker load between 8 ohms and 2 ohms. (The No.33 Reference extends this ability down to 1 ohm.)
"As discussed in one of the company’s white papers, an amplifier rated for this range of impedance loads needs a high level of output bias to minimize crossover distortion and to avoid any possibility of reverse-biasing an output device. In a traditional class-A design, this leads to a large quiescent current draw, hence the production of a lot of heat. Madrigal’s solution was to modulate the bias level as a function of the input signal, using an algorithm that includes both the input signal and the level of output current being demanded by the loudspeaker."

All the best,
N

To bpoleti in copy, I would like to reiterate that I never stated that I was operating the no.336. Nor that I was drawing 50 amperes from a 120hz outlet.

Madrigal states in my manual "...Because of this "Voltage Source" characteristic, the 300 series amplifiers double their output everytime the loudspeaker impedance is cut by half. For example the no.336’s continuous output is 350 watts per channel @8ohms, 700 watts per channel @4ohms and 1400 watts @2 ohms- assuming the electrical circuit in the wall can support these extraordinary power levels. A "continuous" 2ohm test of the no.336 at maximum power would require 50 amperes at 120v..."