Ciro71, you mentioned Vitus Audio SS101. I'm interested. Can you elaborate more on its sonic characteristics compared to the Burmester 911 Mk3? |
I have been reading some outstanding reviews of the new Hegel H30. When 1000 wpc is just not good enough! :) |
Atmasphere,
I agree with what you wrote.
Push-pull can be class A or AB, flexability.
Single end is limited to class A operation only, no fleability in this regard. |
Thank god, now I can listen to my M60s and not worry about it:) |
Class A has two modes of execution, A1 and A2. In A1 the output devices conduct all the time and there is no current flowing in the grid circuit (we are talking tubes here). In class A2 the output devices also conduct all the time but there is grid current flowing during part of the cycle. For the latter there are design considerations required to prevent distortion due to driver circuit issues.
Rleff, our amps are A2. 'Pure class A' has no engineering or technical significance (although it may have marketing significance); IOW an amplifier is 'pure class A' whether it is class A1 or A2.
It does not matter if an amplifier is single-ended or push-pull, it can be class A1 or A2 in any of those embodiments. |
George ,
You certainly could be right about the class A vs A1 distinction. The designer does mention he`s able to get 21 watts per KT-88 tube as opposed to 18 watts per tube.Is there really much difference between the two types of class A ? I`d love to hear this very unique amplifier. |
I'd like to see the circuit when and if he publishes it.
Just noticed it also says it is run in Class A1, not Class A. Some tube gurus say the extra couple of watts gained from Class A1 is a backward step, rather a couple less watts and pure class A. I don't know never compared the two. It's getting good press and got all us talking about it.
I built a copy of the SET DHT Wavac MD805m mono blocks once no expense spared for transformers, complete with 300b driver and interstage transformers to the 805 RCA tube, the better I tweaked the circuit for sound, the closer I got to to one of my Class A water cooled solid state amps, in the end I stuck with class A solid state.
Cheers George |
Actually to be correct the design is 'six amps per side' for a total of 12 single end amplifiers.
Regards, |
Hi George,
Reading the amplifier designer`s description says it`s made of 6 seperate 'single ended'(not push-pull) KT-88 all connected together and divided into two monoblocks. |
This is correct the bias on a true SET amp increases and decreases the power (watts) and it stays class A. And then there's Class A1 with SET's that's another kettle of fish.
But what you said about Vick's amp was
"vicks,Your amplifier is 'single ended' with the KT88?"
And I said "no I think it's a hybrid of some sorts that acts like single ended."
Cheers George |
What I saying is if a tube is run as SET/SET-P(parallel) be they DHT or pentode(KT-88 in this case) it can 'only' be done in full class A operation i.e. there`s no class B portion possible with SET design. |
I don't think they are single ended as they have series and parallel output tubes, this is said to behave like single ended without actually being single ended.
http://www.6moons.com/industryfeatures/audiopax2/4.html
Cheers George |
vicks,
Your amplifier is 'single ended' with the KT88? Are`nt SET amps pure class A by virtue of design(they can`t be class AB I believe). |
Thanks George. I have had the pleasure of meeting the Audiopax designer, Eduardo, on a few occasions. A true genius and I believe he has produced something very special with this new amplifier. Early days still - I just hope people get the chance to audition these. |
Yes James I believe these are class A most of the way, I know a friend of the designer here in Australia, Elson Silva, he builds "Cymer" amps here, he says there is just the same amount of fudging of class A amounts in the tube circles as well as solid state.
Cheers George |
The Audiopax Maggiore is a true 100W Class A amplifier so the "stretching the bow" comment does not apply in this case. |
Reference Line Silver Signature from the late '90s. 100 watts into 8 ohms, doubles all the way down to 2 ohm loads. Designed for passive preamps and runs hot, so you have to be okay with those features. Top quality internal components. Built to last forever. Amazing transparency and ease. |
Ralph, are the M60s pure class A? Not that I care, except theortically. I do remember when I bought my CAT JL2 that Ken Stevens scoffed at claims others made about being Class A (he had an SS design in mind), but I think his amp was pur Class A, it sure was hot enough, raising the room temp 5-7 degrees. |
Rleff, The idea was an analog setup that used a feedforward system so that the bias is mapped in sync with the output signal. In effect there would be no 'decision point', merely a minimum level that represents no signal at all- as soon as you have some signal, the bias is increased or decreased in exact synchronization with the signal, so the amplifier is always operating in the class A region. However so far things have gone if favor of the KISS principle- So far the evidence suggests that such a system will produce some artifact. |
I believe the "power envelope" did nothing extra for the class A bias.
What I believe it did do was to aid in transient ability with a bit more short term current from the power supply. This way they saved on big expensive power supplies, and got a result that was better than using a mediocre supply.
I lifted this explanation from DIY audio, make of it what you will.
"The cheaper PE receivers used two ± power supply rails with a fast diode on the lower rails feeding the outputs, a polyswitch was in series with the upper rails."
Cheers George |
Question: NAD "Power Envelope" amps....Hope I'm not
going too far off topic, but with the recent comments
about sliding bias circuitry, I'm genuinely curious
about what, if any, similarities exist between the
NAD 2600a method (mid 1990's) and the Krell method.
The NAD's have never been called Class A, have they ? |
Thx Rx8man, my real name should have been georgehifi but for some reason Audiogon would not let me use this, so I went with the next thing I could remember.
Here is a more descriptive post of the self contained water cooled class A I built.
http://www.stereo.net.au/forums/showthread.php/37548-Living-with-Pure-Class-A-in-Australia?p=560887&viewfull=1#post560887
Cheers George |
Ralph how would you decide on what power the class would change at if you were to attempt using the MA1 as a example? I am just curious.
|
03-06-12: Doggiehowser: Didn't Nelson Pass create the sliding bias thingamabob? :03-06-12: Doggiehowser
In actual fact my ex boss (Steven Deratz) invented the first sliding bias system back in 1978 and had a world wide provisional patent on it for a couple of years. But his system worked a bit like negative feedback, it monitored the signal and tried to adjust the bias up and down in real time which was a loosing battle because it was never in real time, just like global negative feedback.
I don't think Nelson ever had an auto bias system just an optical bias system which was on the S300/S500 MkII's, when he did Class A he went more for the real thing.
Later Krells plateau bias where it kick it up and stays for a while and gradually comes down is the next best. But think about it the initial (first) transient is not in class A because it lags behind like my ex boss's system (so it's class B "harsh") then if successive transients "lower" than the original follow all's good they are in class A, if higher they are in class B again, and if there is a quite passage the bias drops down again and it starts all over again.
This is why, I strongly believe that proper hard biased Class A cannot be by any auto adjustable type system.
Cheers George |
George, I'm mightily impressed by your abilities (to take on such a challenging project) Beautiful work.
Your real name should be Georgehifi+!! |
I remember being approached by someone in the early 90s that held a patent to a sliding class A bias system (for transistors). As innovative as he is, I don't think Nelson created that. As I recall, it showed up on the Krell amps first.
We didn't go for it because our amps are tube. But I have thought about a tube-implemented class A system over the years. It might cool our amps off a bit! |
Didn't Nelson Pass create the sliding bias thingamabob?
:)
So does this sliding bias affect what George was talking about earlier when he said there was no way amplifiers could do 100s of watts of power in Class A mode? |
@Doggiehowser
The construction of the Karans are obviously different to a "traditional" Class-A design, as explained below(source: http://www.6moons.com/audioreviews/asi4/3.html):
"All Karan power amplifiers are characterized by a continuous sliding bias control. This is unlike the sliding bias used by Krell. Krell raised and lowered bias in predetermined steps like Mayan pyramids. In Karan designs an electronic circuit measures the incoming signalÂ’s amplitude. If there's need for additional output power, the current on the power rails which supply the class A output transistors is raised instantaneously. When the input amplitude goes down again, the bias follows suit. This way the output transistors always obtain the right amount of current and the operational temperature of this hugely powerful class A amplifier remains luke warm even when driven very hard."
I can't tell how this might influence the character of the sound, but it seems like a very clever design with the benefits of less power consumption, (much)less heat and the possibility of a more compact(well...:) enclosure. |
Krells are great amps, just that we were mislead quite a bit by many manufactures even today about Class A.
eg: Zaphod1000 said he once measure Musical Fidelity's little A1 integrated (you know the one, you wanted to wipe your feet on it)in spec, at 2 odd watts class A, they quoted 20watts!!
And their big daddy of yester year the A370 at 12 watts, they quoted 185watts!!.
Cheers George
|
@Sidekick I do agree the Karans do sound good but their claims for 470W Class A in that chassis that's comparable in size to the Krell 25W mono blocks seems odd, don't you think? |
Love to see that brochure. In any event, they sure fooled me. Still thought they were great sounding amps. I couldn't get past the sound of those fans on their predecessors. |
The KSA80 and KMA160 did preceed the KSA250, but they were still Class A/B amps. I have a brochure somewhere around where Krell acknowledge the power consuption of the amps. The power consumption is a dead giveaway that they were not Class A designs. |
The Krell KSA80, KMA160, et al were not Class A designs. They were Class A/B amplifiers, which operated with elevated Class A bias (usually to around 10% of their maximum power output). To the best of my knowledge, ONLY the fan cooled Krells were real Class A amps. |
Unsound: Georgelofi, I did see your link. I believe that at the time Mark Levinson was building those amps, he was charting fairly new territory, and those amps were overbuilt. Compare the size, weight & number of chassis, to a newer Class A amp capable of similar Class A power output:Unsound
This was what they needed just for 25w class A only , as they were still hot, after an hour or two idling, my friend owned a pair and I correctly biased them to spec for him, any hotter and they would have been unreliable.
Nelson Pass's favourite saying on how much class A bias heat sinks can handle, after 2hr warm up, is palms of hands on heat sinks with >35c ambient temp day and you should to handle the heat for 4 sec, this is the absolute max class A bias for those heatsinks. (brick layers need not apply for this test) soft wimpy tech hands or females only.
Cheers George |
Georgelofi, I did see your link. I believe that at the time Mark Levinson was building those amps, he was charting fairly new territory, and those amps were overbuilt. Compare the size, weight & number of chassis, to a newer Class A amp capable of similar Class A power output:
http://www.stereophile.com/content/pass-labs-xa305-power-amplifier-specifications
I think your overall point is well taken though. Some, if not many amps that suggest pure Class A output, are questionable in that regard.. The Aragon monos, the BEL's and some of the Electrocompaniet amplifiers amongst others, do appear to be stretching credibility with their Class A claims. |
They still are not anywhere near pure Class A up to their rated outputs, as you think they are.
I built quite a few pure class A amps back in the 80's based around this Nelson Pass circuit
http://www.passdiy.com/pdf/classa_amp.pdf
but expaned out to 100 watts instead of 20 watts. And I can tell you for 100 watts of pure class A, the first one was bigger than your large sized coffee table, and weighed in at 120kg and still it got the heat sinks up to 60c after 3hrs and proceeded to get the dreaded class A thermal runaway, plus I had to change the power points to industrial ones because it started to melt the standard house ones.
The only way to keep it cool was to fan force x 4 the massive heat sinks, but this was too noisy. After this amp I built the same but this time I water cooled it, first one was self contained recirculated water with a quite pump heat sink jacket mini radiator and fan, it looked weird but worked a treat, wish I had photo's of it (still weighed in 60kg. After this one there were 2 more both water cooled but using the house water and draining into the garden.
This unsound is why I am confident in what I say about the pseudo pure class A amps out there, and why you should study the link to the Mark Levinson ML2 mono blocks I posted earlier and see what it takes to get 25w of A class, and they get too hot to touch
Cheers George |
Goergelofif, the Krell KSA 80 and KSA 200 (and their mono counterparts the KMA 160's and KMA 400's) preceded the KSA 250 by a couple of years and were of different design generations.
http://www.krellonline.com/history.html |
The mighty Karans are most certainly up there with the very best if you're into natural sounding SS. |
|
I thought the Plinius SA-Reference which claims 2x100W Class A was already quite a big claim, but has anyone seen a Karan S400 which claims to deliver 470W x 2 Class A in an even smaller chassis! |
Same topology Unsound, just different models in the same rang as the KSA250 range, all with partial Class A not even 30% of their full output into 8ohms.
Like I said the only ones to have high % of Class A compared to rms output, was the fan forced Krells of 80's.
And after that the only model to get near them with good amount class A % was the Plateau Biasing (Anticipator Circuit) Krells "S" models with their Xmas tree bias lights, but they never sounded as good from many a report.
Cheers George |
Another vote for Clayton Audio S100, M-200 and M-300. |
I received my pair of Pass XA100.5's a short time ago and I'll toss my vote in for the Pass XA series. |
I was referring to the Krell KSA 80, KSA 200, KMA 160, KMA 400s. |
Yes but they were only quite low in Class A
For instance the massive KSA-250 with all it's heatsink could only do 28.5 watt Class A into 8ohms and then up to 250watts of Class B into 8 ohms. And these ran stinking hot.
http://www.stereophile.com/content/krell-ksa-250-power-amplifier-when-class-class
Cheers George |
Goerge, Krell had some Class A amps sans fans before Plateau Biasing, yes, with copious heat sinks. Still amongst my favorites. |
03-02-12: :Manitunc. Those amps don't use as much power when idling and don't get quite as not. My Dussun V6i, Musical Fidelity M3, Nobis Convigore and Classe 100 all run that way and sound pretty good. Manitunc:
If they don't run hot then they are not biased very high into Class A, maybe just a few watts depending on heatsink area.
"Ohms Law" simply put for the non technical to understand,
A 25 watt "only" pure class A biased amp needs X amount of heatsink area as the ML2's have I posted the link to.
A 100-150watt class a/b amp with 25watts of pure Class A bias needs up to 4 x the amount of heatsink area, even though the class A is the same as the ML2's, because the rail voltages are so much higher for the extra a/b watts, this quadruples the heat, even though it's still only 25 watts Class A.
Then there's the sliding (Plateau Biasing) Class A amps like Krell developed, but they were never as good sounding as their Pure Class A classics, like the old KSA50 KSA80 and KSA100 monoblocks all with fan forced cooling with no external heatsinks, just chimney's inside with fans at the bottom.
Cheers George |
there are a few amps that run Class A up to between 10 and 25 watts before switching to Class A/B. But 25 watts in a 90db efficient speaker is about 103db, which is pretty loud on an average. In fact, at normal listening levels, you might not hit 103db even on peaks or heavy bass notes. Those amps dont use as much power when idling and dont get quite as not. My Dussun V6i, Musical Fidelity M3, Nobis Convigore and Classe 100 all run that way and sound pretty good. |
Geoegelohi,
Great job! I am sure it sounds incredible. My next step is building some speakers. |
"Goes to show that others are stretching a long bow when they quote class a figures"
Amen. |
