Going Big class A?
- Thread starter awsmone
- Start date
No, it will not. And it is very easy to understand why. The output devices in class A amps by definition never turn off and it is the bias current which determines the maximum current output before one of the output devices turns off. And this maximum current is exactly fixed by the bias current at 2 x Ibias. As power is proportional to the current (which is limited by definition to 2 x Ibias) and inversely proportional to resistance, it is obvious that each halving of speaker impedance will cause halving of class A power.
This has nothing to do with AB power, which for a massively built amp generally doubles with halving of impedance.
The above is not a speculation, or an approximation: unless class A is based with a variable bias scheme, like Krell's "sustained plateau" there is just no way to avoid it.
Substantially increasing the obfuscation of this subject is the addition of the term "peak class A power" in addition to RMS power. This i would rather not comment, but most manufacturers seem content with quoting just the RMS figure.
Surely not you or I , Peter.
What is curious is that Nelson Pass answers your question in the article you refer. I quote from it:
"Push-pull amplifiers generally operate in Class A mode up to a point where the output current is twice the value of the bias current. "
Now P = IxV , V = IxR -> P = IxIxR. If I stands constant what happens to P when R decreases?
The important point is that independently of the referred numbers your amplifiers have a much higher bias than average amplifiers of similar power - so you will be listening more in class A with them than with most other amplifiers using the same speakers.
Just a recent link (tropic): https://www.stereophile.com/content/pass-laboratories-xa2008-monoblock-power-amplifier
Output's percentage of THD+noise reaches 1% (1kHz)—
the Pass Labs XA200.8 amplifier clipped at:
• 258W into 8 ohms (24.1dBW)
• 480W into 4 ohms (23.8dBW)
• 700W into 2 ohms (22.4dBW)
North Star what is your point here. Please tell me your kidding if you think the amp clipping means it’s in class a
Has here ever been an amp that has that many watts on class a much less the figure in watts grows at lower impedance
That’s at a class A/B please not you too.
I have read and was told of some who just refuse to to take the time to understand the posts. In fact how about the nae sayers google the questions on what class a means this is beyond rediculas at this point
Class a means the amp is biased to be on so it’s actually producing current to itself in a way at idle. So max class A can only be what it’s biased at. A simple rule of thumb is 25% is a usable class a value to judge by
It’s hard to follow posts that have no factual based ideal values.
Anyway you guys have worn me out and micro let this go you cannot inform those who don’t read comments as to why.
One last comment. Read Lamms website don’t you find it odd they use our comments and the rest don’t. Goodnight guys I wish an admin would jump in this to maybe then make the nays feel better about being wrong
Has here ever been an amp that has that many watts on class a much less the figure in watts grows at lower impedance
That’s at a class A/B please not you too.
I have read and was told of some who just refuse to to take the time to understand the posts. In fact how about the nae sayers google the questions on what class a means this is beyond rediculas at this point
Class a means the amp is biased to be on so it’s actually producing current to itself in a way at idle. So max class A can only be what it’s biased at. A simple rule of thumb is 25% is a usable class a value to judge by
It’s hard to follow posts that have no factual based ideal values.
Anyway you guys have worn me out and micro let this go you cannot inform those who don’t read comments as to why.
One last comment. Read Lamms website don’t you find it odd they use our comments and the rest don’t. Goodnight guys I wish an admin would jump in this to maybe then make the nays feel better about being wrong
Yes, Bob, even JA had doubts at 8 ohm ...
"Although Pass Labs specifies the XA200.8 operating in class-A, I suspect that even with its massive heatsinking, the amplifier doesn't have sufficient bias current to allow class-A operation up to its specified maximum power."
Read more at https://www.stereophile.com/content...er-amplifier-measurements#SETjZB3153fcVBeR.99
Al, I simply posted a small quote sample from the measurements page from that review of the Pass Labs XA200.8 Class A mono power amplifier. It doesn't say in the measurements when class AB starts to kick off.
Francisco quoted John Atkinson who also doesn't know, he suspects...insufficient bias current for real Class A operation.
All I know is that it's a Class A specified mono amp.
• https://www.passlabs.com/amplifier/xa200.8
?https://www.dagogo.com/a-pass-labs-...-pure-class-a-high-current-monoblocks-review/
* I can ask Nelson Pass.
Edit: I just did. I'll check in the next 24 hours or less for a reply.
Francisco quoted John Atkinson who also doesn't know, he suspects...insufficient bias current for real Class A operation.
All I know is that it's a Class A specified mono amp.
• https://www.passlabs.com/amplifier/xa200.8
?https://www.dagogo.com/a-pass-labs-...-pure-class-a-high-current-monoblocks-review/
* I can ask Nelson Pass.
Edit: I just did. I'll check in the next 24 hours or less for a reply.
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Ty north Starr , we both know he can’t say what’s correct. it’s going against what it’s advertismet states
The fact he says he does not not think so in the review Is the clue lol. A reviewer must walk a line and never cross it
Leaving bread crumbs for those who understand it is enough without crossing that line.
Atleast I feel better in that you did not have malice at this topic and my posts. I doubt he will answer you correctly as it’s his product. Years ago chord electronics made a dac called the HUGO. It was touted as a giant killer
For me it was not good and it’s pcm was better than it’s dsd again for me.
The lead designer of it ROBERT watts was active on threads about it.
In a heated discussion I pointed out how bad it’s dsd was. He at this point became very honest
He said dsd sucks and so does analog and only pure pcm was a good recording medium lol while he did not say suck. He did with nice detail mean this very clearly.
The thread got locked I was banned and both his and my comments were removed.
A designer or maker cannot be truly honest in forums
As advertised virtues can be exposed as false. Pass labs makes great products this is a given. But to sell we need something that’s above most. Be it class a or how much it weighs or it can power a 1 ohm load
It’s ok to push things in my view coz when we buy most all want to feel they got the exceptional product. Very few buy used like me and even less want the best sound by matching it all. Now I am not saying most don’t know good sound either.
And many speakers and Amps work well tougher. In my case I have speakers that kill amps and needed an amp that can do justice for them. Many amps made can play my speakers but only a handful ever made do them well.
The fact he says he does not not think so in the review Is the clue lol. A reviewer must walk a line and never cross it
Leaving bread crumbs for those who understand it is enough without crossing that line.
Atleast I feel better in that you did not have malice at this topic and my posts. I doubt he will answer you correctly as it’s his product. Years ago chord electronics made a dac called the HUGO. It was touted as a giant killer
For me it was not good and it’s pcm was better than it’s dsd again for me.
The lead designer of it ROBERT watts was active on threads about it.
In a heated discussion I pointed out how bad it’s dsd was. He at this point became very honest
He said dsd sucks and so does analog and only pure pcm was a good recording medium lol while he did not say suck. He did with nice detail mean this very clearly.
The thread got locked I was banned and both his and my comments were removed.
A designer or maker cannot be truly honest in forums
As advertised virtues can be exposed as false. Pass labs makes great products this is a given. But to sell we need something that’s above most. Be it class a or how much it weighs or it can power a 1 ohm load
It’s ok to push things in my view coz when we buy most all want to feel they got the exceptional product. Very few buy used like me and even less want the best sound by matching it all. Now I am not saying most don’t know good sound either.
And many speakers and Amps work well tougher. In my case I have speakers that kill amps and needed an amp that can do justice for them. Many amps made can play my speakers but only a handful ever made do them well.
Bob,
Here we go again. Real class A is too generic to be of any value. An amplifier can be class A is some conditions and class AB in others. Unless you refer to all the relevant parameters and are very specific such claims can not be judged. Your omission of "up to its specified maximum power" completely changes JA sentence!
Class A is a mode of operation. For a defined amplifier operation in this mode depends on load impedance and power - it is a bi-dimensional graph, and should be judged looking at the needs of a speaker and user.
Unfortunately the impedance is a complex curve, not a constant, with peaks and dips at frequencies that can need or not a lot of energy. As usually we do not have this data, we write generic theoretic posts on class A and must use our ears to choose our systems. But in order to listen we must get attracted to the speaker - and as people love technical motivation, manufacturers try to supply it.
The measurements for power were made @ 1kHz.
To me real life audio is 20Hz to 20kHz.
The full review is what I posted first. I know the members here would take the time to read it in its entirety, about ten minutes, more of less, then look @ the measurements and conclude the results.
We are talking Class A operation up to its point of maximum real life power.
Nelson Pass is a great designer and great people; let me look in the next hour or so if he replied to me, from diyaudio forum where you too are a member.
* The XA200.8 is a very impressive amp, in & out. It's not cheap but needed for serious music listening quality from the best loudspeakers that demand nothing but some of the stable best.
I wish I could afford few pairs to biamp or triamp. I need a room build inside an iceberg, very frigid.
EDIT: http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier-1591.html#post5500201
To me real life audio is 20Hz to 20kHz.
The full review is what I posted first. I know the members here would take the time to read it in its entirety, about ten minutes, more of less, then look @ the measurements and conclude the results.
We are talking Class A operation up to its point of maximum real life power.
Nelson Pass is a great designer and great people; let me look in the next hour or so if he replied to me, from diyaudio forum where you too are a member.
* The XA200.8 is a very impressive amp, in & out. It's not cheap but needed for serious music listening quality from the best loudspeakers that demand nothing but some of the stable best.
I wish I could afford few pairs to biamp or triamp. I need a room build inside an iceberg, very frigid.
EDIT: http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier-1591.html#post5500201
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I swear last time I answer in this topic not to offend but I feel offended now.
He knows it’s wrong he knows it’s false advertising. The sad part is he cannot say it is due to all else who bloat real measurements to make there products apear to do what no other product can. Facts are in the review I posted he says it’s apears it not biased enough
Your comment is he does not know. No you and others who interpret him as not knowing don’t
It’s funny really nelson pass some stuff to make his amps sound as they do it’s not magic it’s designed to be this way.
My amps idle at 9 amps each that’s at 125
Volts that’s 1125 watts and still in the end I am 140 watts pure real class A
So how can his be more it’s just wrong man. My amps can deliver 60 amps continues into 1 Ohm weigh 350 pounds each
Is pass a Magician now. It’s just false and he cannot say it’s not and anyone who thinks it’s even close is not understanding of the basic amp topology. Anyway I am going guys not more class a enjoy the amp no matter what you think it is.
He knows it’s wrong he knows it’s false advertising. The sad part is he cannot say it is due to all else who bloat real measurements to make there products apear to do what no other product can. Facts are in the review I posted he says it’s apears it not biased enough
Your comment is he does not know. No you and others who interpret him as not knowing don’t
It’s funny really nelson pass some stuff to make his amps sound as they do it’s not magic it’s designed to be this way.
My amps idle at 9 amps each that’s at 125
Volts that’s 1125 watts and still in the end I am 140 watts pure real class A
So how can his be more it’s just wrong man. My amps can deliver 60 amps continues into 1 Ohm weigh 350 pounds each
Is pass a Magician now. It’s just false and he cannot say it’s not and anyone who thinks it’s even close is not understanding of the basic amp topology. Anyway I am going guys not more class a enjoy the amp no matter what you think it is.
Nelson Pass replied to my question an hour ago...11:08 AM
See his attachment from his post...link above.
* Al, are you also a member @ diyaudio forum? Perhaps you can have a conversation with Mr. Pass and we can learn more. To be honest I could use some extra learning knowledge, I'm always thirsty for new discoveries.
See his attachment from his post...link above.
* Al, are you also a member @ diyaudio forum? Perhaps you can have a conversation with Mr. Pass and we can learn more. To be honest I could use some extra learning knowledge, I'm always thirsty for new discoveries.
Let’s assume his specs are factual your climax are an increase of watts as imp
Goes down
This means about 100 watts at 4 ohms didn’t your post say something way above 200 at 4 ohms ohms
Either way his figures work out of in fact the amp does idle st that usage level
The point still stands it’s halved watts as imp is halved not more
Do you forget that part lol.
I won't be pushing it either. I asked honestly my question and he replied to me with grace, a Nelson Pass' trademark.
One word (Extra Class A - XA200.8): Heat.
___
My post simply referred to the measurements.
* You need a good electrical grid in your home, and a cold room.
Tube amplifiers you don't leave them alone when turn on and operating.
I would say the same with solid state Class A amplifiers.
One word (Extra Class A - XA200.8): Heat.
___
My post simply referred to the measurements.
* You need a good electrical grid in your home, and a cold room.
Tube amplifiers you don't leave them alone when turn on and operating.
I would say the same with solid state Class A amplifiers.
Maybe it’s just me but his math given does not add up but that’s another story he seems to be mixing facts and fiction all
In peak current 7.4 amps then 4 amps bias per side
Peak is 1.414 of rms so 7.4 is 5.23 amps rms per side since bias is dc
So he seems to get more out of less. A magician like I said. Lol. Good by buys.
Thanks Bob. Nelson Pass answer says it all:
" The output is rated at 200 watts into 8 ohms, and the amplifier is rated Class A to this figure.
We have now elements enough to draw the complete class A versus impedance graph of this amplifier.
This means approximately 100W at 4 ohm and 50W at 2 ohm (resistive load) . Considering that the impedance of a speaker is a complex number, real power in class A can be lower than that.
Fortunately he also confirmed that "430 watts peak, which is 215 watts rms" so now the pseudo-facts become the truth.
No Al, I think Nelson is correct. This 7.4 amps is not related at all to RMS, but is a conservative version of 2x4 amp.
From : https://www.passlabs.com/press/leaving-class
"Push-pull amplifiers generally operate in Class A mode up to a point where the output current is twice the value of the bias current. "
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