The whole thing would be a no-brainer if class A didn't sound good. I mean, really, why would anyone choose class A? It's expensive, it's hot, it's heavy, it's bulky...absolutely everything weighs against it. Except for the sound quality.
I seem to recall having mentioned this before, but even class A amps can sound better. I built a couple of Aleph 2s (tip of the hat to Nelson for making the schematics available). Now, the Aleph 2 is a class A amp to begin with and sounds fairly good, but being unable to leave well enough alone, I spent a few days playing with the bias. The results: Lowered bias (but still class A) caused the amps to sound thinner, more hi-fi. Stock bias (~3A overall bias) filled out the sound and gave a better image. Increasing bias above stock improved the image further and gave even better sound quality. I compromised at about 10% over stock bias due to the fact I was using TO-220 output devices and didn't want to cook them. Enough people here have Aleph variants that this should be easy to replicate. It's even easier on a "normal" amp with a bias pot--just watch the heat dissipation.
Those who do not hear any benefit to class A are, as I said earlier, welcome to buy the cheapest, most efficient amp available. If it meets your needs, then be happy and go on to the next thing.
The topic of "sliding" bias circuits always comes up at some point. On the surface, they seem like such an elegant solution that it's hard not to be seduced by the idea. The devil, as always, is in the details. Bias changes a lot of things. Take heat, the very thing you're trying to get under control. As the temperature increases, so does the gain of the device. And if the gain changes, then everything changes, and not for the better. In operation the amp changes behavior depending on how loud you play it. Worse yet, it changes with the dynamics of the music. Then there's the circuit required to change the bias. No matter how fast it tries to change the bias, it is always a step behind. This takes on a literal interpretation when you see circuits that maintain a higher bias after a signal peak in the hopes of 'being ready for the next peak.' The idea works in the sense that music comes out, but it's a flawed solution.
Class D? Well, music comes out, I suppose you can say that for it. 'Nuff said.
The idea of using a small high quality amp in conjunction with a larger lower quality amp (Quad current dumping/Threshold Stasis) would seem to have promise, but the brute force amp always seems to impose more character on the signal than you'd like.
Negative feedback--long touted as the panacea for all ills--usually plays a supporting role in most efficiency schemes. This leads to some (e.g. Self/Slone) claiming that a class B amp with enough feedback can give both efficiency and sound quality. Enough has been said about the effects of excess feedback elsewhere that it's not worth wasting pixels here. Note that NFB alone isn't an energy-saver. It's used as a band-aid to repair the damage wrought by sundry efficiency schemes. Unfortunately, it's not without blame(less...er, sorry, shameless joke) in the sonic department.
Etc. etc. etc.
For every measure devised in an attempt to get class A sound quality out of a less power-hungry circuit, a new set of ills is unleashed on the world. Needless to say, the sales literature never mentions the problems, only the benefits. It's the next generation that admits, if only by implication, that there was anything amiss. Otherwise how could the new product be "New and Improved" if its predecessor was, in fact, already perfect.
And so it's left to class A to thunder across the landscape, scattering lesser designs before it. Dinosaur it may be, but it's still king.
Make fun of dinosaurs at your peril. They had a much longer and more successful reign than we puny humans have managed so far.
Grey
I seem to recall having mentioned this before, but even class A amps can sound better. I built a couple of Aleph 2s (tip of the hat to Nelson for making the schematics available). Now, the Aleph 2 is a class A amp to begin with and sounds fairly good, but being unable to leave well enough alone, I spent a few days playing with the bias. The results: Lowered bias (but still class A) caused the amps to sound thinner, more hi-fi. Stock bias (~3A overall bias) filled out the sound and gave a better image. Increasing bias above stock improved the image further and gave even better sound quality. I compromised at about 10% over stock bias due to the fact I was using TO-220 output devices and didn't want to cook them. Enough people here have Aleph variants that this should be easy to replicate. It's even easier on a "normal" amp with a bias pot--just watch the heat dissipation.
Those who do not hear any benefit to class A are, as I said earlier, welcome to buy the cheapest, most efficient amp available. If it meets your needs, then be happy and go on to the next thing.
The topic of "sliding" bias circuits always comes up at some point. On the surface, they seem like such an elegant solution that it's hard not to be seduced by the idea. The devil, as always, is in the details. Bias changes a lot of things. Take heat, the very thing you're trying to get under control. As the temperature increases, so does the gain of the device. And if the gain changes, then everything changes, and not for the better. In operation the amp changes behavior depending on how loud you play it. Worse yet, it changes with the dynamics of the music. Then there's the circuit required to change the bias. No matter how fast it tries to change the bias, it is always a step behind. This takes on a literal interpretation when you see circuits that maintain a higher bias after a signal peak in the hopes of 'being ready for the next peak.' The idea works in the sense that music comes out, but it's a flawed solution.
Class D? Well, music comes out, I suppose you can say that for it. 'Nuff said.
The idea of using a small high quality amp in conjunction with a larger lower quality amp (Quad current dumping/Threshold Stasis) would seem to have promise, but the brute force amp always seems to impose more character on the signal than you'd like.
Negative feedback--long touted as the panacea for all ills--usually plays a supporting role in most efficiency schemes. This leads to some (e.g. Self/Slone) claiming that a class B amp with enough feedback can give both efficiency and sound quality. Enough has been said about the effects of excess feedback elsewhere that it's not worth wasting pixels here. Note that NFB alone isn't an energy-saver. It's used as a band-aid to repair the damage wrought by sundry efficiency schemes. Unfortunately, it's not without blame(less...er, sorry, shameless joke) in the sonic department.
Etc. etc. etc.
For every measure devised in an attempt to get class A sound quality out of a less power-hungry circuit, a new set of ills is unleashed on the world. Needless to say, the sales literature never mentions the problems, only the benefits. It's the next generation that admits, if only by implication, that there was anything amiss. Otherwise how could the new product be "New and Improved" if its predecessor was, in fact, already perfect.
And so it's left to class A to thunder across the landscape, scattering lesser designs before it. Dinosaur it may be, but it's still king.
Make fun of dinosaurs at your peril. They had a much longer and more successful reign than we puny humans have managed so far.
Grey
Re: Re: Re: Re: Re: Re: Re: Class A because that's still the best available
yup I remember......but I'm little disappointed that you stay with that liliputan one.........even if I like this pic:
http://www.briangt.com/gallery/magura-40stepattenuator/PICT0092?full=1
Magura said:
Naah, I guess the pre's are wasting somewhat more, and there are 4 of them, though switching power between them as the need for the different inputs arise....but no input selector switch in the signal path 😎
And as for the NKT....I don't think 50W is adequate.....the stepper alone eats like 20W or soas it's got a big rotary switch to turn....remember ?
Magura 🙂
Edit: NKT, now also in red 😉
http://www.briangt.com/gallery/magura-40stepattenuator
yup I remember......but I'm little disappointed that you stay with that liliputan one.........even if I like this pic:
http://www.briangt.com/gallery/magura-40stepattenuator/PICT0092?full=1
Re: Re: Re: Re: Re: Re: Re: Re: Class A because that's still the best available
Now could you do me a favour and tell my GF that 😀
Magura 🙂
Zen Mod said:
Now could you do me a favour and tell my GF that 😀
Magura 🙂
lohk said:
Exactly! I have electric heat in a small apartment. I would prefer to heat my apartment with Threshold rather than baseboard heaters any day.
In the summer I switch to UCD out of necessity.
A Class A amp that lets me select the bias from the front panel would be wonderful. For simplicity, I'd be happy powering down the amp to effect the switch. Of course, the rational solution for that is build a set of low power Class-A amps for summer.
And I keep dreaming of a TAD horn system someday.
Re: Class A because that's still the best available
You are on a good point though. We are but human with limited resources. If we reason that power distribution and loudspeakers are responsible for perhaps 99% of waste, it becomes clear where our best efforts can be used.
Beware of what you expect from others.BrianEno said:
You are on a good point though. We are but human with limited resources. If we reason that power distribution and loudspeakers are responsible for perhaps 99% of waste, it becomes clear where our best efforts can be used.
Even if we design more efficient devices it is always the operator that controls the outcome....There goes a few Carbon Credits.
http://www.msnbc.msn.com/id/19601277/
http://www.msnbc.msn.com/id/19601277/
Knock on wood that not everyone is into sound.
Vision the entire world population spending the summer break at Hawaii, simultaneously.
If 1 in a thousand is into audio and 1 of a hundred of those fancies Class A, all Class A lovers all around the globe would draw less than 10% of a single medium size powerplant's top output capacity.
(i suppose when it's an input/cascode/Vas/(pre)driver device, Class A biasing is not an antique ?)
There's another relic that survived the stone age living in California : the Tricholepidion Gertschi aka the Forrest Hill Silverfish.
(no offence, pa-p-ss)
Anyone of you also collected stones with these ex-fossil celebrity babes as a youngster ?
Vision the entire world population spending the summer break at Hawaii, simultaneously.
If 1 in a thousand is into audio and 1 of a hundred of those fancies Class A, all Class A lovers all around the globe would draw less than 10% of a single medium size powerplant's top output capacity.
(i suppose when it's an input/cascode/Vas/(pre)driver device, Class A biasing is not an antique ?)
There's another relic that survived the stone age living in California : the Tricholepidion Gertschi aka the Forrest Hill Silverfish.
(no offence, pa-p-ss)Anyone of you also collected stones with these ex-fossil celebrity babes as a youngster ?
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Well that sums up my point from the beginning, maybe (to)provocative but it's about weighing the pro's and con's of a certain designdecision. If there are a lot of con's with this technique, the ones you're summing so nicely, then the pro must be pretty decisive. You say Full Class A biasing is compulsory for obtaining the finest soundquality and that's what PassLabs is all about I think.
I just wondered why other highly respected designers of highend audio which have to make that same decision come up with other designs, with an other balancing point and still have the same objective as Nelson Pass to make superior sounding devices.
The mandatory consequence of your (and Nelson Pass's) claim is that the other designs (that are not fully Class A biased) are at least more compromizing and therefor inferior in that aspect to his products.
I understand the mechanism of advertising but I'm not having a discussion with Nelson Pass on a weekly basis about the designcriteria and the underlaying motivation why he chooses certain solutions in the field of audio-reproduction. The only way to derive some of that information is to read his statements in interviews, technical discussions, postings on forums and yes brochures too. That's the best effort I can make, those are communicationchannels where he expresses hisself. All other derivates like he's jiggling around with his patents so he can cook up some new schemes are speculative at least.
I had several sessions with friends where I would turn the biastrimmer on Rowland 7's, Threshold S/1000-SA/1, Rowland 8T, Levinson ML-3's up and down. Nobody noticed real differences except at low level listening when the quiescent current was almost nothing. This is not an attempt to refute your claim in anyway because technically speaking your completely right that the best way to keep a transistor behaving as lineair as possible is that sweet point on its loadline. It could though fit in the earlier stipulated equation what prize to pay to get the best possible and then you could reach a decision that culmunates in a product like a XA200.
Thanks for your extensive reply.
I have an electric heater with a fan. Thanks for helping me understand that the noise made by the fan is wasting energy😀
BrianEno,
I have read your posts from the beginning ang your arguments while clever are deceptively circular.
May I suggest you perhaps move your discussion to a Green Lobby group who will no doubt take you a little more seriously.
Perhaps an interesting point for your own awareness is that Pass Labs offers a range of commercial product in terms of scale of power and while NOT all of the models are fully biased for class A operation to the rated output.
Granted most of the diy designs here are fully biased and that is by choice and most are low powered versions.
But to suggest or imply for the premise of your statements that the sale, manufacture and distribution based on market popularity is the most powerful of the fully biased designs would be a gross misrepresentation of the facts.
I there find any notion of merit in your discussion flawed and totally invalid.
The Doctor
I have read your posts from the beginning ang your arguments while clever are deceptively circular.
May I suggest you perhaps move your discussion to a Green Lobby group who will no doubt take you a little more seriously.
Perhaps an interesting point for your own awareness is that Pass Labs offers a range of commercial product in terms of scale of power and while NOT all of the models are fully biased for class A operation to the rated output.
Granted most of the diy designs here are fully biased and that is by choice and most are low powered versions.
But to suggest or imply for the premise of your statements that the sale, manufacture and distribution based on market popularity is the most powerful of the fully biased designs would be a gross misrepresentation of the facts.
I there find any notion of merit in your discussion flawed and totally invalid.
The Doctor
How about a pool filter that consumes +10 MWh/yr if someone forgot the timer switch ?
Skip the 40KW gas heating and 0.5KW lights.
Special event for front row seat Energy star taggers : a dip in 35C preheated water on a windy -15C winter evening.
I wonder how many can afford a $44.5K XA200 ?
Fingers crossed i've saved enough for a Pass labs INTegrated-150 by now.
How's the Doctor amp coming along, Mackaluminium ?
Skip the 40KW gas heating and 0.5KW lights.
Special event for front row seat Energy star taggers : a dip in 35C preheated water on a windy -15C winter evening.
I wonder how many can afford a $44.5K XA200 ?
Fingers crossed i've saved enough for a Pass labs INTegrated-150 by now.
How's the Doctor amp coming along, Mackaluminium ?
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Dear Jacco,
Your entertainment factor is at the moment incredible (and I thought it couldn't be topped after you posted your comment on japanese symbols) 😀
Cheers, Hannes
PS: I admit this post may be a tad offtopic.
Your entertainment factor is at the moment incredible (and I thought it couldn't be topped after you posted your comment on japanese symbols) 😀
Cheers, Hannes
PS: I admit this post may be a tad offtopic.
h_a said:
ya'll be banned for that!
hehe- jacco obviously have cam as implant........... that's probably not power wasting ......... brain power instead NiMh........
BrianEno said:
175 lbs (the weight of an AX200) is a good reason not to decide to run things in class A. A very big part of those 175lbs is either transformer, capacitors or heatsinks....all very expensive stuff.
Even the AX200 have little work-arounds to avoid running "true" class A, in this case a dynamic constant curren source, which allows the whole thing to be about half the size of what it should have been at 20% efficiency of "true" class A.
Magura
The ironic thing no has mentioned yet is that the majority of "The Other" designers remained in the power number rat race for the last fifteen.
The most apparent reason to switch to sustained bias and low bias AB designing is to reach higher and higher continuous output power levels, without un-worldly weights and sizes, im-idiot-o.
And that, mes amis, has nada to do with quality of sound but is totally marketing driven.
I reckon NPapa might do rather nicely if he changed the name to Chipass labs and manufactured a bunch of 10lbs SuSy-LM amps.
After +20y of trying to learn the stuff i still don't manage to order at a Nippon restaurant, you care for my Japanese tutorials ?
INT-150 ?????
The most apparent reason to switch to sustained bias and low bias AB designing is to reach higher and higher continuous output power levels, without un-worldly weights and sizes, im-idiot-o.
And that, mes amis, has nada to do with quality of sound but is totally marketing driven.
I reckon NPapa might do rather nicely if he changed the name to Chipass labs and manufactured a bunch of 10lbs SuSy-LM amps.
After +20y of trying to learn the stuff i still don't manage to order at a Nippon restaurant, you care for my Japanese tutorials ?
INT-150 ?????
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