h_a said:
I'm really wondering why this legend still survives
I'm not aware of any popular ClassA amp that has constant current draw.*
Every push-pull ClassA amp, even single-ended designs as the Alephs do not follow this 'rule'.
Have fun, Hannes
*sorry I do not have any clue about tube gear, so maybe I'm missing a lot of these.
EDIT: maybe one of Nelsons early Zens draws constant current.
Here is what I think is the reason for the confusion. It is perhaps a matter of semantics.
The proper thing to say is that the POWER draw of an amplifier when in class A is constant. This is very different than saying that the current draw from any given rail is constant.
The other important good thing about class A that is linked to this is that the current draw from the rail is sinusoidal if the signal is sinusoidal. This means that there is little or no opportunity for coupling nasty half wave rail currents, with a huge spray of harminics, into other circuitry or into the grounds.
If you believe that EMI is an important concern for sound quality, class A is a great way to get rid of a huge local source of it.
Cheers,
Bob
Of course we do have examples of truly constant draw - Single-ended
class A biased by a constant current source. My F2 and the original Zen
have one rail, are capacitively coupled to the output, and have a
constant current draw.
Push-pull balanced Class A designs can also make that claim.
class A biased by a constant current source. My F2 and the original Zen
have one rail, are capacitively coupled to the output, and have a
constant current draw.
Push-pull balanced Class A designs can also make that claim.
john curl said:
Hi John,
I agree completely. The crest factor of well-recorded music is quite high, so indeed a great percentage of the listening experience will be in the class A range you describe.
Although high-biased class AB carries with it some risk of gm-doubling distortion, that distortion will tend to come into play at higher power levels, at signal current transitions that are further removed from the zero crossoing. Conventionally "optimally-biased" class AB amplifiers have the transition ocuuring right in the middle at low signal levels.
A lot of this also underlines the importance of not quoting just lumped THD measurements, but rather paying attention to the spectrum of those distortion products AND at what power levels they make their appearance.
Because many THD analyzers cut off at about 80 kHz (mine cuts off at 200 kHz), and because HF distortion tends to be more of a problem, I tend to prefer the 19+20 kHz CCIF test with spectrum analysis, so that higher-order distortion products plainly come through.
Cheers,
Bob
Hi Grey,
I like that saying, because it is so true. Using too many class A designs will force all amplifiers except class D to be outlawed at some point in time. Just kidding.
Now, instead of taking the easy way out for a low distortion design, why not accept a challenge and work on more energy efficient amplifiers?
Disclaimers:
1. No, I'm not one of those eco-people. I wear shoes, not sandals.
2. I'm not suggesting everyone go for class "D" designs. Just more reasonable designs as far as dissipation per watt is concerned.
3. I accept that heat is the enemy to all electronic circuits (and most solids for that matter - or anti-matter!).
4. I like big cars or trucks. They aren't that bad on gas and they last longer than pip-squeak cars. There is an energy cost to create and destroy vehicles too. I also really like the idea of an external crumple zone
-Chris
Okay, that's your viewpoint. It works for you just fine, but there will come a time when energy costs will rise to a point where most of the population will not accept the costs of running these amplifiers. There also must be some acceptance for the impact to the environment. Right now, you seem to be in the mind set where "no one single snowflake in an avalanche ever feels responsible".
I like that saying, because it is so true. Using too many class A designs will force all amplifiers except class D to be outlawed at some point in time. Just kidding.Except in the summer when it is a clear liability. Even up here in Canada, believe it or not.
Now, instead of taking the easy way out for a low distortion design, why not accept a challenge and work on more energy efficient amplifiers?
Disclaimers:
1. No, I'm not one of those eco-people. I wear shoes, not sandals.
2. I'm not suggesting everyone go for class "D" designs. Just more reasonable designs as far as dissipation per watt is concerned.
3. I accept that heat is the enemy to all electronic circuits (and most solids for that matter - or anti-matter!).
4. I like big cars or trucks. They aren't that bad on gas and they last longer than pip-squeak cars. There is an energy cost to create and destroy vehicles too. I also really like the idea of an external crumple zone
-Chris
anatech said:
Untrue. Not that I've made a big deal out of it, but I'm heading towards a solar powered system in the long run. The most obvious line of sight for solar cell arrays in my yard is blocked by trees, but at the rate trees are dying around here (I bought a 2 3/4 acre wooded lot in 1995--I estimate that I've lost roughly a third of my trees since then due to the enduring drought [Feb rain fall normal = 3.93"...so far this month = 0.55"]), that line of sight will be clear within the next three to five years. Don't preach to me of environmental concerns. I am far more aware of them than my neo-conservative neighbors. Possibly moreso than you.
Did I mention that my listening room is in the basement and that even in the summer it doesn't go above 72 degrees or so? I don't bother air conditioning my basement. So, no, I'm not working uphill against the air conditioning. In fact, there are times in the summer when it's a little on the cool side in my listening room.
Good try, though.
Grey
Hi Joshua_G,
I'm working on a "power diamond buffer" type output stage, CFP. It's showing promise. The concept I gave you tells you almost everything you need to know, it's stone simple. I have prototypes out in the field from 2004. No failures, even with the worst case components in one channel of each.
What are you designing? Have you built anything in an amplifier from your own imagination yet?
Hi Grey,
Most of what I posted was light hearted tongue-in-cheek.
To be honest, you may be far more ecologically aware than I am. I don't know and I have no way of knowing. This might bother me if I cared, but I don't. I just threw the idea out there. It is but one example of the many ways we waste energy.
However, my point was that most all the other people who have bought your designs, or any other class A products, are fighting their air conditioning. The human animal being what it is, they just want what they want and to heck with everyone else. Compared with the amount of energy you use, your numbers aren't even visible in the total.
Ah heck, I wasn't trying anything. I was just pointing out the fact that resources are being wasted, while we still have them. Do you know that some power plants burn coal or natural gas to generate electricity? Therefore, class A designs are responsible for the burning of some fossil fuels.
Grey, I was having a little bit of fun with you. I didn't intend any ill will at all. It was just an opportunity to poke fun with an extreme example of amplifier dissipation for very few average audio watts out.
Guilty conscience? Kidding!
-Chris
First, try and work on thinking up your own retorts. You copy John and others often enough so that I am unsure if you have your own personality. Besides, I wasn't even attacking anyone, so what's your problem with life?
I'm working on a "power diamond buffer" type output stage, CFP. It's showing promise. The concept I gave you tells you almost everything you need to know, it's stone simple. I have prototypes out in the field from 2004. No failures, even with the worst case components in one channel of each.
What are you designing? Have you built anything in an amplifier from your own imagination yet?
Hi Grey,
Most of what I posted was light hearted tongue-in-cheek.
Not with powerful class A designs you aren't!
Good show. I hope you realize some capital gains there. You need more tree though. Mind you, it might make a nice putting center after those trees die out. Only a few more years to go.
I wasn't preaching, but those concepts are important on a global scale. But if you are aware of those concepts and by extension, aware of the farther reaching impacts of your work, does that make you evil? An evil scientist complete with Joshua_G as "mini me"? Sorry. bad joke, but it struck me as being funny.
To be honest, you may be far more ecologically aware than I am. I don't know and I have no way of knowing. This might bother me if I cared, but I don't. I just threw the idea out there. It is but one example of the many ways we waste energy.
No, you didn't. I had no idea as a matter of fact. I will probably have forgotten that fact by tomorrow, but I do have one question for you. Grey, do you have flood insurance?
Whew, that's a load off my mind. I was worried about your own energy bills in the summer.
However, my point was that most all the other people who have bought your designs, or any other class A products, are fighting their air conditioning. The human animal being what it is, they just want what they want and to heck with everyone else. Compared with the amount of energy you use, your numbers aren't even visible in the total.
But .... but .... but.
Ah heck, I wasn't trying anything. I was just pointing out the fact that resources are being wasted, while we still have them. Do you know that some power plants burn coal or natural gas to generate electricity? Therefore, class A designs are responsible for the burning of some fossil fuels.
Grey, I was having a little bit of fun with you. I didn't intend any ill will at all. It was just an opportunity to poke fun with an extreme example of amplifier dissipation for very few average audio watts out.
Guilty conscience? Kidding!
-Chris
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