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HAYK
Simulate one and you will see how it is so difficult in feedback loop to generate more even orders by a single stage than the odd orders of all other stages combined.
It is not the lower harmonic distortion that sucks the "magic" out. With 24 dB GRND feedback the Zout of the amplifier is more like a SS amp and the way it drives speakers changes like night and day. Amplifiers with no feedback or moderate local feedback drive speakers in a different way and that's where "magic" is. Also the impact of a certain amount of GRND feedback on Zout is NOT the same as the same amount of local feedback, in general.
It's not harmonic distortion which below a certain value, say 3% at nominal rated power, becomes pretty much irrelevant on its own if output power is high enough (say 5-8W or more, depending on the speakers' efficiency). Why I did write 3%? Because that is more or less the physiological threshold at 90 db SPL for most people. For some it might be a bit less but it won't be an order of magnitude less ( i.e. 10x). A valid reason to keep THD at lower level is to minimize IMD but again below a certain threshold there is not much to gain....
So in the end there is a balance of all things to look at. Just speculating on THD spectra does not bring anywhere in my opinion.
It's not harmonic distortion which below a certain value, say 3% at nominal rated power, becomes pretty much irrelevant on its own if output power is high enough (say 5-8W or more, depending on the speakers' efficiency). Why I did write 3%? Because that is more or less the physiological threshold at 90 db SPL for most people. For some it might be a bit less but it won't be an order of magnitude less ( i.e. 10x). A valid reason to keep THD at lower level is to minimize IMD but again below a certain threshold there is not much to gain....
So in the end there is a balance of all things to look at. Just speculating on THD spectra does not bring anywhere in my opinion.
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I try to design tube amplifiers, that have circuits that intrinsically are:
low distortion, have good frequency response, good square wave response, and larger than unity damping factors, without using global negative feedback; and that are affected as little as possible by the signal source at the input, and the load [loudspeaker] at the output.
I try, so of course they do not always meet those criteria.
And, I generally do not design them for medium or large output power.
Have fun designing, building, and listening!
low distortion, have good frequency response, good square wave response, and larger than unity damping factors, without using global negative feedback; and that are affected as little as possible by the signal source at the input, and the load [loudspeaker] at the output.
I try, so of course they do not always meet those criteria.
And, I generally do not design them for medium or large output power.
Have fun designing, building, and listening!
For me personally, it never made sense to completely remove "all" distortion from a tube amplifier.
The whole reason to use tubes in my personal opinion, is to enjoy the tube distortion (or a tube amplifier rather, there are more things to it!)
So I rarely add more than about 6dB of feedback.
For me, I purely enjoy it as nostalgia.
Just giving the idea of being back in the 50s,60s,70s (early 80s?) with some properly matched loudspeakers with it.
No that isn't "perfect" sound reproduction, but just pure nostalgic enjoyment.
I guess there is one exception to this, which is when the whole amplifier is extremely well done an the tube amplifier is just considered as a work or art to look at. So basically acting like a modern very low distortion amplifier.
Because tubes/valves just look a billion times better than just a blob that amplifies with the lowest distortion thinkable.
But I wouldn't use that as my daily driver, the convenience of modern equipment is just to nice and easy for that.
The whole reason to use tubes in my personal opinion, is to enjoy the tube distortion (or a tube amplifier rather, there are more things to it!)
So I rarely add more than about 6dB of feedback.
For me, I purely enjoy it as nostalgia.
Just giving the idea of being back in the 50s,60s,70s (early 80s?) with some properly matched loudspeakers with it.
No that isn't "perfect" sound reproduction, but just pure nostalgic enjoyment.
I guess there is one exception to this, which is when the whole amplifier is extremely well done an the tube amplifier is just considered as a work or art to look at. So basically acting like a modern very low distortion amplifier.
Because tubes/valves just look a billion times better than just a blob that amplifies with the lowest distortion thinkable.
But I wouldn't use that as my daily driver, the convenience of modern equipment is just to nice and easy for that.
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I am quite sure that in the 1950s, there was more than one model number of amplifiers that had 0.1% THD.
Nostalgia is great!
So is real good engineering!
When you are listening to amplifiers, old or new designs, please remember to consider all the different vintages of loudspeakers.
The key word for playing back music is "System".
Then, we have the turntable & cartridge; tape recorder playback; CD; etc.
This is also part of the System.
Microphone, Studio, post production house, Vinyl, tape, CD, etc.
System.
A fun event is when an audio club has an Audio Crawl:
3 groups of audiophiles (~ 15 people) gather together and get the directions to 3 club member's houses (the hosts of the crawl).
5 in a group, x 3 homes, and round robin rotate 3 times = 15 people hearing 3 hosts' systems. Bring a vinyl or CD to play a number.
But please do not bring the Telarc 1812 Overture, that 6Hz canon is not fair to your hosts.
After the crawl, everybody goes to a restaurant and compares notes (mostly just discusses how fun it was, and how good the hosts' systems sounded).
(As far as I know, I was the first to invent and implement the 'audio crawl', many decades ago).
Another very fun and interesting event is a properly designed double blindfold listening test.
Compare 2 amplifiers, or 2 loudspeakers, or 2 phono cartridges, etc.
Please do not get stuck in audiophile boredom.
Lighten up, and Enjoy the Music.
Everything is what it seems to be, until you find out it is different
Nostalgia is great!
So is real good engineering!
When you are listening to amplifiers, old or new designs, please remember to consider all the different vintages of loudspeakers.
The key word for playing back music is "System".
Then, we have the turntable & cartridge; tape recorder playback; CD; etc.
This is also part of the System.
Microphone, Studio, post production house, Vinyl, tape, CD, etc.
System.
A fun event is when an audio club has an Audio Crawl:
3 groups of audiophiles (~ 15 people) gather together and get the directions to 3 club member's houses (the hosts of the crawl).
5 in a group, x 3 homes, and round robin rotate 3 times = 15 people hearing 3 hosts' systems. Bring a vinyl or CD to play a number.
But please do not bring the Telarc 1812 Overture, that 6Hz canon is not fair to your hosts.
After the crawl, everybody goes to a restaurant and compares notes (mostly just discusses how fun it was, and how good the hosts' systems sounded).
(As far as I know, I was the first to invent and implement the 'audio crawl', many decades ago).
Another very fun and interesting event is a properly designed double blindfold listening test.
Compare 2 amplifiers, or 2 loudspeakers, or 2 phono cartridges, etc.
Please do not get stuck in audiophile boredom.
Lighten up, and Enjoy the Music.
Everything is what it seems to be, until you find out it is different
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