Historical look at amps

How do you figure it has to do with stabilising?? Stabilising what?

And which way do you use for marketing, and which for precision? By precision, do you mean THD numbers of 0.00001%? Seems to me that is done for marketing, as the amps in the mid-70s using that approach sounded rotten.

Some of us design it so that it sounds best to us. Whether others agree or like it is another matter. ("Some" being most every amp designer that I know.)

Keis, you opened Pandora's box here & I expect there to be some heated debate! :-) This topic can degenerate into a "religious" battle.

Anyway to answer a few points:
Jameswei - nice cut & paste from your Aleph owner's manual. Show that there are so many diff ways to say the same thing & that there doesn't seem to be any consistency in the audio industry. They use whatever terminology that sells the most equipment!
Search thru that manual (I've read the X series manuals on-line & I know that it exists in there FOR SURE) & see if you can find this quote from Nelson Pass: "I ask anyone to show me an electronic circuit & I will show them the feedback path".

Which leads me, nicely, into my next point:
Keis: you are DEAD wrong when you say that Ayre circuits have zero feedback! Sorry to be so blunt but this topic has been dealt w/ here on Audiogon N number of times. Just search the archives! Member Aball nailed it quite well - "The marketing gurus have done a great job of convincing audiophiles that zero feedback is the way to go but no functional amplifier design actually exists without any feedback".
Precisely correct!
This is also corroborated by member Gregm post about stabilizing.
Ar_t asks "stabilizing what?" Stabilizing the transistor bias point. This is of utmost importance - the bias point. Shift the bias point puts a transistor in Class-A or class-AB or Class-B or Class-C or Class-D, etc. When designing any electronic circuit, be it vacuum tube or s.s. - the designer spends 70% or more of their time ensuring that the bias point of the device(s) is(are) correct for the intended application & that the device will remain in class-A/AB/B/C/D, etc over the entire signal excursion. If the bias point is not stabilized, the device drifts with input signal (called signal level distortion, which is a really bad thing) & you can hear it.

No electronic circuit on Planet Earth exists w/o negative feedback! however small the negative feedback, it's always there. To that effect, the Ayre circuits probably use local feedback either around an individual device or around a small cluster of devices. I don't know which but it's got to be one of these if they are claiming "zero feedback".

Whoever came up w/ IM distortion tests for audio amps must have done it to get good test-bench performance numbers 'cuz it's generally know that THD numbers & sonic performance have little or no correlation today. large amounts of negative feedback gave excellent test-bench performance but the amp sounded like sh$$ in a home stereo system. Amps having negative feedback usually lack macro-dynamics & they usually have a flat (2-D) soundstage. That's because the negative feedback loop allows only so much excursion of the transistor bias point before limiting it. The bias point is never allowed to leave a certain region (a very tight region if feedback factor is very high & a looser region if the feedback factor is low[er]) thus the transistor doesn't distort much & THD measures very well!

The reason for inserting negative feedback is that there was a very cool device that was invented in 1948 called the BJT! After several years of development & use in other areas, it was "ripe" for use in audio in the late 1960s & early 1970s. It was supposed to be the next revolution & was supposed to replace the venerable vacuum tube. Like sh$$!!!
The vacuum tube is a device whose operation can be described by oridinary physics (the stuff you learnt in high school) & from these equations you see that gain is a linear function of current & other physical parameters of the tube.
OTOH, the semiconductor transistor is a square-law (MOS) or an exponential law (BJT) device! Thus, the distortions produced by s.s. devices is totally diff from that produced by a linear amplification device (vacuum tube). There is much more odd order harmonic content in s.s. amplified music than there is in vacuum tube amplified music. Plus, owing to the non-linear relationship between gain & physical parameters of the s.s. devices, this distortion rises more rapidly than it does for a tube circuit. So, how to curtail this distortion?? You guessed it - negative feedback!
This negative feedback is our best friend when we are designing electronics for most all other applications EXCEPT audio because we want to do signal processing that is usually some means to an end other than critical listening.
However, for critical listening, negative feedback is our worst enemy. Makes the amp test & measure excellent but makes it sound like cr**!
It's taken us over 30 years to come to grips w/ this - slowly admitting it w/ each new generation of s.s. gear until we come to year 2004-2005 when manuf are openly advertising zero global feedback. What if there was some real intelligent designer back in the 1970s who realized the "hazardous" effects of negative feedback after a few releases of audio gear that had it & he spoke up against using it, I think that his business would have long gone under even tho he would have been correct!! It's taken us this long.
Today s.s. gear is making some real strides in sounding "real"......................very much like vacuum tube gear always did before it!!! LOL!
The transistor was to replace the vacuum tube - like hell it did! Just like CDs were supposed to replace vinyl!
Vacuum tube circuits still sound the best & any top-notch system has tubes in it. It'll always sound the best to a human ear as long as it remains a linear amplification device.
And, vinyl is more coveted today than it was during it hey-days.

What peeves me the most is that the users in the audio community are not as informed about electronics as they should be esp. if they are pre-disposed to spending large amounts of money on gear. The marketing dudes still seem to rule the roost & they still seem to twsit & turn details to enhance a sale & even brain-wash a user into thinking what THEY want the user to think.
Even more pissing off is when you try to spend some time to teach them, they come back & bite you! This move suggests to me that they want to remain ignorant. Well, ignorance is not a bliss......................it's ignorance!!
FWIW. IMHO.

Bombaywalla, that solid state most often uses feedback, may not be the perfect solution to a problem. On some level it works. On the other hand these problems are not the only ones that exist in audio amplification as we know it. All designs have problems that have less than perfect solutions. Yet, on some level they work. If a particular solution doesn't work satisfactorly for you, well, then you have options. Some may have measurable issues, that sound good enough for you. Some may have currently immeasurable issues that sound sound poor to you. Fine, but, "sh$$", "sh$$!!!" and "cr**!" is purely subjective and is also fine. To extrapolate that to mean that those who have made different choices than you, is due to ignorance is well, eh, ignorant. BTW, I plead guilty to some level of ignorance, but, I don't think I've been brain washed by the twists & turn of marketing dudes any more than I have been by this most recent post.

Unsound,
Read your post.
My post WAS NOT an attack on any person or persons. LET ME MAKE THAT CLEAR if it was not.
2ndly, I NEVER meant to say that my choices are better than yours (Unsound) or anybody elses. Let me MAKE THAT CLEAR as well, if it wasn't. (I should know better than that!)

You, Unsound, might not have been brain-washed by the marketing dudes, which is probably good for you. My statement was a general one. Most of the people fall for the marketing ploy & you often read posts supporting the marketing propaganda. Of course, there are people who have learnt & know better than to succumb to it.

Indeed what sounds "correct" to me might be/will be different from what sounds correct to someone else. I do find, however, that the longer a person stays in this audio hobby & gets many chances to hear diff gear & make direct comparisons of s.s. vs. tube gear in the same system, the better are his/her chances of realizing the positive attributes of linear amplification devices over non-linear ampl devices. That person might still not want to own tube gear - fine! - but the realization does set in.
This point might have been missed by you?

I don't know of any designer that looks to feedback as a solution to bias stabilisation in a SS amp. Lowering noise, distortion and output impedance, yes. Increasing bandwidth and input impedance, ditto.

Maybe the guys who design tube gear do, but I don't hang around with any.

But since this was supposed to be about a "historical look at amps", and feedback...........let me ramble on some about the stuff that I have done.

Mid 80s.......overall feedback, but much less than usual. Maybe 10-20 dB.

Late 80s.....no loop feedback in the voltage gain stage, loop feedback for the outputs. (Similar to Stasis.)

Mid 90s.......no loop feedback anywhere.

Early 00s........"digital" amps. Tons of loop feedback.

Looks like we have come full circle.