Historical look at amps


The amplifier evolution thread reminded me of the history of amplifier circuits that has occured over the last 20 years. Lots of changes but the one that stuck in my mind was the change in feedback circuits. In the early 1980s a good amp like Crown, McIntosh, Phase Linear etc all had large amounts of feedback and distortion levels of 0.00001% IM and THD. These amps sounded bad and the question was raised (and still is) why objective measurement didn't jib with listening tests. A Finnish engineer (OTTELA) came up with a new measurement called Transient IM Distortion (TIM). I wont go into the details but it did show that large amounts of feedback which made static IM and THD measurements good, made music waveforms bad. The result has been today's amps with low levels of global and local feedback, and better sound but with IM distortion levels of only 0.01% (and of course tube amps with more even then odd distortion harmonics). Just recently Ayre, and probably other companys are offering zero feedback designs. Feedback circuits have been with us since the 1920s and we are now just elliminating this basic design feature in modern amps and preamps.
keis

Showing 6 responses by unsound

Muralman1, while I can understand how you came to believe that Ar_t is "Expounding on a trait that is most damning", I believe that he has qualified that assertion.
As far as "class D amps on my (your) speakers." and "There are plenty of speakers, of all types being run by class D." in my previous post I said the jury is still out on the qualified generalization that Ar_t offered. Ar_t is entitled to his opinoin as much as anyone else here. I think my mention of sodium intake adressed that. Never the less it would appear that Ar_t may have more insight in these matters than most. Untill other manufacturers are as generous with their wisdom, we are unfortunately weighted in one direction. For that matter it sure would be nice if more users posted their experience as well. I'll take what's available and appreciate it. I'm not saying that any one is right or any one is wrong.
As far as why Ar_t doesn't build amps like Henry's, well, is Henry unable to keep up with the demand? I mean why would he? That's like saying why doesn't Krell make amps like c-j and visa versa. Ar_t has already said that his amps were originaly intended for the Home Theater crowd. He is obvioulsy found his market segment target. I may be extrapolating here, but, I suspect that Ar_t is himself surprised at how well this technology in his products overlap into the pure audio market and that perhaps there is an audience there as well.
I don't see any problem with Ar_t sharing his experience and qualifiactions. I think that's a good thing. As far as "I don't see any other amp builder doing that." Well I don't see many other amp builders posting here and that's a shame. I think it's in all our best interest to encourage this kind of input. That's the reason I'm posting this. I don't own and never have to my knowledge owned any of Ar_t's products. I have never met Ar_t. Before these recent Audiogon threads I never knew he existed. BTW, Ar_t has offered many compliments to other designers.
I think that Ar_t's opinon is that without the above mentioned designers skills these amps might have a tendency to be bright due to some inherent attributes. What may be lost is the compliment he is offering to these designers and their implamentations. This is something like the discussion on feed back in tradtional solid state amps. I'm not trying to re kindle a tube vs. solid state argument, but, this is much like the way that tube amp designers have had to work with and with out transformers in order to address those concerns that are more of an issue with that technology. That the qualtiy of an amp is system dependent seems to be accepted wisdom. Again the jury is still out on whether digital amps have a propensity for brightness. There is obviously a diference of opinion. My own very limted experience with digital amps raised this very question. I don't have enough experience to determine the answer.
This is not the first time poor Ar_t has had to deal with the issue of his business. Audiogon certainly isn't making it any easier. I don't believe Ar_t is trying to hide the fact, it just becomes redundant after a while. All the same for those not in the know, a heads up might be in order.
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.
Bombaywalla, perhaps the point was missed by me. As far as realization, others may indeed come to the same conclusion and others may not. How ever I think it important to realize that our systems are complex and some attributes of sound that may be particularly pertinent to an individual may be better served due to technical or budgetery needs to use certain components that that may be better served by alternate means of amplification. Just so we undertand each other, I don't take any personal offense by your opinion. I just thought that another perspective was in order. Best Regards.
Damn, we're really getting somewhere now. Thanks Ar_t! I love it when I actually learn something.
Muralman1, I have not done any serious listenig of digital amps, but, it is a characteristic that I have noticed on occassion. More importantly I think that Ar_t is suggesting that many if not most digital amps seem to take measures that allieveate this phenomonon. As Ar_t has made clear, he currently manufactures digital amps. I seriously doubt he would make and then advertise a product as having a trait that is the most damning in the business. Furthermore he has opined that this particular tratit in this particular technology seems to be more system dependent than usual. I don't have the experience as to whether digital amps have become the new standard bearer presently or if they will in the future. I am hopefull that they will. At the very least they show great promise.