How close to the real thing?

I am a VERY new member to the BAS and I am NOT speaking for them at all! I simply asked a couple of their members the same question that is being posed here for their opinion just as I asked my musician friend for his opinion.

Happy New Year Irv!

Ed

Fas42, on that page you will see a pattern diagram. I pointed this out as it is an example of a strange attractor.

Now what Chaos Theory has to say about this confirms what Crowhurst has pointed out in various places in his writings:

By the use of feedback in an amplifier there will be a harmonic noise floor (bifurcation) injected into the output of the amplifier. The amplifier will thus exhibit stable and chaotic behaviors.

The harmonic noise floor is inherently different from that of a noise floor composed of hiss. Our ears can hear about 20 db into the latter but none into the former. So the effect in an amplifier with loop feedback is that low level detail will be truncated and this is readily audible (IME) as a loss of ambient and soundstage information.

So its my opinion that you want the amplifier to behave in a way to more closely adhere to the rules of human hearing. I am adamant that the rules of human hearing trump all other considerations. In this case the masking rule of human hearing is where the problem is: we can't hear into that harmonic noise floor. Ridding the amplifier of negative feedback takes care of this and also rids you of the problem of making the slight amount of odd-ordered distortion that is part of that noise floor.

So you kill two birds with one stone, but you introduce another problem- how to get rid of lower-ordered harmonic distortion, which can also mask detail. The ear will hear this as a warmth, bloom or fatness in the lower registers and some people do find it annoying because the coloration can be obvious. BTW, this is something tubes are very prone to.

So IMO/IME, you have to do everything you can do eliminate distortion without feedback. That can be a bit of a trick and there is no one single design panacea for that.

Atmasphere,

I am adamant that the rules of human hearing trump all other considerations

Agree 100%.

So the effect in an amplifier with loop feedback is that low level detail will be truncated and this is readily audible (IME) as a loss of ambient and soundstage information

Unfortunately, disagree 100%. IF the feedback is done badly or is extremely minimal in its effect then that may be the result. I agree that "low level detail is truncated" is often the way distortion manifests, but my experience is that this is lousy power supplies and a myriad of other subtle mechanisms causing problems, which insufficient feedback may struggle to compensate for, but only ends up making things worse. In other words, the overall engineering of EVERYTHING has to be got right, and then that "harmonic noise floor" you speak of will be reduced to a level well below audibility

Frank

Look at a concert. Any concert. Chances are they have horn tweeters and midrange speakers and a big woofer in a speaker array. You get NO IMAGING. Stereo is a imaging experience that make one think he is in a studio not a hall,if you want a loud wall of sound get horn speakers. If you want the studio sound get non horn.

Vernneal, consider that at a concert imaging in the PA is not important. You may well be listening to mono.

Horns have no trouble doing imaging, that's for sure. There are other threads that have covered this subject.

Fas42, I agree completely about the power supplies. In fact I run a separate power supply with its own power transformer for the driver section of our amplifiers. The idea is to prevent any sort of noise that might occur in the output section from having any influence on the driver. This is one of the ways to really reduce IM distortion, as the power supply noise issues are usually modulation issues, but the effect is less pronounced for THD.

And I also agree that the engineering has to be right- you are absolutely correct that there are a ton of variables that affect any design and its easy for a problem in just one of those variables to completely overshadow other design parameters. IMO right here is where you encounter the human element in design.

Y'all have a nice holiday!!