How close to the real thing?

I suspect that Mapman is correct for reasons coming from the other side. I have been surprised how my new Tube guitar amp changes character depending on how long it has been on and such. If I can change the source based on tube temp? than it makes sense that a tube output system may display this as well?

Paulsax, if I don't leave my ss gear on 24/7 it takes at least an hour to sound its best. With the high cost of tubes and electricity, few leave their tube gear on.

Yes, feedback is somewhere in there. But there is correct feedback, and "bad" feedback! If feedback was inherently not good then no piece of recorded music could ever be made to sound good, since every recording device and studio is riddled with feedback design techniques and circuitry, going back to almost the very start of electronic recording.

This is incorrect. The Ampex 351 tape machine, used by both RCA and Mercury (and a host of others) has a zero-feedback recording circuit. Neumann microphones use small tube preamps which are zero feedback. I can go on but you get the point.

there is no way that well-designed solid state amplifiers "tend to have these higher odd orders all the time. This is one of the reasons they tend to sound hard or bright. Now its important to note that these harmonics do not have to be very distorted, usually 100th of a percent are audible, simply because these harmonics are so important to the human ear." Total harmonic distortion, meaning any and all spurious frequencies away from the fundamental, is normally at about -70db or better, usually better, and there's no way that such low-level distortions could possibly cause amps to sound hard and bright.

OK- you obviously understand how low the distortion levels are we are talking about. I think I did express that 100th of a percent is audible- seems like that needs more emphasis. Since we humans use the odd orders (5th, 7th and 9th) in order to determine how loud a sound is, obviously while the ear is not sensitive to *some* things, this is one thing that the ear is *very* sensitive to. BTW all of this has been known since the 60s and Norman Crowhurst was writing about this subject in the 1950s.

So this is indeed a way that explains why transistor amps can sound harsh while having otherwise flat frequency response. Note also that with many transistor amplifiers, as power output decreases there is a dip in distortion and then it rises again as power output continues to decrease. This is one of the reasons that low level detail is challenging for transistor designs.

It also points to the way to make transistors work as well as tubes, FWIW. I can point to several SS amp manufacturers that have been exploring zero feedback designs and some of them are as good as some of the best tube amps I have heard. Mind you this coming from a tube amplifier manufacturer...

This is incorrect. The Ampex 351 tape machine, used by both RCA and Mercury (and a host of others) has a zero-feedback recording circuit. Neumann microphones use small tube preamps which are zero feedback. I can go on but you get the point.

Sorry Atmasphere, but you're mistaken - recording, mastering, and broadcast equipment all does indeed use a variety of "feedback design techniques and circuitry, going back to almost the very start of electronic recording," as Fas42 states. Specifically, the Ampex 350 and 351 used frequency-dependent negative feedback in the cathode circuit of the record output tube, and negative feedback around the playback head amplifier for playback EQ. Additionally, the 351 had a push-pull (12AU7?) transformer-coupled line-output amp with a separate feedback winding for global NFB, very similar to a little transformer-coupled power amp.

And then there's the record cutting lathe - virtually all high-fidelity cutting heads use negative feedback from a separate winding to provide global negative feedback from the motion of the cutterhead back to the cutting amplifier.

Do Ayre and Pass use zero feedback desings in their amps? I only know they sound really good.