[Phil]

Eeyore wrote:

Phil wrote:


Phil Allison wrote:

"Phil"
Andre Jute wrote:

We're
not talking about "-30 degrees at 20 KHz," we're talking *dynamic* phase
shifting, the kind that makes a Crown preamp bite your ears off, while
testing at 0.0001% THD.

Let's hear some more about this dynamic phase shift that pours a pint
of vinegar into a Crown preamp. I'm not overimpressed with vanishign
THD but this is an amazing explanation for why so many silicon amps,
and not a few tube amps, sound like ****.

Pretty much what Patrick said, although I need to reply in the original
thread. What Matti Otala PROVED --


** Otala never proved one, single commercial hi-fi amp suffered from TIM in
a way that was audible.

Many others have proved conclusively that TIM ( ad his cousin SID) is a
furphy.

Could you name an article showing that slewing induced distortions do
not exist? I can use an op-amp with 1 V per millisecond maximum slew
rate with no problems with signals at 10 V per millisecond?


Eh ?



Surely
someone as intelligent as yourself (although it pains me to admit it)
wouldn't use that old, tired, debating trick of throwing out a "general
criticism without any supporting examples."


Firstly your slew rate figures are surely V/us ( microsecond )

No, I'm making a point that, contrary to what Phil said, slew induced
distortion can indeed be a problem.

For any sinewave ( see Fourier theory for applicability ) the max slew rate ( at
zero crossing btw ) is 2.pi.f.Vpeak.

For a 20kHz signal of say 2V peak amplitude that means a slew rate of 0.25 V/us
! Even a rubbish 741 or 1458 can manage that !

Given that modern audio op-amps are capable of slew rates of ~ 10V/us - you're
never even remotely close to slew limited anything.

Graham

Well, remember, the maximum slew rate found in audio signals is much
greater than what a theoretical 20 KHz signal is going to supply, and
not all power amps, with their big, slow, output transistors, are going
to be as fast as even a 741. Plus, the point of Matti's work is that
problems begin to appear at all levels below the theoretical
"breakthrough" point of TIM/SID. In any case, the topic here is not
whether most amps have sufficient slew rate -- I assume that *most* good
amps do -- but rather about Otala's proof that a feedback amp's
"correction" of an amplitude distortion of the open loop phase shifts
the high frequency components in the closed loop. I am currently
discussing this in the "Negative Feedback in Triodes: The Logical and
Experimental Proof" thread from 8/15, so if you're interested, look
there (articles posted on 9/6). Phil Allison had a "response" here --
his usual slams and blams with no supporting evidence -- but I actually
would like to see his simple test that can show whether low frequency
signals in a feedback amp do or do not cause high frequency phase
shifting, as it would be useful test, and I'm having a hard time coming
up with a simple way to test that myself. Apparently, Otala incorporated
a lot of ideas/solutions into his Citation XX power amp, and maybe, if I
can find papers by him on that amp, there will be some useful
information and tests there, but if PA can come up with something in the
meantime, hell that's fine by me! He'll probably think of something
really simple and easy, and then refuse to tell me, the ****head ...

Anyway, what PA was saying/yelling is that feedback amps DO NOT EITHER
CAUSE PHASE SHIFTING OF THE HIGH FREQUENCIES LIKE THAT DUMMY DR. OTALA
SAID! My response was simply to ask whether (1) he knew of references
that would back up his claim, that Otala's analysis was flawed, and (2)
whether he knew of a good, simple test that can be used to test whether
LF signals in a feedback amp cause phase shifting of the HF signals,
like Otala said they do.

Phil

To email me directly, cut off my head