Class ABCD ?

[E-Stat]

Why battle anyone , shouting on an internet board does not make anybody right

Guys, guys (and I'm including RGA) waddya say we tone it down a notch? We don't need to use "mad" emoticons here, ok?

rw

[theaudiohobby]

Perhaps you should tell this to Bryston!

I think most amplifiers nowadays are Class AB.

Some have raised the question of distortion. While it is true that low distortion measurements tell us nothing about the sound, the comparison of tubes and solid state on this basis is often useless, as distortion is usually below audibility.

The biggest difference in sound between solid state amps and tube amps lies in the output impedance....

I think the real key to the difference is thermal noise, as Ken Ishiwata said a while back (not an exact paraphrase) , "It is their noise that makes them suitable for audiophile applications, if you design well, this noise will give a 3D atmoshphere that transistors can never have"

[GMichael]

I think the real key to the difference is thermal noise, as Ken Ishiwata said a while back (not an exact paraphrase) , "It is their noise that makes them suitable for audiophile applications, if you design well, this noise will give a 3D atmoshphere that transistors can never have"

Is there a way to find out what the thermal noise is for a given model?

[RGA]

the audiohobby only posts to me to make an argument that I never made -- you want to be corrected on your article go to the AA thread and argue against the rebuttle there. There is zero in that article that mentions anything directly against what AN posted and there is zero rebuttle from you in mathematics to the pnts raised in the AA thread. Take it there because it is off topic here.

You merely go after everyone on every forum you visit. You never make any real technical arguments with any sort of real evidence just post links which almost but doesn;t directly make a case against what is being discussed. Sort of luike an ex=poster here named Mrtycrft who would post a DBT of amplifier s inn 1980 when the topic is about cables. there is no conclusive evidnce in that aticle as AA posters have already said -- you choose deliberately to avoid those poster's comments and try and weasal out of it here.

I will hear your tilted up cold unengaguing treble that the reviewers mention next year. LOL even you had to get new speakers I see -- But the 705 is useless and so your ear says it all to me.

[theaudiohobby]

Is there a way to find out what the thermal noise is for a given model?

For a given model, Yes but not easily, the thermal noise generated by the tubes utilised can be calculated and an extrapolation can made for a given model provided the amplifier's operating conditions are known.

[GMichael]

For a given model, Yes but not easily, the thermal noise generated by the tubes utilised can be calculated and an extrapolation can made for a given model provided the amplifier's operating conditions are known.

But a little more involved than what I am ready for. I guess I'll have to settle for listening.

Thanks

[theaudiohobby]

But a little more involved than what I am ready for. I guess I'll have to settle for listening.

Thanks

Excellent idea, especially since the noise itself is part of the alluring features of the amplifiers , after calculating the noise contribution how do you directly correlate it to your listening experience? Just listen and buy what you like.

[theaudiohobby]

Triodes have degeneration, not feedback. They ain;t the same --- sorry but you have no clue.

I will be remiss if I do not post these comments made by the poster that you originally quoted, in one of his responses to me, he said this

No-one is disputing that cathode degeneration is NFB.

So back to the original question, Do triodes (including triode amplifiers) have negative feedback? Yes Indeed, they do.

[RGA]

And your point was 1. The original supposition was that a grounded cathode triode amplifier is fully equivalent to a pentode with NFB due to the inherent NFB action of the plate resistance. This is false.

BTW from the exact same poster you quote "Triodes have degeneration, not feedback.
Yes there is a difference." Feedback involves feeding back some of the output signal to the input, which means that the signal presented to the input is different from the open loop case.

Degeneration means that the output affects the field within the triode in such a way that the output is different from the "open loop" case with the same input."

BTW since you obviously only posted this to attack Audio Note -- just so you know they don;t claim all their amps are no negative feedback. Mine for example uses some negative feedback as does the Soro. The Meishu is zero negative feedback.

To prove you are right to me -- take them to court for false advertising. Yeah thought so!

[theaudiohobby]

And your point was 1. The original supposition was that a grounded cathode triode amplifier is fully equivalent to a pentode with NFB due to the inherent NFB action of the plate resistance. This is false.

BTW from the exact same poster you quote "Triodes have degeneration, not feedback.
Yes there is a difference." Feedback involves feeding back some of the output signal to the input, which means that the signal presented to the input is different from the open loop case.

Degeneration means that the output affects the field within the triode in such a way that the output is different from the "open loop" case with the same input."

BTW since you obviously only posted this to attack Audio Note -- just so you know they don;t claim all their amps are no negative feedback. Mine for example uses some negative feedback as does the Soro. The Meishu is zero negative feedback.

To prove you are right to me -- take them to court for false advertising. Yeah thought so!

Obfuscation does you no good, here is my original post on the subject.

Good marketing spill but like most other ad-copy's it is factually wrong, not the least because the much vaunted triodes use negative feedback to linearize their output just like any other amplifying device be it tetrodes, pentodes or transistors.

When all is said and done, it still comes down to this, a triode uses negative feedback, type of feedback is besides the point, to linearize its output. It is no different from any other semiconductor in that respect, afterall it is semiconductor, another piece of misinformation from the original blurb. And get over your paranoia, the original post was simply addressing marketing misinformation.

[RGA]

I think people here can judge for themselves by reading that thread. You kept changing the premise to get him to agree with you -- that is Obfuscation.

Agian take them to court for false advertising -- then we will all see who is proven wrong.

Their more complete argument is made here http://www.audionote.co.uk/anp2.htm

Martin Colloms:

"At this point the proceedings took on an educational dimension, as the big Cary offers the fascinating feature of user-adjustable variable negative feedback. In fact, the degree of negative feedback can be reduced right down to zero"

Without feedback, both I and my friends and colleagues who shared the listening found that reproduced sound could really be different from the usual expectation, that a pervasive grayness of expression and false tonal color had been swept away without dire consequences for other important aspects of sound quality.

I can hear the arguments already: "This amplifier is probably so wrong that it can't use feedback successfully...it's one of those rare cases where negative feedback makes it worse."

Somehow I don't think so. An analysis of the approximately 700 amplifier reviews that I've undertaken over the years indicates that, if there has been any trend associated with improving sound quality, it has largely been associated with reductions in global negative feedback. Even the majors---Mark Levinson, Krell, Audio Research, Conrad-Johnson---have consistently moved toward more elegant, more linear circuitry, allowing lowered feedback levels for the same closed-loop linearity. Are these designers unconsciously and instinctively seeking a safe route toward designs with minimal or no negative feedback?

Let's consider the outrageous proposition that corrective feedback is fundamentally unmusical. In my reviews, I have observed that high-feedback amplifiers---which have an inherently limited open-loop bandwidth---suffer what is commonly called "midrange glare": a hardening of and forwardness in the upper midrange. Amplifiers with wider open-loop bandwidths have less of this, or their "projection" moves up to the mid-treble. Low-bandwidth, high-feedback designs can end up sounding "dark," even significantly colored in the midrange.

A typical amplifier with feedback disconnected may have 20% of complex distortion. Closing its negative feedback loop---60dB of feedback is not unusual---will reduce the level of that distortion to a level suitable for the printed specification, but perhaps not for sound quality. Investigation has suggested that the open-loop break frequency is involved---the point at which, without any negative feedback, an amplifier will filter out the upper frequencies (fig.3, top trace). Without feedback, the open-loop break frequency could be as low as a few hundred Hz; these days it is typically 500Hz to 1kHz, and may be as high as 5kHz in wide-band designs. Normally you can't see this low-pass "filter," as it's buried by negative feedback: with its feedback loop closed, the amplifier may have a measured bandwidth 100 times greater (fig.3, bottom trace). Yet I reckon that the buried filter comes back to haunt us in the form of "glare"---a coloration centered around the amplifier's intrinsic open-loop, low-pass function, perhaps due to the nonlinearity of feedback itself.

Consider the proposition that a pure input signal is subjected to the usual nonlinear amplification and is then applied with all the subsequent errors back to the input to be amplified again. In theory, the errors are subtracted at the feedback connection, but there is inevitably some error in this subtraction. No problem, says the textbook: the wide bandwidth of the closed-loop amplifier will ensure that the signal and errors, and their errors, will go many times 'round the loop, reducing the distortion to below audible levels.
Or will it? Audiophile pundits know only too well that making a single audio stage perform to a truly high standard is not a trivial matter. Almost by inspection you can see that the feedback amplifier has the capacity to go on compounding its error residual. When an amplifier is processing a complex, harmonically rich input signal---music---and not a steady-state single sinewave tone in a lab test, something could well go wrong. That cascade of residual errors will intermodulate at low levels, but it will intermodulate in a fantastically complex manner.

Subjectively, the effect of increased negative feedback is generally that of increased compression, in addition to the midrange coloration noted above. This loss of dynamic expression suggests that additional energy is indeed filling in the natural spaces in the original spectrum and thus blurring musical expression.

A Future Without Feedback?
When Black proposed negative feedback in 1927, he was trying to solve a specific problem: the deep cascading of imperfect, transformer-coupled tube amplifiers. But has anyone explored the implications of negative feedback for reproduced sound quality in the absolute sense?

Based on my experience of the pairing of a zero-loop-feedback preamplifier and amplifier, and supported by the evidence that amplifier designers consciously or unconsciously attempt to reduce negative feedback to improve subjective quality---even if this means worsening the measured performance---we need to reconsider the subject.

It is possible that engineers need to rethink how audio systems should be designed. Before the introduction of transistors limited to low voltages, which forced the speaker industry down to 8 and 4 ohm impedances, speakers were typically 8 to 16 ohms, did not need thick cable to wire them up, achieved maximum electromagnetic utilization at good efficiency, and were well matched to tube amplifiers. Higher efficiency spells better dynamics, reduced thermal compression, and the potential of using smaller, more perfect power amplification. But if speakers were designed to have smooth impedance curves, to be relatively uncritical of amplifier or cable matching, and to offer higher sensitivity, we would have greater freedom to examine the feedback question and the validity of the low-power, short-path, zero-feedback approach.

We still have much to learn about the art of sound reproduction; ultimately, our responsibility is to our ears, not to established precepts.

by Martin Colloms B.Sc. (Hons), C.Eng, M.I.E.E
Audio Writer and Electroacoustics Engineer,Patents, Expert Witness

Technical Advisor and Contributor, Hi Fi News and Record Review, London
Senior Contributing Editor, Stereophile Magazine, New York, NY

[theaudiohobby]

What does this have to do with the fact that all amplifiers use negative feedback (in whatever form) to linearize their output. . Degeneration is a form of NFB and it is not unique to triodes, without NFB the triode circuit will go into oscillation, you cannot avoid it, wet and water go together!

[RGA]

Seems like everyone uses the words "no negative feedback" Even mark has already stated that degeneration is NOT the same. Seems odd you use him as a source to make one point and then ignore the other point.

You are basically saying martin colloms and everyone who uses the words no negative feedack don't know what they;re talking about because you cited one source of non peer reviewed support and then weasal out of it and around it.

Prove to us all that the Meishu uses Negative Feedback and don;t give us this lame it's inherent in the tube because that is not the same thing as Negative Feedback used by say Bryston

[theaudiohobby]

Seems like everyone uses the words "no negative feedback" Even mark has already stated that degeneration is NOT the same. Seems odd you use him as a source to make one point and then ignore the other point.

You are basically saying martin colloms and everyone who uses the words no negative feedack don't know what they;re talking about because you cited one source of non peer reviewed support and then weasal out of it and around it.

Prove to us all that the Meishu uses Negative Feedback and don;t give us this lame it's inherent in the tube because that is not the same thing as Negative Feedback used by say Bryston

Whilst Martin Colloms is respected in audio circles, neither he nor Mark Kelly nor person you care to name has published any peer-reviewed paper refuting Stockmans basic conclusion, Mark Kelly quibbles with the model, but that is just it quibbling, Stockman pointed out many moons ago and is now widely accepted (see the previous link) that Degeneration is a form of NFB and it is intrinsic to the operation of triodes. And Tube circuit designs that are publicly available for critical assessment concur with Stockman's conclusion. Many publications (including some manufacturers) that discuss tube circuits on the web treat inherent NFB and degeneration as synonymous terms with some providing the mathematical background for this treatment.

Cathode degeneration is NFB and cathode degeneration is intrinsic to the operation of triodes, it follows then that NFB is intrinsic to a triode's operation, to say otherwise is to have a play on words. And as Delétraz pointed out, you can avoid global feedback completely, but you cannot completely avoid intrinsic and local feedback in amplification circuits.

Stockman has already provided proof and that proof has stood the test of time. Since the Meishu cannot operate outside of the boundaries of a triode's (in this case a 300B) limitations, the circuit uses some NFB despite of what the manufacturer ads say. Granted it may not utilize global negative feedback but then again that approach is not unique to triodes. In the context of this discussion, your question about the Meishu and Bryston is non-sequiter as are some of your other comments in the cause of this discussion.

[RGA]