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Do tube amps REALLY clip more gently than solid state?

DanielT

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Have you raised this? Tube amp as well as transistor-based can be class A or class AB based constructions. The single end, the black tube amp I showed is a class A design. All tube amp single end are class A based amplifiers.

Push – pull amplifiers use two nominally identical gain devices in tandem. One consequence of this is that all even-order harmonic products cancel, allowing only odd-order distortion. [11] This is because a push – pull amplifier has a symmetric (odd symmetry) transfer characteristic. Power amplifiers are of the push-pull type to avoid the inefficiency of Class A amplifiers. [Citation needed]

A single-ended amplifier will generally produce even as well as odd harmonics. [12] [13] [14] A particularly famous research on "tube sound" compared a selection of single-ended tube microphone preamplifiers to a selection of push-pull transistorized microphone preamplifiers. [15] The difference in harmonic patterns of these two topologies has henceforth been often incorrectly attributed as difference of tube and solid-state devices (or even the amplifier class). Push – pull tube amplifiers can be run in class A (rarely), AB, or B. Also, a class-B amplifier may have crossover distortion that will be typically high order and thus sonically very undesirable indeed. [16]

Class-A amplifiers measure best at low power. Class-AB and B amplifiers measure best just below max rated power.[citation needed]

Soft clipping
is a very important aspect of tube sound especially for guitar amplifiers. A hi-fi amplifier should not normally ever be driven into clipping. The harmonics added to the signal are of lower energy with soft clipping than
hard clipping. However, soft clipping is not exclusive to tubes. It can be simulated in transistor circuits (below the point that real hard clipping would occur). (See "Intentional Distortion" section.)

Large amounts of global negative feedback are not available in tube circuits, due to phase shift in the output transformer, and lack of sufficient gain without large numbers of tubes. With lower feedback, distortion is higher and predominantly of low order. The onset of clipping is also gradual. Large amounts of feedback, allowed by transformerless circuits with many active devices, leads to numerically lower distortion but with more high harmonics, and harder transition to clipping. As input increases, the feedback uses the extra gain to ensure that the output follows it accurately until the amplifier has no more gain to give and the output saturates.



Took some screenshots, mostly to show that it can be found online (plus a little from Wikipedia).Please do not ask me to explain what Douglas Self
show. Too advanced for me but in any case for those who are interested.:D

Edit:
As for the tube amp. At the aforementioned Vintage DIY fair, I happened to hear two tube amp DIY people talk about the plans for their coming project. One of them asked (the first thing he asked): Found some sensible, good so far?

What he asked you can think about. Those of you who work with tubis know exactly what it's about.:)
 

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tvrgeek

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I can tune a transistor amp input stage and balance between IPS and VAS with global feedback to favor even or odd order harmonics.
It is not as simple as SE or P-P.
Performance of class A or class B is more to do with the implementation than technology. I have heard some terrible class A. And some good ones too. There are some very good methods of reducing crossover to virtually approach class B with AB performance. I can also crank up the bias in an AB to keep it in A most of the time. Does not matter. I get better changes with the input and voltage stages.
 

DanielT

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Performance of class A or class B is more to do with the implementation than technology.
Absolutely but no matter how you twist and turn it, without good output transformers it will not be good.
(in addition to everything else that should be good with the construction/implementation but they, output transformers, are the expensive
things when it comes to tube amps).
 

rdenney

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The classic check-mark distortion-vs.-power curve doesn't distinguish different kinds of distortion, perhaps. This is just arm-waving, but I wonder if the soft-clipping circuits really just clamp down on high frequencies when clipping is detected? This would take the resulting square-wave shape and roll the edge. I think to have an audible effect, the rolloff would have to clamp down to the "crispy-fried" sound range, maybe the upper four digits or lower five digits Hz. The sound would become more dull, but the worst of clip-induced high harmonics would be constrained. That, coupled with a compressor that dials back all output when clipping is detected. I'm just not sure that would look any less like distortion on that distortion-power curve than hard square-wave clipped waveforms would.

McIntosh intentionally designed a soft-clipping circuit into their amps for years, and maybe still do.

Rick "arm-waving" Denney
 

DanielT

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The classic check-mark distortion-vs.-power curve doesn't distinguish different kinds of distortion, perhaps. This is just arm-waving, but I wonder if the soft-clipping circuits really just clamp down on high frequencies when clipping is detected? This would take the resulting square-wave shape and roll the edge. I think to have an audible effect, the rolloff would have to clamp down to the "crispy-fried" sound range, maybe the upper four digits or lower five digits Hz. The sound would become more dull, but the worst of clip-induced high harmonics would be constrained. That, coupled with a compressor that dials back all output when clipping is detected. I'm just not sure that would look any less like distortion on that distortion-power curve than hard square-wave clipped waveforms would.

McIntosh intentionally designed a soft-clipping circuit into their amps for years, and maybe still do.

Rick "arm-waving" Denney
Soft clipping. In the same breath, the world's best-selling amplifier must still be mentioned, NAD3020.


Edit:
Soft clipping is in many ways associated with NAD. Here is another:

 

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RobL

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McIntosh intentionally designed a soft-clipping circuit into their amps for years, and maybe still do.

Rick "arm-waving" Denney
The “Power Guard” would get tripped regularly on my old MC2125, usually by visitors on New Years Eve and such…you’d also hear a big moan, always seemed to come on too easily. ;)
 

DanielT

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Buying tips when it comes to tube amp. Talk to someone here at ASR who works with tubis. Who can tube amps, who knows which models that make sense. I'm not a tube guy, but I would have done that anyway.:)

There are good and bad Hifi stuff from China so do not pull all tube amp from China over one comb, so to speak.

Of course, there is good and bad Hifi in all countries. Do not think that well known people in themselves who have designed and market a tube amp is a guarantee that it is good, see::(


Or, see attached image the same mentioned thread, # 753

The output transformers are the key to any good tube amp. Without a good OPT nothing else really matters.


Choose recognized, proven brands, models for example::)


Edit:
An SS amp with enough power and inaudible distortion then the problem with clipping is solved (because it is not, or rarely driven into clipping).
Good tube amp costs a lot of money. It is possible to get better sound for less money by choosing an SS. So it's pretty irrational to do tubis. But who said it has to be rational? As long as you have fun and enjoy what you do.:p
 

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