Solid-State vs Tube Amps: The "science" behind the difference? - AVS Forum
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post #1 of 82 Old 07-08-2009, 11:33 AM - Thread Starter
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On his site http://www.high-endaudio.com/RECENT.html#June, Arthur Salvatore gives a "scientific" explanation of the differences between solid-state and tube amplification. I have read the passage several times, and I'm still looking for his explanation.

Here is an abridged version. He is discussing a Titan amplifier (emphasis mine):

____________________________________________________________ _____

"I can state this with near certainty, because even though I've never heard the Titan, it is a fact that no transistor amplifier, using current technology, and with that much power (and thus with unavoidable "size" and ultra-complexity), can equal any good tube amplifier in their unique sonic strengths, and especially the finest single-ended-triode (SET) models (with their highly contrasting ultra-short signal paths and their ultra-simple circuitry). There's a scientific reason for this.


The laws of physics, on a micro-level, have always precluded this "bridging the gap" from happening, and ignoring those laws, along with hoping and wishing, and/or spending huge amounts of money, won't change that unfortunate reality. If this weren't so, tube amplifiers for the home would have disappeared 40 years ago. Instead, despite their greater cost and impracticality, tube amps are still popular with the most serious audiophiles and/or music lovers , and this will continue until there is a true technological breakthrough in transistors or humans experience an evolutionary and collective hearing loss (of ultra-soft sounds)."

____________________________________________________________ ____

Can anyone help me (or him) with the science? He never discusses the "scientific reason". What is the theory at work? (i.e. theory as an analytical framework to explain empirical observations)

Or this just more audiophile b.s.?
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post #2 of 82 Old 07-08-2009, 12:09 PM
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Ultra short signal path. Yeah, those electrons hate going round and round.

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post #3 of 82 Old 07-08-2009, 12:30 PM
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Um, haven't you answered your own question? There is no science there, as you rightly note.

Tube and SS amps have different distortion profiles—and tubes tend to have a lot more distortion, period. Some tube amps are clean/powerful enough that they are audibly indistinguishable from (similarly powered) SS amps. Others are not. That's the difference.

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post #4 of 82 Old 07-08-2009, 12:50 PM
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Ok, lets first take a look into tubes and transistors:
1.) Tubes work mostly in a vacuum (though some special tubes do not) and use the principle of electron attraction from the overcharged cathode to the receptor anode by thermionic emission. This allows them to act as a diode and with some other alteration a switch. The switch works on the principle of electrons being able to flow through a vacuum. With a grid added to the tube, one can add voltage to the grid to control the flow of electrons between the two electrodes (in its most basic design).
2.) Solid State Transistors use two types of silicon derived from doping of different gases. P and N type silicon, in the most common designs. One type sits between the other, when a small voltage is applied, because of the special doping, it then allows electricity to flow through it, any other time it does not. Thus it acts as a switch.

Techinically speaking, both switch at extremely fast rates, enough to not be noticable for things like audio. Harmonic distortions are created in both, which is where the main difference lays.
Although i have no source on this, i've heard tubes produce even integer harmonics, where solid state amps produce odd integer. If this is true, this it follows that the harmonic distortion from a tube amp will sound better than that of a solid state amp. This is because square waves (as opposed to most audio which is sinusoidal) are produced by odd integer harmonics, thus solid state amps are bound to produce square wave sounding distortion.
However, all this means is that a cheaply made tube amp probably will sound better than a cheaply made solid state amp... but these days even the low end is very well made, so i doubt there will be much of a difference.
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post #5 of 82 Old 07-08-2009, 12:51 PM
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Well, if you read the website, the guy is a tube lover. It's his thing. Like some people are chubby chasers, some like Mustangs, etc.

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post #6 of 82 Old 07-08-2009, 12:57 PM
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Although i have no source on this, i've heard tubes produce even integer harmonics, where solid state amps produce odd integer.

I've got no immediately linkable source for this, but my understanding is that tube amps often have more of both even and odd order HD. I' can't recall ever seeing measurements of a modern SS amp that shows audible levels of odd-order HD.

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post #7 of 82 Old 07-08-2009, 12:57 PM
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Originally Posted by Chu Gai View Post

Well, if you read the website, the guy is a tube lover. It's his thing. Like some people are chubby chasers, some like Mustangs, etc.

Chubby chasers?
That label might apply to tube heads!
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post #8 of 82 Old 07-08-2009, 01:01 PM
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Originally Posted by mcnarus View Post

I've got no immediately linkable source for this, but my understanding is that tube amps often have more of both even and odd order HD. I' can't recall ever seeing measurements of a modern SS amp that shows audible levels of odd-order HD.

Yeah, as i said, i have no source on that info, its only what i've heard. But, if i have some free time tonight (doubtful though) i'll hookup my scope to my sub amp (its cheap and produces quite a bit of harmonics) and see.
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post #9 of 82 Old 07-08-2009, 01:40 PM
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Ah, more trite "tubes produce these and transistors produce those" stuff.

I've used transistors to produce even-order and odd-order harmonics alike. And a couple times I've used tubes to do it.

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post #10 of 82 Old 07-08-2009, 01:41 PM
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Does Arthur Salvatore actually have a scientific reason, or does he just allude to there being one?

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post #11 of 82 Old 07-08-2009, 02:03 PM
 
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Techinically speaking, both switch at extremely fast rates, enough to not be noticable for things like audio.

Tubes and transistors are biased to operate in a linear fashion when used as amplifiers.
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post #12 of 82 Old 07-08-2009, 02:10 PM - Thread Starter
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Quote:
Originally Posted by Bob Lee (QSC) View Post

Does Arthur Salvatore actually have a scientific reason, or does he just allude to there being one?

When I started this thread, I presumed he either had no scientific reason, or he assumes we would all nod our heads in agreement.

He states that the laws of physics are operating on a micro level

As far as I know, all his communication is one-way only. He does not participate in online forums, which neatly avoids the problem of being confronted with responses to his pronouncements on all things audio.
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post #13 of 82 Old 07-08-2009, 02:33 PM
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He's also got a crappy website design.

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post #14 of 82 Old 07-08-2009, 02:38 PM
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In addition to the likelihood of higher distortion (if potentially but not necessarily more pleasant distortion) tube amps are more likely, as I understand it, to have a high output impedance, so their frequency response will vary to a greater extent than any normal transistor amp depending on impedance profile of the speaker they are connected to. That's surely an overbroad statement, but generally true. Se even operated so that their distortion is below audible levels, typical tube amps may sound different from typical transistor amps. Most obviously by rolling off in the bass.

This from a guy who LIKES tubes in stereo gear (and insists on them in guitar amps). FWIW, while I like 'em, I own no tube home audio devices.

BTW I was looking at info on a semi new design by one of the botique guitar makers, and whoever was talking suggested that 6L6 tubes' distortion has more even-order harmonics than EL-34 tubes. I've seen similar statements before but have no idea if they are true. And of course, in guitar land, we are intentionally pushing our power tubes into distortion because it sounds good for certain applications,so how the device distorts is perhaps more important, since we know we will be pushing it into audible distortion. It is hard, in my estimation, to really know to what extent the overall sound of a device is dependent on the specific output tube versus other areas of the design. Generally 6L6 amps sound different to me than EL34 amps, but I've heard 2 EL 34 amps that sound just as different from each other. There are some boutique-y designs that let you roll in those different output tubes, but the ones I've gotten to fool with sound like cr@p to me. I don't care if it sounds a different kind of bad if I change the tubes, and never had the patience to play around with them much.
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tube amps are more likely, as I understand it, to have a high output impedance,

Hence the use of impedance matching transformers on the outputs.
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post #16 of 82 Old 07-08-2009, 03:06 PM
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Oh man, a lot of Torontonian audiophiles (like me) have Arthur Salvatore stories. Classic
crazed/passionate audiophile he is.

I love tube amps (some of them at least). I understand their yummy distortion can come from various places, but a lot of people point their finger at the output transformers.

I recently bought a classic EICO HF-81 tube integrated amp (circa 50s/60s). A sought after gem for tube amp aficionados. It sounds gorgeous in that classic tube-amp way.
Some say it's a combination of the design and especially the output transformers uniquely made by EICO for that period.

I don't know what it is, but it's damn fun to put in the system. Stereophile did a rave about this amp a few years ago which, of course, means you have to pay more for one now if you find it vs before the Stereophile review.

I actually read the Stereophile review after hearing the Eico. I didn't even want to look at the review's "Measurements" section for that amp. It was sure to be bad news And I didn't want to start hearing those measurements, if'n ya know what I mean. As it is I can just enjoy using the amp for what it does for my listening experience...whatever the reasons.
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post #17 of 82 Old 07-08-2009, 03:20 PM
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I highly recommend reading David Manley's book on tubes. (VTL).

Circuit implementation has more to do with it than the actual component. You can make a good or bad amp with either. You can make almost any "overly sweet" tub amp sound much like a bi-polar with only the addition of small grid isolation resistors. I did this in an old Knight 30W amp. You can make a MOSFET amp generate 20% second order harmonics, just like a tube. Did that too to a Sanyo Plus.

It is all about the transfer function. Like Hafler showed, "Is the output exactly the same as the input, just bigger?"

Further argue, Carver built the best tube amp he could as a benchmark to show his best solid state amp sounded just the same. It did, but the tube lovers bought the tube amp anyway. He made money, what the heck.

If the unit does anything other than amplify, it is not just an amp, it is a distortion generator. Some may like it, some may not. Personal preference is just that, personal.
"Better" is preference. Accuracy is objective and can be measured. The physics are not a mystery, they are well understood.
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post #18 of 82 Old 07-08-2009, 03:41 PM
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The thing is that I like about whatever tube amps are doing (distortion-wise) is they act as a sort of "fix" for the overly electronic, mechanical sound I get in most systems and from a preponderance of recordings. There are so many little issues in the chain of recording, starting with microphone colorations on down the line to the play back system (how well distortion is controlled at the speaker end, how well integrated the crossover/drivers/overall sound is etc) that add up to an unnatural "squeezed" electronic/mechanical presentation of voices and instruments. Sibilance in voices is a particular giveaway - it often as a too-sharp, electronic "detached from the person" quality compared to real life. What also tends to be missing - almost always - from reproduced sound is the organic quality, particularly the sense of softness of real life instruments. Just today I was listening to a guy playing a nylon-string guitar and occasionally singing (while I was buying an acoustic guitar). I closed my eyes and noted, as I always do, the fatness of the sound, the "fleshy" quality of his fingers on the strings, the organic quality of his voice. That "woody" sound of the guitar.

In comparison, most reproductions of a singers and instruments sound squeezed and harder than life. As if made out of different materials than they really are.

Somehow certain tube amps fill out and perhaps "smudge" the sound, sometimes soften it a bit too, not overtly to make the sound bad or like mud, but just enough and just in the right direction to make voices and instruments - all the frequencies creating them - sound more coherent and organic. Sibilance tends to sit into the mouth of the singer more believably. And the slightly softer, fuller sound at least mimics some of that organic quality I hear in real life. Which is why I find I can sit in front of my system when certain tube amps are in the chain (in my case, tube amps and tube pre-amps) much more engrossed and at ease than when powered by solid state amplification.

But as some here have pointed out, if you know what you are doing it's apparently possible to get a tube amp sounding like a solid state amp, and visa versa.

But that is personal preference. When it comes to the sonic differences between tube and solid state (here talking about those designs that DO sound different) other people find that solid state edges closer to the things they value - what they hear as neutrality, or more realistic transients, tighter bass or what have you. All the distortions that accrue in recording and sound reproduction means the "perfect sound reproduction" is rarely encountered (if it exists). So we tend to concentrate on the things that we, as individuals, find most important to our enjoyment of the sound and the hobby.

While it may be possible to have a solid state amp tweaked to sound like a tube amp, I prefer to have a "real" tube amp because there is also some aesthetic pleasure added
knowing it is "real" tubes doing the work, as well as the warm fuzzies I get from the visual design of some tube amps, seeing the tubes "glow" etc.
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post #19 of 82 Old 07-08-2009, 04:00 PM
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Quote:
Originally Posted by R Harkness View Post

The thing is that I like about whatever tube amps are doing (distortion-wise) is they act as a sort of "fix" for the overly electronic, mechanical sound I get in most systems and from a preponderance of recordings. There are so many little issues in the chain of recording, starting with microphone colorations on down the line to the play back system (how well distortion is controlled at the speaker end, how well integrated the crossover/drivers/overall sound is etc) that add up to an unnatural "squeezed" electronic/mechanical presentation of voices and instruments. Sibilance in voices is a particular giveaway - it often as a too-sharp, electronic "detached from the person" quality compared to real life. What also tends to be missing - almost always - from reproduced sound is the organic quality, particularly the sense of softness of real life instruments. Just today I was listening to a guy playing a nylon-string guitar and occasionally singing (while I was buying an acoustic guitar). I closed my eyes and noted, as I always do, the fatness of the sound, the "fleshy" quality of his fingers on the strings, the organic quality of his voice. That "woody" sound of the guitar.

In comparison, most reproductions of a singers and instruments sound squeezed and harder than life. As if made out of different materials than they really are.

Somehow certain tube amps fill out and perhaps "smudge" the sound, sometimes soften it a bit too, not overtly to make the sound bad or like mud, but just enough and just in the right direction to make voices and instruments - all the frequencies creating them - sound more coherent and organic. Sibilance tends to sit into the mouth of the singer more believably. And the slightly softer, fuller sound at least mimics some of that organic quality I hear in real life. Which is why I find I can sit in front of my system when certain tube amps are in the chain (in my case, tube amps and tube pre-amps) much more engrossed and at ease than when powered by solid state amplification.

But as some here have pointed out, if you know what you are doing it's apparently possible to get a tube amp sounding like a solid state amp, and visa versa.

But that is personal preference. When it comes to the sonic differences between tube and solid state (here talking about those designs that DO sound different) other people find that solid state edges closer to the things they value - what they hear as neutrality, or more realistic transients, tighter bass or what have you. All the distortions that accrue in recording and sound reproduction means the "perfect sound reproduction" is rarely encountered (if it exists). So we tend to concentrate on the things that we, as individuals, find most important to our enjoyment of the sound and the hobby.

While it may be possible to have a solid state amp tweaked to sound like a tube amp, I prefer to have a "real" tube amp because there is also some aesthetic pleasure added
knowing it is "real" tubes doing the work, as well as the warm fuzzies I get from the visual design of some tube amps, seeing the tubes "glow" etc.

Exactly, Distortion. I did not say it was bad, just that it is distortion. Mmmmm, Lynn, Grace, Cary, Quads. Like pouring melted butter all over the music.

Actual science:
Tubes can produce higher voltage gain in one stage, reducing the number of amp stages. Advantage for lower phase or TIM distortion. Poor in current gain though.
Tubes produce predominately even order harmonic distortion. This is less objectionable to the brain than odd order.
FET's behave a lot like tubes and you can use less feedback than a bi-polar to reduce odd order harmonics and still get a "pleasing" sound.
Bi-polar transistors produce predominately odd order distortion requiring higher amounts of negative feedback. Sufficient bandwidth will resolve this limitation.
Tubes kind of just slide through it without being too upset when over driven. Bipolars get ugly when they clip. Fet's just blow up. Much more important when we all had 15W amps.

Where tubes are best used is to solve the original problem. As INSTRUMENTS in the original recordings. To give the artist the sound they want. Then don't mess it up with bad circuit design later. Let's hear it for upside-down Fenders and AKG mics!
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post #20 of 82 Old 07-08-2009, 04:47 PM
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Can anyone help me (or him) with the science?

Sure. Identical transfer functions sound identical. Differences less than thresholds of perception sound identical. That means amplitude response, distortion, and noise.

A single ended triode not driven to clipping doesn't sound any different from a solid state amplifier with the same transfer function, which might be approximated by a resistor in series with the output (this means the speaker has more output where the impedance goes up, like a teenager's graphic equalizer in the classic smiley-face configuration) and perhaps a band-pass filter.

It's better because:
1) You can visualize the electrons flowing from cathode to plate with charges on the grids repelling them. Just look at tube X-rays.

2) Tubes survive the EMP pulse from nuclear detonation.

3) Tubes aren't static sensitive

4) Like real hobbies tubes can kill you with high voltages. It left a mark and got my attention when I put my hand across the grounded chasis on my bench supply and terminal attached to the 450V B+ rectifier.

and MOST important.

5) Tubes have pretty glows. Especially with tube rectification where you can get more than just heater orange and blue from Cherenkov radiation.

Note mesmerizing glow from mercury vapor rectifiers. Pretty!


LL
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post #21 of 82 Old 07-09-2009, 08:21 AM
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Actually, the output transoformer does not eliminate the high output impedance of tube amps. If I had to guess, it adds to it. Just for grins, I went over to the Stereophile page and opened the review of the VTL MB-450, a $13.5K per pair high power monoblock design. (second review under tube power amps - - the first is a class A low power tube amp that has even higher output impedance and a FR swing of something like plus or minus 2.5 dB into simulated speaker load, depending on the transformer tap). Output impedence of the VTL is sufficiently high that into S-phile's dummy speaker load the amp's frequency response fluctuated by "an audible [plus or minus] 1.2 dB." That's the nature of tube amps in general. If you look at the measurements,you'll see the amp is admirably flat into a resistive load well past 20kHz. THD is higher than it might be because of the low NFB design, which is okay with me as long as you know what the tradeoffs are.

Most solid state amps whose reviews I've looked at are more like plus or minus 0.2 dB into the simulated speaker load, because of their much lower output impedances. While a swing that approaxhes 0.5 dB or so over broad regions may be detectable, barely, under some circumstances, there is little question AFAIK that tube amps, much as we may love them, are likely to be less flat into real world speakers than transistors.
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Actually, the output transoformer does not eliminate the high output impedance of tube amps.

No transformer can alter the characteristics of a tube. The transformer is an impedance transformer, it is used to transform the high output impedance of the tube to a low impedance, enabling maximum power transfer to the low impedance load.
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post #23 of 82 Old 07-09-2009, 09:24 AM
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Maybe. Like I said, I was speculating. I know that the resistance of a speaker cable changes the effective output impedance (or, if you prefer damping factor) in the amp-to speaker connection. Outside the amp, it doesn't change the amp proper, but it does change the system as a whole. Just seemed to me that the output transformer is like coiling a very long speaker cable inside the amp instead of outside it - - and that the resulting added resistance would have the same effect in front of the output terminals as it would have had after them. But again that's just me thinking out loud.
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post #24 of 82 Old 07-09-2009, 09:38 AM
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Tubes don't inherently produce even-order harmonics. You can make a transistor or vacuum tube circuit produce even-order harmonics. You can also make one produce odd-order. You can make one produce both. For amplification, and not effects, I prefer a circuit that produces as close to neither as possible, even when I listen to electronic-sounding recordings (like Tangerine Dream) or mechanical-sounding ones (like Andre Watts).

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post #25 of 82 Old 07-09-2009, 09:56 AM
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Quote:
Originally Posted by tvrgeek View Post

I highly recommend reading David Manley's book on tubes. (VTL).

Morgan Jones' two books are also must reads. DM abuses valve specs a little too hard for my tastes.

Quote:
Originally Posted by tvrgeek View Post

Circuit implementation has more to do with it than the actual component. You can make a good or bad amp with either.

Agree. The expression 'tube sound' makes me cringe.

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Originally Posted by tvrgeek View Post

If the unit does anything other than amplify, it is not just an amp, it is a distortion generator. Some may like it, some may not. Personal preference is just that, personal.
"Better" is preference. Accuracy is objective and can be measured. The physics are not a mystery, they are well understood.

Agreed, but not something many audiophiles understand.

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Originally Posted by duvetyne View Post

Hence the use of impedance matching transformers on the outputs.

Still doesn't give a near zero output Z. Best tube amp I ever measured in this regard was a bit under an ohm in the midband and as expected worsened at both ends. My Fisher receiver, even with a fair whack of gNFB is still about 2R and the zero gNFB amps I designed varied between 2 and 4R.

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Originally Posted by duvetyne View Post

No transformer can alter the characteristics of a tube. The transformer is an impedance transformer, it is used to transform the high output impedance of the tube to a low impedance, enabling maximum power transfer to the low impedance load.

No, but the two work together to produce a composite transfer function. The transformer is not perfect and primary and leakage inductance as well as shunt capacitances will affect how i works at a given frequency in a real application.
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post #26 of 82 Old 07-09-2009, 10:04 AM
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Originally Posted by Drew Eckhardt View Post

Sure. Identical transfer functions sound identical. Differences less than thresholds of perception sound identical. That means amplitude response, distortion, and noise.

True and the Carver Challenge showed it to be so, but many still won't accept it's true. Leaves too little room for lots of grandiose descriptions and playing pseudo reviewer.

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Originally Posted by Drew Eckhardt View Post

It's better because:

and MOST important.

5) Tubes have pretty glows. Especially with tube rectification where you can get more than just heater orange and blue from Cherenkov radiation.

Note mesmerizing glow from mercury vapor rectifiers. Pretty!


I like thoriated tungsten filaments better. Four of these in stero PP, and I could read the paper with them. I'd be a bit concerned if I could do that with a SS amp.

LL
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post #27 of 82 Old 07-09-2009, 10:06 AM
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Originally Posted by Chu Gai View Post

Ultra short signal path. Yeah, those electrons hate going round and round.

Yeah, it made the 47Labs Gaincard sound so much better than a typical NatSemi LM series poweramp chip. /sarcasm
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post #28 of 82 Old 07-09-2009, 11:13 AM
 
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Quote:


Still doesn't give a near zero output Z.

Nothing on this planet does. No-one ever suggested an zero Ohm output impedance either, in fact, I mentioned impedance matching, which would imply an 8 Ohm output impedance.

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Just seemed to me that the output transformer is like coiling a very long speaker cable inside the amp instead of outside it

You're not considering transformer theory. If you view it as just a coil of wire, you'd see that it's a 'direct short' across the amplifier output.
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post #29 of 82 Old 07-09-2009, 12:28 PM
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Isn't the primary more like a resistor of X ohms across the amplifier output? But more to my point, doesn't the current induced in the secondary have to flow through the winding, so that it "sees" whatever resistance that winding presents?

Didn't come here to argue about something I don't necessarily think matters. My primary point was that the higher output impedance of typical tube amps creates greater frequency response anomalies than the lower output impedance of typical transistor amps when pushing real-world speakers with significant impedance variation, an issue that I just don't think is controversial. Tube amps are tested from their output terminals, post-transformer, and the transformers clearly have not eliminated the output impedance issue . . .
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post #30 of 82 Old 07-09-2009, 12:45 PM
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Quote:
Originally Posted by duvetyne View Post

Nothing on this planet does.

A typical SS amp is as near as, usually <100milliohms at the terminals.

Quote:
Originally Posted by duvetyne View Post

No-one ever suggested an zero Ohm output impedance either, in fact, I mentioned impedance matching, which would imply an 8 Ohm output impedance.

Why would you want an 8R output impedance except for a very specific amp/speaker combo? It still should be as low as possible for an amplifier that is expected to drive a variety of speakers.
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