Why Tubes?

[leonski]

I've gotten really interested lately in tubes and tube amps.
Besides the obvious differences, especially in a dark room, what else can be said?

Some talk about he difference in distortion products.   Even VS Odd harmonics.   That sort of thing.

But I looked at the Power Supplies.   THIS is a real eye opener.      Tubes ALWAYS have full PS voltage applied to them.

Not like SS which turns the voltage on / off basically in time to the music.      

One thing which caught my eye were the smaller capacitors in tube amps.     Certainly nothing like the number or capacity of SS gear.


When I checked into that?   Here's what I found.    While capacitance is important, the VOLTAGE is what really drives what matters.

It 'is NOT capacitance, but ENERGY.   Usually expressed in Joules.   A 100mfd cap @500volts has about the same energy as 4000mfd @80volts for a SS amp.
Energy stored rises VERY quickly with voltage.           .  

This is where Voltage or Current source amps and the difference start.   Tubes seem to always have the full voltage applied while SS is biased to an slight 'on' state and floats from there.... 

Just be CAREFUL when messing around under the hood of a tube amp.    500v will REALLY smart if you zap yourself.

Somebody with more informatin might want to add to this, but for now?    I'm satisfied with just the first layer.    

[novisnick]

Tubes scratch that itch!
                                                             Its just that simple for me! 😍

[audiobill]

Leonski, a transistor is basically an underdriven switch, where a tube has much higher voltage swings before clipping.

And, should electrons grind their way through broken glass (silicon) or float freely through a vacuum on their way from cathode to plate?

I’ll don my flame retardant suit in anticipation of @keithl tired “accuracy” arguments!

[DavidR]

Bill, I don't believe that tube amps clip a signal. They roll off the signal where as a SS amp will push it through and clip the signal.

[RichGuy]

The most accurate, most detailed, most musical and simply the best sounding equipment I've had in my system all have tubes.

I love my  MHDT Stockholm balanced NOS tube DAC,  my PS Audio BHK Signature tube preamp and my Woo Audio WA-6 tube headphone amp. When done well tube equipment sounds amazing.

[405x5]

I hope SOON 🔜 they will come out with ATMOS TUBES…..so I can enjoy that warm illuminated glow floating over my head

[audiobill]

Aug 10, 2021 20:11:07 GMT -5 DavidR said:

Bill, I don't believe that tube amps clip a signal. They roll off the signal where as a SS amp will push it through and clip the signal.

David, ultimately the signal will flatten to B+ and ground or equivalent, but a tube gets there through a less violent process.

[audiobill]

Aug 10, 2021 20:27:05 GMT -5 405x5 said:

I hope SOON 🔜 they will come out with ATMOS TUBES…..so I can enjoy that warm illuminated glow floating over my head

Is Atmos high fidelity? Does it occur in nature? By what instrument?

Seems artificial to me. You know, synthesized.

[leonski]

Aug 10, 2021 20:27:05 GMT -5 405x5 said:

I hope SOON 🔜 they will come out with ATMOS TUBES…..so I can enjoy that warm illuminated glow floating over my head

Put another pinch in the bong.   You'll get there........

[leonski]

Here is an article from ELLIOT SOUND PRODUCTS. This guy seems to know his stuff and I've read bunches of his mini-articles.

sound-au.com/valves/clipping.html

This one on the 'simple' subject of clipping......

[donh50]

A tube amp when heavily overdriven clips just like a SS amp. Often with worse distortion due to hysteresis in the output transformer. Because of the nature of their circuit gain stages, a tube amp will usually "round" the signal more as it approaches clipping compared to a SS amp. This has more to do with the amount of feedback used in a SS amp compared to tube circuits -- SS amps usually have much higher internal (loop) gain, which allows greater feedback, which provides lower distortion, lower output impedance, higher input impedance, and so forth. SS designs also tend toward differential internal stages, which suppress even harmonics, while single-ended tube designs do not. Tube designs usually have higher distortion and it begins with the second harmonic, which generally leads to more "benign" sounding distortion than the third harmonic that dominates SS designs. The catch is that the SS designs' distortion is usually much lower than that of the tube design.

An endless debate... IME/IMO, most of the "tube sound" is not intrinsic to the tubes themselves, but rather a consequence of other design choices, like single-ended topology and transformer coupling. No reason a tube design should not sound the same as SS or vice-versa, but the market demands "tube sound". It is not too hard to change a SS amp to sound like a tube amp, and a properly designed tube amp will sound similar to a SS amp with similar performance (low distortion and all that jazz).

Doing blind tests with tube vs. SS amps can be humbling as often they sound indistinguishable. When I was doing such things, I found the biggest factor was from tube amps' generally much higher output impedance, which meant frequency variations into speakers that was picked up in blind AB or ABX testing. Simply sticking a resistor in series with the output of the SS amp was enough to make them indistinguishable most of the time. As I said, humbling, to find out my nice ARC tube amp could be emulated by a fairly cheap little SS amp, and least sonically.

Interesting factoid: The mathematical series expansion of a tube's distortion series is factorial, while for a bipolar transistor it is exponential. That means distortion rises faster in a transistor than in a tube. In the real world, other factors than intrinsic device characteristics dominate the overall performance, natch.

FWIWFM - Don

[KeithL]

Dolby Atmos is not "a thing" - it is simply a way to encode and reproduce a whole bunch of audio channels.

By your definition "stereo" isn't natural either... unless you know of an instrument that produces sound specifically out of two symmetrically arranged holes.

(Actually, with some speakers, all of the frequencies unnaturally come from one location while, with others, they are unnaturally reproduced from different points for different parts of the frequency spectrum.)

For a sound that originates anywhere other than directly in front or in back of you stereo does not actually reproduce the sound "as if you were there".

The most trivial example demonstrates this quite adequately.

Let's assume you have a single singer, standing center stage, in a relatively large room, which is symmetrical.

The sound of her voice will reach both of your ears at about the same time.

Then, slightly later, you will hear the echoes of her voice that reflect from the left and right walls... again arriving at the same time (because everything is symmetrical).

(For now let's also ignore the vertical aspects as well.)

Now let's listen to a STEREO recording of that singer...

Instead of her voice coming from one spot directly in front of you it will be coming from two spots, the speakers, one ahead and to the left, and the other ahead and to the right.

The sound from the left speaker will reach your left ear about one millisecond before it reaches the right ear...

And the sound from the right speaker will reach your right ear first...

Remember that, with the live performance, it reached both ears at the same time.

Now let's look at the "first reflections"...

The left speaker is much closer to the left wall and much further from the right wall...

Whereas the right speaker is much closer to the right wall and much further from the left wall...

As a result, when considering those first echoes, there will be TWO first echoes from the right wall, and TWO from the left wall...

And they will not be arriving at the same time...

So now, instead of a single "first arrival echo", as there was with the live performance, there will be two, separated by a difference in time.

Yet we humans generally fail to notice, or learn to ignore, all of those discrepancies...

The only way to actually even approach the experience of the original performance would be to use a single monaural speaker in place of each performer or instrument...

Or to use headphones, and a binaural recording, and so remove the listening room from the equation altogether.

And we needn't even bother to consider too deeply that any live recording will contain information related to the room acoustics of the original venue...

And, unless your listening room is identical to it, your listening room will add aspects of ITS room acoustics, which will be different...

(Someone once compared this to using a projector to project a movie onto a wall with a mural painted on it.)

If you ignore the DSU - which is used to SYNTHESIZE surround sound - Dolby Atmos doesn't DO anything at all...

It merely enables the audio engineer to more carefully control the directions and other aspects of individual sounds...

Therefore, in theory, it could enable an engineer to more accurately reproduce an original or live performance...

However, as with any other tool, that offers no assurance that this will be his or her goal...

Or that, even if it is, that they will do it WELL or EFFECTIVELY...

As you add more channels any recording medium becomes more complex...

So, with the opportunity to reproduce something more accurately, or more effectively craft something from scratch...

Comes the opportunity to mess it up in newer and more interesting ways.

Aug 10, 2021 21:04:47 GMT -5 audiobill said:

Aug 10, 2021 20:27:05 GMT -5 405x5 said:

I hope SOON 🔜 they will come out with ATMOS TUBES…..so I can enjoy that warm illuminated glow floating over my head

Is Atmos high fidelity? Does it occur in nature? By what instrument?

Seems artificial to me. You know, synthesized.

[KeithL]

Your first assertion is only partly true...

Most solid state designs tend to clip rather abruptly - producing clipped waveforms with perfectly flat tops.

Tubes tend to clip more gradually - producing waveforms that get gradually "flatter and flatter on top".

However, with tube amplifiers, this tends to occur gradually, as you overdrive the amplifier more and more.

Whereas, with solid state amplifiers, it tends to occur suddenly, at a specific point.

And, yes, this is due in large part to how much feedback is used, and  it is technically possible to "make a tube amp that behaves like a solid state amplifier" in terms of things like overload...

However, some of the intrinsic characteristics of tubes cause it to be somewhat difficult to do so, which is why it rarely occurs...

(ARC expended a lot of effort to make their tube products sound almost as accurate and distortion free as much more economical solid state products.)

For example there is a very significant TECHNICAL reason why you cannot use large amounts of global feedback with tube amplifiers - even if you want to.

The phase shift present in the output transformer will cause your amplifier to be unstable and oscillate if you apply more than a limited amount of feedback around it.

This leaves you with the paradoxical limit of not being able to apply enough feedback to completely counteract the non-linearity of the transformer.

The only way to avoid this is to avoid using the output transformer or to limit the amount of feedback you use around it.

And, if you eliminate that transformer, then you have to deal with the huge mismatch between the plate impedance of an typical output tube and the load impedance of a typical speaker.

(At maximum plate dissipation, without an output transformer, a single KT88 could deliver about 1/2 watt to an 8 Ohm speaker.)

There are OTL (output transformerless) tube amplifiers that have gone this route...

But they tend to be big, heavy, complex, expensive, and require a LOT of tubes to generate any significant amount of output power.

(Remember Futterman...?)

Another interesting thing, and one of the reason why many people perceive triode amplifiers in particular as being "very dynamic" and "sounding more powerful than they are", is that distortion curve.

As you mentioned a typical solid state amplifier will have very low distortion until it gets closer to clipping.

(A "typical" 10 watts solid state amp might produce 0.1% THD at 0.1 watts, 0.05% THD at 1 watt, 0.05% THD at 10 watts, and 10% THD at 12 watts.)

In contrast, a tube amp, with very little feedback, has a monotonic distortion product...

(A "typical" 10 watt SET amplifier might produce 0.1% THD at 0.1 watts, 1% THD at 1 watt, 10% THD at 10 watts, and 12 % THD at 12 watts.)

HOWEVER, in addition to actual power, we humans tend to PERCEIVE distortion as "loudness".

(That's how that 2 watt table radio can sound loud enough to make you run for cover.)

As a result, both amplifiers sound equally loud at 0.1 watts, where the distortion is relatively low on both...

But, when you turn them up, the SET amp, producing 10 watts at 10% THD, sounds much louder than the solid state amplifier, producing 10 watts at 0.05% THD...

The result, to the human ear, (and ignoring the distortion itself), is that at 10 watts the SET amplifier "sounds more powerful"...

So the overall effect is similar to applying an artificial "dynamic range expander" (which "leaves quiet sounds alone but makes loud sounds seem louder".)

But, of course, it is merely a "special effect" that makes the tube amp seem "more dynamic"... although it can in fact sound quite pleasant.

(And in fact it may help to counteract the perceived effect of the excessive compression used on many modern albums.)

(And, even more fortunately, that 10% THD is mostly second harmonic, so it is relatively benign as well.)

The reality is that ARC was one of the relatively few companies who actually tried, and succeeded, in producing tube amplifiers with relatively high fidelity and low distortion...

But, if you're looking for high accuracy, and low distortion, using tubes and transformers is the long and expensive path to that goal these days...

Aug 12, 2021 13:40:35 GMT -5 donh50 said:

A tube amp when heavily overdriven clips just like a SS amp. Often with worse distortion due to hysteresis in the output transformer. Because of the nature of their circuit gain stages, a tube amp will usually "round" the signal more as it approaches clipping compared to a SS amp. This has more to do with the amount of feedback used in a SS amp compared to tube circuits -- SS amps usually have much higher internal (loop) gain, which allows greater feedback, which provides lower distortion, lower output impedance, higher input impedance, and so forth. SS designs also tend toward differential internal stages, which suppress even harmonics, while single-ended tube designs do not. Tube designs usually have higher distortion and it begins with the second harmonic, which generally leads to more "benign" sounding distortion than the third harmonic that dominates SS designs. The catch is that the SS designs' distortion is usually much lower than that of the tube design.

An endless debate... IME/IMO, most of the "tube sound" is not intrinsic to the tubes themselves, but rather a consequence of other design choices, like single-ended topology and transformer coupling. No reason a tube design should not sound the same as SS or vice-versa, but the market demands "tube sound". It is not too hard to change a SS amp to sound like a tube amp, and a properly designed tube amp will sound similar to a SS amp with similar performance (low distortion and all that jazz).

Doing blind tests with tube vs. SS amps can be humbling as often they sound indistinguishable. When I was doing such things, I found the biggest factor was from tube amps' generally much higher output impedance, which meant frequency variations into speakers that was picked up in blind AB or ABX testing. Simply sticking a resistor in series with the output of the SS amp was enough to make them indistinguishable most of the time. As I said, humbling, to find out my nice ARC tube amp could be emulated by a fairly cheap little SS amp, and least sonically.

Interesting factoid: The mathematical series expansion of a tube's distortion series is factorial, while for a bipolar transistor it is exponential. That means distortion rises faster in a transistor than in a tube. In the real world, other factors than intrinsic device characteristics dominate the overall performance, natch.

FWIWFM - Don

[donh50]

@keithl I started to go into global versus local feedback, how to compensate the output transformer, and all that jazz but ain't hardly worth it. The Lounge is not a branch of the IEEE or AES (nor should it be). I have designed tube amps, and preamps, and have some idea what it takes to get them to sound alike, That's not usually the goal, natch, at least not for Marketing (which usually trumps Engineering). (*)

I do remember Julius and his amps (each one pretty much an individual, for better or worse, and reliability was often meh). Not sure what happened to NYAL, but Atma-Sphere has picked up the OTL torch with modern designs that work well by all accounts (and Ralph is a very nice guy).

As for me, I sold my ARC amp and went SS on all channels. Still have my old ARC preamp; need to remove my modifications and sell it at some point, but too lazy to dig it out of storage.

Onwards - Don

(*) Years ago, in college, I built a tube preamp that was differential, with active biasing and loads, some fancy feedback/feedforward circuitry, and such. Specs were great, comparable and in some ways better (e.g. input overload was much higher) than the SS preamps of the day, but listeners felt it was "too solid-state". Go figure. I did manage to sell it. My first tube power amp was a mess; I learned about blocking distortion the hard way, then tried an active cathode biasing scheme that managed to blow up a bunch of tubes when a transistor failed in the biasing compensation circuit and let the current grow essentially unbounded.

[DavidR]

All this fuss about clipping. It brings to mind my old theory: make sure your amp can handle your speakers and what they require.

 

[leonski]

Aug 12, 2021 13:40:35 GMT -5 donh50 said:

A tube amp when heavily overdriven clips just like a SS amp. Often with worse distortion due to hysteresis in the output transformer. Because of the nature of their circuit gain stages, a tube amp will usually "round" the signal more as it approaches clipping compared to a SS amp. This has more to do with the amount of feedback used in a SS amp compared to tube circuits -- SS amps usually have much higher internal (loop) gain, which allows greater feedback, which provides lower distortion, lower output impedance, higher input impedance, and so forth. SS designs also tend toward differential internal stages, which suppress even harmonics, while single-ended tube designs do not. Tube designs usually have higher distortion and it begins with the second harmonic, which generally leads to more "benign" sounding distortion than the third harmonic that dominates SS designs. The catch is that the SS designs' distortion is usually much lower than that of the tube design.

An endless debate... IME/IMO, most of the "tube sound" is not intrinsic to the tubes themselves, but rather a consequence of other design choices, like single-ended topology and transformer coupling. No reason a tube design should not sound the same as SS or vice-versa, but the market demands "tube sound". It is not too hard to change a SS amp to sound like a tube amp, and a properly designed tube amp will sound similar to a SS amp with similar performance (low distortion and all that jazz).

Doing blind tests with tube vs. SS amps can be humbling as often they sound indistinguishable. When I was doing such things, I found the biggest factor was from tube amps' generally much higher output impedance, which meant frequency variations into speakers that was picked up in blind AB or ABX testing. Simply sticking a resistor in series with the output of the SS amp was enough to make them indistinguishable most of the time. As I said, humbling, to find out my nice ARC tube amp could be emulated by a fairly cheap little SS amp, and least sonically.

Interesting factoid: The mathematical series expansion of a tube's distortion series is factorial, while for a bipolar transistor it is exponential. That means distortion rises faster in a transistor than in a tube. In the real world, other factors than intrinsic device characteristics dominate the overall performance, natch.

FWIWFM - Don    

What I HEARD at shows was that the BEST of SS and Tube sounded remarkablly similar.    I wouldn't know if I could tell 'em apart in blind listening.   As long as you didn't try to cause hearing damage to the listeners.

But one thing that DOES seem real is that the speakers for tube / SS have differences.    Damping is one.    Tubes work well with speakers that have high internal damping.    SS likes to be the damping.....Thus the high damping factor.

Might be other differences as well.    I'm not convinced that tubes handle highly reactive loads as well as SS.      But ONE thing which Does seem correct is that the BEST designs of transformers DO provide wide bandwidth.   

I'd be curious to know why I see nearly ZERO Toroids in Tube Gear.     Either power or output.      And Why Not a switcher in a tube amp?   Could THAT be made to work?   To any advantage?

And while lots of people are hung-up on distortion and such, maybe we want to at least ALSO look at 10khz Square Wave response?  

[DavidR]

Aug 12, 2021 19:05:38 GMT -5 leonski said:

What I HEARD at shows was that the BEST of SS and Tube sounded remarkablly similar.    I wouldn't know if I could tell 'em apart in blind listening.   As long as you didn't try to cause hearing damage to the listeners.

But one thing that DOES seem real is that the speakers for tube / SS have differences.    Damping is one.    Tubes work well with speakers that have high internal damping.    SS likes to be the damping.....Thus the high damping factor.

Might be other differences as well.    I'm not convinced that tubes handle highly reactive loads as well as SS.      But ONE thing which Does seem correct is that the BEST designs of transformers DO provide wide bandwidth.   

I'd be curious to know why I see nearly ZERO Toroids in Tube Gear.     Either power or output.      And Why Not a switcher in a tube amp?   Could THAT be made to work?   To any advantage?

And while lots of people are hung-up on distortion and such, maybe we want to at least ALSO look at 10khz Square Wave response?  

I collect and restore Acoustic Research speakers. The only big difference between listening with my 60wpc Bob Latino ST-120 tube amp and my 500wpc Emo SA-250 is the bass response. Emo amp has high damping factor and the bass response is 'tighter' as they say.

[ttocs]

^^^^ 4 posts up: Krell MRA, 16KW @0.5Ω (assuming it's provided with enough electricity). 683 lbs

[DavidR]

Aug 12, 2021 19:39:45 GMT -5 ttocs said:

^^^^ 4 posts up: Krell MRA, 16KW @0.5Ω (assuming it's provided with enough electricity). 683 lbs

MRA  MONO BLOCK

www.ebay.com/itm/265190047602?hash=item3dbe8eff72:g:-QMAAOSw6p5gx8b~

[donh50]

Aug 12, 2021 19:05:38 GMT -5 leonski said:

What I HEARD at shows was that the BEST of SS and Tube sounded remarkablly similar.    I wouldn't know if I could tell 'em apart in blind listening.   As long as you didn't try to cause hearing damage to the listeners.

But one thing that DOES seem real is that the speakers for tube / SS have differences.    Damping is one.    Tubes work well with speakers that have high internal damping.    SS likes to be the damping.....Thus the high damping factor.

Might be other differences as well.    I'm not convinced that tubes handle highly reactive loads as well as SS.      But ONE thing which Does seem correct is that the BEST designs of transformers DO provide wide bandwidth.   

I'd be curious to know why I see nearly ZERO Toroids in Tube Gear.     Either power or output.      And Why Not a switcher in a tube amp?   Could THAT be made to work?   To any advantage?

And while lots of people are hung-up on distortion and such, maybe we want to at least ALSO look at 10khz Square Wave response?  

Sounds like Keith is the expert, but here is my take based upon my experience with them over the years:

Damping factor is the inverse of output impedance, and is IME/IMO the primary distinguishing characteristic of tube amplifiers. Their much higher output impedance makes them more sensitive to the load (speaker) and also means they will struggle more, or at least sound different driving, reactive loads. I think I mentioned that in my first post.

Toroids are good for constraining the EM fields around them, which is good for tightly-packed components since they generate less noise near them, but toroids are not as efficient as conventional (EI) transformers. Toroids also do not usually have a core gap, which makes them more sensitive to any DC on the power line and increases their hysteresis. The latter is not usually a big deal in a power transformer, but increases distortion in an output transformer, and as Keith noted low loop gain and limited bandwidth (greater phase shift) makes it harder to use feedback to suppress that hysteresis. So, space is not a big concern, and you can get more power in the same size transformer (or a smaller transformer for the same power), with less distortion, using conventional EI transformers.

A number of tube amplifiers have very extended HF response at low power, but it tends to decrease as power increases, more so than for SS amps IME.

There are some challenges with switch-mode power supplies (SMPS) in tubes due to the very high voltages required, and I suspect there is not much to argue for them. You still need output transformers, and with low-level stages typically in class A plus all those filament heaters, not much benefit in a SMPS in a tube amp. There have been a few papers on tube class D amplifiers, but AFAIK they have never been commercialized.

Most reviews include HF square waves, at least I seem to recall Stereophile showing them? Don't quote me on that...

FWIWFM - Don