What does tube equipment sound like?

[KeithL]

Tube equipment sounds distinctly different than solid state equipment.
(Face it, solid state equipment is usually cheaper, and often has better long-term reliability. If tube equipment didn't sound different, then nobody would buy it... right?)

I know some people who love the way tube equipment sounds, but I've also met a few who bought a tube amp, listened to it, and hated it. Some of them bought their tube equipment - without ever hearing any - based on some review they read that said "it sounded great" or "real audiophiles like tubes". Tube lovers seem to always insist that tubes sound "warm" or "organic" and solid state equipment sounds "cold" or "analytical". Solid state aficionados, in contrast, usually describe tube equipment as sounding "mushy" or "syrupy", and take the term "analytical" as a compliment. In this thread, I'm going to try to unscrew the inscrutible and describe - in words - what tube equipment sounds like.

We here at Emotiva now make both solid state and tube equipment. So, unlike some companies who have a vested interest in "selling" you one or the other, we want you to make an informed decision: that way we get a happy customer - which is good for both of us. Obviously, the best way to know what tube equipment sounds like is to listen to it.

I'm also going to include a few of the reasons why tube equipment sounds like it does, however I do not want to start an engineering discussion on THIS thread.

[GreenKiwi]

Well, some of them look pretty cool too.

At least in my experience I have found the upper mid range to seem maybe a little warmer and to have the appearance of better imaging.

[DYohn]

To me, "tube sound" implies a slight emphasis in the upper bass through low midrange, increased even-order harmonics below about 3500Hz and a first order roll-off above 12KHz. AKA "analog warmth."

[KeithL]

TUBES ADD A CHARACTERISTIC COLORATION TO THE SOUND

I just wanted to say that and get it over with.

Some companies who sell tube equipment (and some individuals who like tube equipment) seem determined to sell a myth: that myth is that tube equipment is somehow more accurate than solid state equipment. Using the literal (dictionary) definition of the term "accurate", this is simply not true. Most good solid state equipment has lower overall distortion and noise than even the best tube equipment; this is simply a fact. Now, you might make a case that the distortions and colorations added by tube equipment somehow make the resulting audio sound more realistic (maybe these distortions were originally there in the live performance, the recording chain removed or lost them, and we're putting them back)... but the fact remains that the sound is being changed from what's there in the recording.

Now that we're past that, let's agree that the reality is that a lot of people simply LIKE the way tubes sound. Hey, 5700 degree daylight white bulbs are more accurate than warm white, but a lot of people prefer warm white for their livingroom; and a lot of folks like the tast of grape juice after it's spoiled a lot better than the fresh stuff (just check the prices at the latest wine auction). Once you accept that tubes color the sound you can move on to how and why they do so, and decide whether you do or don't like it.

[mgbpuff]

I agree with DYohn that 'tube sound' as he describes it is what most people think. But not all tube equipment has that sound - some are indistinguishable from solid state sound. There are many different tubes with many characteristic curves some very linear over a wide range, some not so. Also circuit topologies (pp, set, etc) are often more responsible for the sound than the amplifying device be it tube or SS. Audio Research is known for its linearity and neutral (ss like) sound. Conrad Johnson is known more for the tube bloom that DYohn describes, and so on. Pass is known for its Class A ss designs which many compare to the best tube set designs. Now perhaps the output circuits cause a lot of this difference because tubes typically use transformers and ss does not need them, but there are OTL tube designs also.

[KeithL]

DISTORTION CURVES AND SPECTRA

Different devices and types of circuits produce different distortions; both different amounts and different types of distortion.

At low power levels, most modern solid state amplifiers produce very VERY little distortion (this wasn't always true in the "bad old Class B days"). It's fair to say that the distortion produced by most modern solid state amplifiers at a few watts is totally inaudible to any human (and most bats). [Even if you can hear it, it is very VERY subtle; far more subtle than the obvious difference between tubes and solid state.] As you start to increase the volume, the distortion remains very low until you reach some power limit, at which point it jumps up suddenly (this is the clipping point). Once the amp starts to clip, the distortion rises very rapidly, and is made up of a mix or harmonics, including a lot of "higher order" harmonics. It sounds nasty; which is why you want to avoid turning your amplifier up that loud. Luckily solid state amps with oodles of power are relatively cheap, so you just need to get an amplifier that's powerful enough that you'll never hear it clip.

Tube amplifiers behave rather differently. They tend to produce higher levels of distortion, even when playing quietly, and their distortion tends to rise as you turn them up (this is called "a monotonic distortion curve"). Fortunately, the distortion produced by many tube amplifiers consists more of lower order harmonics (with some designs this is mostly second harmonic), which sound less offensive than high-order harmonics. Adding second harmonic distortion to audio tends to make it sound "warm" or "full" (there are commercial sound processing devices designed to do this; check out Aphex). Our human ears also tend to interpret distortion as "loudness" (which is why a 1 watt table radio can get so loud). This means that the gradually increasing distortion form a tube amp makes it sound even louder than it is when you turn it up very high. This makes low power tube amps sound more powerful than they really are. It also produces the illusion that the music is more dynamic. [The loud spots are really louder, but they are also more distorted, which makes them seem "even more louder" than they really are; the result is the psychoacoustic equivalent of a dynamic range expander - and can sound quite pleasant with some music.] Since listening is all illusion anyway, this can make the music sound "livelier" and more dynamic.

Now, remember that most solid state amplifiers don't produce significant audible distortion at normal listening levels. Because tube amps DO produce audible distortion, with them it matters what kind (or "flavor") of distortion they produce. Pentode amplifiers, and amplifiers with lots of feedback, tend to produce less distortion - but many tube aficionados find it somewhat unpleasant. Triode amplifiers, especially single ended triodes with low or no feedback, tend to actually produce a LOT more distortion (some as much as 10% at full rated output), but some tube lovers find it to be more pleasant distortion.

[DYohn]

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[KeithL]

Indeed.... but that does beg the question: "Why bother with tubes if they sound the same?"

I've heard plenty of tube preamps that sound very neutral; since they aren't exorbitantly expensive (relatively), that makes them sort of a neutral choice option. However, between having output transformers, and lower damping, tube power amps are usually quite different sounding... you would NOT mistake a pair of Black Beauties for an XPA-2 - even for a second. Anyone who buys a pair of Black Beauties should buy them because they like that characteristic tube sound; if they want neutral sound, then they should buy an XPA-2. And tube power amps, especially high-powered ones, tend to be much more expensive than their solid state equivalents - so why pay the extra money unless you hear a difference that you like?

Some vendors also go beyond design results and deliberately exaggerate the "tubey-ness" of their products. The Schiit Lyr, and some of the Yaqin triode amps, come to mind.

Jun 10, 2013 11:11:28 GMT -5 mgbpuff said:

I agree with DYohn that 'tube sound' as he describes it is what most people think. But not all tube equipment has that sound - some are indistinguishable from solid state sound. There are many different tubes with many characteristic curves some very linear over a wide range, some not so. Also circuit topologies (pp, set, etc) are often more responsible for the sound than the amplifying device be it tube or SS. Audio Research is known for its linearity and neutral (ss like) sound. Conrad Johnson is known more for the tube bloom that DYohn describes, and so on.

[mgbpuff]

So Keith, you're saying that if you compare the most linear part of the characteristic curves of the best of tubes to the characteristic curves of the most ordinary of ss devices, the ss are more linear and thus cause less amplification distortion? My understanding is that McIntosh, a highly revered brand, uses output transformers even for their ss amplifiers.

[DYohn]

Jun 10, 2013 11:36:00 GMT -5 KeithL said:

Some vendors also go beyond design results and deliberately exaggerate the "tubey-ness" of their products. The Schiit Lyr, and some of the Yaqin triode amps, come to mind.

And SET amps, which are my personal preference.

[KeithL]

A little bit of both.

I'm trying to educate our customers so they can make the choice that's best for them.

There is WAY too much hype around lately about tubes - and a lot of it is just plain untrue. I want someone to buy a tube amp because they know what tube amps sound like, and enjoy that sound. I do NOT want them to buy a tube amp just because they read somewhere that "tubes sound good". And I certainly don't want them to buy it because they read somewhere that tubes are somehow (magically?) "better".

I have spoken to a few customers who bought tube equipment because they were told that, if they liked the way good solid state equipment sounded, then tube equipment was "the next step up" - and one or two of them were quite disappointed when their new tube equipment sounded entirely different. I don't want this to happen to OUR tube customers. (And, yes, some were happy with the difference.)

It is certainly a discussion (otherwise I would have locked it).... but I would prefer to keep it in the direction of describing what tube equipment sounds like. That does include why you do or don't like the way tube equipment sounds, and absolutely includes comments like yours about how wide the difference between them is (or sometimes isn't), but I want to avoid a bare-knuckle debate about which is better.

Jun 10, 2013 11:32:28 GMT -5 DYohn said:

So... is this a lesson and not a discussion?

[DYohn]

Understood, and appreciated. This is why when people ask me about tubes I always tell them it's different strokes for different folks. I never use tubes in HT, it's exclusively solid state for the high watts-per-dollar and fast transient response with low distortion that only a SS amp can provide, but I prefer using tubes in my 2-channel system because I like the sound of analog warmth and what that does to most music. But as in all things audio, the best thing to do is "Try it, you might like it. Just ignore the hype and you'll be alright." And if you find that you hate the result, the used market is hot.

[arthurz]

I just found this plugin that purports to simulate tube distortion. Based on my experience with the Bellari HA540, it actually sounds reasonably realistic: nickcrowlab.tk/

[KeithL]

First off, this is a bit of a historical discussion... McIntosh has recently been bought, and has been making solid state home theater equipment for years, so "the old McIntosh" is long gone. Before that, McIntosh built their reputation on very good build quality and a truly amazing lifetime unconditional warranty. They also developed their own proprietary (and very good) transformer design for tube equipment - and circuitry to go with it (you can Google "unity coupled"). Because of their build quality, and their unique transformer design, their tube equipment did indeed sound very good. It was also incredibly reliable (but then, with a lifetime warranty, it should be) - and VERY expensive.

When they switched over to solid state they retained the transformers because they believed the benefits outweighed the disadvantages. The benefits of transformers include the ability to deliver full rated power into different loads, and protection from DC reaching the speakers in the event of an output-device failure (both of these were significant advantages in the early days of solid state); the disadvantages include much higher cost, much higher weight, poorer frequency and phase response, and higher distortion. McIntosh's amplifiers with output transformers CANNOT deliver the sound quality - or specs - of most modern (transformerless) designs. McIntosh's early solid state tuners were truly exceptionally good sounding; their solid state preamps and power amps sounded good, but were more exceptional for their reliability and build quality.

I'm not going to delve into the engineering..... but......

As individual devices, tubes are actually more linear than transistors. However, most modern designs use feedback to lower distortion; when applied properly, feedback can reduce distortion a lot. Tube power amps (with their output transformers) are limited in the amount of feedback they can safely use; solid state designs much less so. Therefore, feedback can be very effectively used to reduce the distortion and non-linearities in solid state circuits to way below the values that can be achieved with tubes. (And, no, feedback, WHEN PROPERLY DONE, does nothing to degrade sound; although, when improperly done, it's another story.)

Jun 10, 2013 11:38:30 GMT -5 mgbpuff said:

So Keith, you're saying that if you compare the most linear part of the characteristic curves of the best of tubes to the characteristic curves of the most ordinary of ss devices, the ss are more linear and thus cause less amplification distortion? My understanding is that McIntosh, a highly revered brand, uses output transformers even for their ss amplifiers.

[KeithL]

HOW TUBE PREAMPS SOUND

Tube preamps are relatively simple devices. Because a preamp is a line level high impedance device, they don't need output transformers. Tube preamps tend to sound less "tubey" than tube power amps - and more like their solid state equivalents. While it is possible to build a tube preamp with lots of feedback (which would probably make it sound even more like a solid state one), most tube preamps are built with little (or even no) feedback. Most tube preamp circuits are also single ended, class A, triode designs; because it's a preamp, these design types have none of the drawbacks they have in a power amp. (Note that it is NOT expensive or complicated to make a single ended, class A, triode preamp.)

By varying the bias, operating voltage, and circuit topology, it is possible to vary the amount and type of distortion they have - which is why, even though some tube preamps sound pretty much like a solid state one, others do indeed sound "tubey".

The harmonic content added by the tubier sounding preamps is often described as sounding "warmer", or "fuller", or sometimes as being "more organic". (Usually the opposite of "cold" and "analytical".) It is usually most noticeable in the midrange and upper frequencies. Some tube preamps also "soften" the bass, but not all do.

Depending on the circuit design, some tube preamps sound noticeably different when different tubes are used (the circuitry interacts with the capacitance, gain, and other characteristics of the tubes). Many tube lovers have lots of fun trying out different brands of tubes (and certain "well beloved" brands and types, especially vintage ones, can sell for lots of money - like some wines). The process of trying different tubes is often referred to as "tube rolling". There is a lot of hype about tube rolling, and no guarantee that an expensive tube that sounds good in one preamp will sound good in another - or that a cheap one won't sound as good or better than an expensive one. (Also, don't expect different tubes to sound as different as, say, tube and solid state.)

While a tube preamp is a good way to "get into tubes", don't expect a tube preamp to sound as distinctive as a tube power amp. The differences are usually more subtle.

[tweed]

Keith

Thanks for bringing up this topic and conversation. It is one that interests me and I beleive many others. Emo bringing some tube equipment on line will gather lots of attention imho.

[ludi]

Keith,

Thanks for writing about the sound, but I guess listening would be even better. Maybe it is possible to add some listening examples to this thread, just to hear the difference between the two? I know it doesn't make sense to put the sound of e.g. the XPA-2 in an example, but some tube based music compare to neutral music would definitely help. I hope this can help me to understand the descriptions about the differences in sounds.

[KeithL]

HOW TUBE POWER AMPS SOUND

Tube power amps tend to sound quite different from solid state power amps - for several reasons.

The biggest single reason is: output transformers. Tubes are designed to operate at high voltages and low currents. Since modern speakers almost universally operate at low voltages and high currents, a transformer is required to match their operating impedances. (There are some very unusual designs that avoid this, but they make up a small fraction of a percent of the total.)

Mostly because of the requirement for output transformers, virtually all tube power amplifiers have a very high output impedance - which equates to a low damping factor. [Most modern solid state amplifiers have a damping factor well over 100, with over 500 being quite common; the damping factor on tube amps ranges between about 1 and 20.] Without going into technical details, damping factor is the ability of the amplifier to "control" the speaker - and is most noticeable with bass (with the woofer). Most modern speakers are designed in anticipation of being driven by the high damping factor of modern solid state amplifiers. If you connect a vintage speaker (intended to be driven by a tube amp) to a modern amplifier, it may sound slightly lacking in bass - because the amplifier is "overcontrolling" the speaker. If you connect a tube amplifier to a modern speaker that isn't especially designed to work well with tube amplifiers, the bass will often sound "loose" or "boomy" because the amplifier isn't providing the speaker with the control it requires to sound good. Because this varies,  different speakers sound very different when connected to different tube amplifiers, and when connected to tube and solid state amplifiers. This high output impedance of tube amps also makes it more likely that the overall sound will be affected by the differences in speaker cables.

Some tube amplifiers offer a "feedback" or "damping" switch that allows you to choose different damping factors (everything else being equal, increasing feedback increases damping, so changing one changes the other). Changing this setting will make a tube amplifier sound different, and the amount and type of difference will vary with different speakers. Most tube power amplifiers also offer different output taps intended to drive speakers with different rated impedances; but selecting a different tap can also change the sound of the speaker (connecting an 8 ohm speaker to the 4 ohm tap will usually make the bass more solid; especially if the speaker actually has an impedance that dips below 8 ohms).

Some tube amplifiers use triode output tubes, while others use pentodes - or "beam tetrodes" (pentodes have extra control grids). Triode amplifiers tend to have more distortion, and sound "more tubey", while pentodes tend to sound cleaner and more like solid state. (Some tube lovers say that the distortion produced by triodes, while there is more of it, is less unpleasant - or "more euphonic".) Most modern tube amplifiers are "push-pull", which means that they use pairs of output tubes, wired such that some of the distortion produced by the two tubes cancels out. Single ended amplifiers use one tube, but, you guessed it... some tube lovers insist that the higher distortion of the single tube is balanced out by some "magical something" in the way they sound. SET ("single ended triode") amplifiers offer the most extreme combination of a single triode not operating push-pull, and typically have low power and high distortion, but some true tube aficionados insist they sound the best. (Because of the lack of "balance", SET amplifiers also require disproportionately large and expensive output transformers).

As I mentioned before, most tube power amps have a monotonic distortion curve - their distortion increases gradually as you turn them up. This both makes them seem more powerful than an equally powerful solid state amp, and can sometimes make music seem "more dynamic sounding" when played on a tube amp. Since they clip gradually, tube power amps tend to be more forgiving if you overload them (they sound gradually worse rather than getting nasty sounding all at once after you cross an imaginary line in terms of loudness).

Some tube amplifiers have a measurably rolled-off low end and/or high end - but many have a respectably flat frequency response. For some less well understood reason, even tube amplifiers that measure relatively flat still tend to have a softer or "blurrier" sounding high end (imagine the audio equivalent of a "soft focus" filter). To some people, and with some music, this sounds pleasant. (Some tube lovers say, with some justification, that "a tube amp will never sound strident or annoying".)

Many agree that a tube power amplifier is a good match with speakers that are slightly "forward" or "harsh", and not such a good match for speakers that are already "laid back" or "dull" sounding. Of course, a low powered tube amplifier is a good match for high-efficiency speakers. (Many tube lovers match low-power tube amps with speakers like Klipsch or Altec Lansing.....)

[Golden Ear]

Tube equipment sound "euphonic" to me.

[mshump]

Keith
Thanks for all the tube info !! This is great ! I for one have an interest but unfortunately living in the middle of nowhere its hard to demo items like tube amps etc. I had an idea, a couple years ago Musical Fidelity brought out the tube buffer and it sold like hot cakes back then, I read a lot of impressions and they were greatly varied most likely as you discussed earlier with it being a complete different sound. Maybe this would be a good starting point for Bob Carver and Emotiva. A simple buffer would be a low cost way for people to check out the sound at a relatively low price.