Tube amps have a signature sound

Chris, its on-topic as far as a signature sound is concerned, on account of the fact that tube amps use far less feedback or maybe none at all compared to transistors. I am referring to global or loop feedback.

Local feedback can refer to loop feedback around a single stage, which can still be problematic, or it can refer to degenerative feedback, which does not involve looping around a gain stage and so does not cause trouble.

The ills of loop feedback have to do with a phenomena of all amplifiers called propagation delay. This is the time it takes for a signal to propagate from the input to the output of an amplifier or from the input of a gain stage to the output. The delay is a constant for a given amp and does not change with frequency. From this it might be easier to understand that a loop feedback signal will never arrive back to the input in time to correct the signal that it is supposed to.

As frequency increases, so do problems caused by the lateness of the feedback signal. Eventually this can cause the amplifier to oscillate, so wide bandwidth amplifiers usually have a mechanism to reduce feedback above a certain frequency where oscillation might be possible.

Anyway, negative feedback is a *destabilizing* factor in an amplifier, but will improve overall distortion and sometimes increase bandwidth, at a price: it will, while decreasing most distortions, actually *increase* certain odd ordered harmonics, not much (actually we are talking hundredths of a percent here), but enough so that the overall effect is as MrT describes above as a perception of brightness. You might get with it more detail (as getting rid of distortion reveals detail underneath), but the amplifier may be painful to listen to.

My own opinion is that feedback has to be avoided if you are to have an amplifier that will lack loudness/harshness cues. You still want to get detail, so you still have to reduce distortion- you do this by using linear amplification devices and techniques, so distortion creation is minimized. A couple of examples are triodes and class A operation. Of course, I think a major contributor is the output transformer :)

Ralph, I have read somewhere that in fact negative feedback could improve an amplifier's behaviour. Is it true that there are two sorts of negative feedback: global feedback and local feedback and that global feedback is the bad one? I know this issue is a bit off topic but could you elaborate a bit? Thank you in advance.

Chris

MrT, I interpreted your comments correctly. I want you to understand that I was not contradicting you either. What I was pointing out is that what you were reporting in your post has an underlying design issue, and what can be done about it.

IOW your perception of a frequency response issue is in fact also related to detail in many amplifiers. Here is your comment:

i find many in-production tube amps unbalanced in frequency response and overly detailed. there is often too much treble energy. i find this is the case with solid state amps as well.

I was commenting to the design issues that cause 'brightness' and 'overly detailed' to be related. It is negative feedback.

As robertwolfee says, trust your ears. I have tube and SS integrateds and I listen to the tube one. It is more expensive, a Viva Solista, but it is streets ahead of the Karan K180. Done well, which the Solista does, there is no midrange warmth. The 845 SET is lightening fast, clean, uncoloured and lacks the grain and fatigue of SS. The only downside, is soundstage width.
I suspect if you did an experiment and gave 100 HiFiers a similarly priced SS and tube amp, most would listen to the tube one

hi ralph:

i think you have misinterpreted my statements. detail and frequency response are two different variables.

i said that i perceive many solid state and tube amps and preamps which are in current production to be overly resolving in their presentation as well as having an unbalanced frequency response.

at some point resolution passes a threshold which leads to unpleasant listening.

an unbalanced frequency response is also unfriendly to the ear.

most tube and solid state amps and preamps are unpleasant sounding, subjectively speaking, of course.

Mrtennis, it is possible to get more detail without an excess of treble energy. This is where understanding the rules of human hearing comes in.

The traditional way to get more detail is by reducing distortion. Distortion 'masks' detail ('masking' is a quality of the human ear; one of those rules...). Usually this is done by adding negative loop feedback. While this reduces distortion overall (and thus increases detail), negative feedback will also augment certain odd-ordered harmonics slightly, but enough that our ears detect the augmentation has hardness or brightness (another rule of human hearing: we use odd-ordered harmonics to detect loudness and we are **very** sensitive to them, even in amounts of only hundredths of a percent).

Negative feedback frequently tends to compress dynamic contrasts also. Incidentally an amplifier that employs lots of feedback might measure very flat, but is very likely to sound bright.

So the way to get more detail (and impact) without brightness is to reduce distortion without using negative feedback as a crutch. This results in a detailed amplifier that is also at the same time very relaxed and lacking artificial loudness cues of the type you mention.

IOW: you can have your cake and eat it too.

all products are imperfect. thus, they have some consistent characteristic which can be identified after some duration of audition. if products sound different i, it may not be meaningful to generalize about coloration attributable to tube designs.

i find many in-production tube amps unbalanced in frequency response and overly detailed. there is often too much treble energy. i find this is the case with solid state amps as well. the trend in the design of electronic components is to provide more and more detail, less noise and hence a more unflattering presentation of less-than-ideally recorded music. this is unfortunate, but unless one wants to purchase components, especially tube gear from the 80's and 90's, one may ride the carousel of dissatisfaction and frustration.

If you haven't heard a tube amp with good high end then you haven't heard a good tube amp. There are a few that do it all very well, the Stereophile class A rated Music Reference for example.

And yes, I would agree to the original premiss there that SOME tube amps have a signature sound. When I pull my RM9 out of the system and move to my Quicksilvers I do it to hear their character. Both of these designers use tubes for good reason and with good results.

Bigkidz- If you bi-amp correctly, you'll never go back. For instance, read this: (http://www.avguide.com/products/product-1672/) Click on the review. I'd been using a Dahlquist DQLP-1(slightly modded over the years) since 1981 with great results. The time-alignment that the TacT provided took everything to a whole new level, and still proved as transparent as the Placette Passive Linestage I'd used last with the Dahlquist.

Bigkidz, I've biamped with SS on bottom and tubes on top. The sound was nice, but in the end, it was more of a pain than it was worth... four PCs instead of two, two pairs of ICs instead of one, extra space, extra heat, clutter. I was glad to dismantle it. It was overkill with little sonic benefit. -Mark

Kurt Strain - love your reply and was hanging on to every word. Had to re-read your replies a couple of times before I finally got it.

Another factor worth mentioning is that the input impedance (Zin) of a typical valve power amplifier is usually about 100kOhm. A typical SS power amp is usually about 20kOhm.

This means that the valve amp will require less current to tickle the valve into action. Depending on the output impedance (Zout) of your preamp (the ratio of preamp ZOut / poweramp Zin determines current flow) - you will find that power amps with lower Zin are more resolving of low level signals. Which may be another explanation why I have observed that valve amplifiers seem to resolve more detail and create a better soundstage.

And that's why tube amps seem to play more loudly than SS of the same power rating(without giving the listener a headache)- soft clipping. You're preaching to the choir. One day(if I win the Lotto) perhaps I'll be able to afford to go OTL. Of course my listening room gets quite warm in the summer with no more tubes than I have in the system now. ALAS- champagne taste and a beer budget!!

Rodman99999, the clipping of an amplifier does produce a square wave, and those 'corners' are where the odd harmonics reside.

If you compare a tube amp to a transistor amplifier when both are clipping, the much harder clip of the transistor amplifier is visible on any oscilloscope and the obviously higher quantity of odd-ordered harmonics is easy seen. This is why transistor amplifiers have a harsh overload character and also why most guitar players prefer the smooth overload of tube amplifiers.

Bigkidz- I've been doing that for the past 18 years(and bi-amping in general since 1981). Need any tips?

Anyone bi-amp with tubes on top and SS on the bottom?

Which is why I run a nice sounding tube preamp with solid state monoblock amps in my rig,
kinda gives me a little of the best of both worlds.

Excellent point Rodman9999. And I do know the difference between Zildjian and Sabians or a Paste. Or when the drum stick strikes the skin of the snare drum head in the middle or partial on the rim simultaneously.

That's funny- On my system I can discern the silk of Zildjian cymbals from the brassiness of Sabians(for instance). My guess would be that you've never heard a properly tweeked tube system(could have been the cables, the tubes, the source(who knows?). How I wish I could be happy with a SS system. SO MUCH cheaper and easier to live with!!

In defense of solid state, because somebody has to, I have yet to hear tubes recreate shimmering cymbals to my satisfaction. Also, I prefer the more stable, laid back presentation of good SS. The bass I can deal with. So, while solid state is not ideal, it has been the best compromise for myself. Admittedly, my experience with tubes has been limited and my speakers have always been relatively low impedance.

That's funny: I always thought of the top and bottom of the waveform being flat as DC(simplest terms), as in while a SS amplifier is clipping. Ya learn something new every day

Rodman99999, its OK. Square waves are by definition made up exclusively of odd-ordered harmonics of the fundamental waveform (that's why they can sound so obnoxious). Maybe I should have mentioned that earlier.

My contention here would be that the square wave, being an irritant and obnoxious to the listener, might be PERCEIVED as louder. Same reason most people would get "listener fatigue" sitting in front of a system with a lot of IM distortion. Ah- OK: "loudness cue", not actual loudness?(just re-read your post) Not that the sine wave and square wave would deflect an SPL meter to different levels at the same power, but that the square wave would be perceived to be louder? Are we saying the same thing here? I'm REALLY not intentionally being obtuse....Honest!

Rodman99999, it is easy enough to demonstrate that in fact odd-ordered harmonics are indeed what the human ear looks for as a loudness cue. Its an easy test.

Get a sine/squarewave generator, an amp, a speaker and a VU meter. Run the sine through the amp and speaker and set the level so the VU meter reads 0VU (the meter will be across the amp terminals, this is not a loud test but it can be if you want). Now run a squarewave, and set its level such that is sounds to be at about the same level as the sine wave. You will find that the equivalent level is in the neighborhood of -20 to -24 db to get the same effect of volume. That's at least 1/100th the level of the sine wave!

Try it!

Different tubes have a basic signature sound, EL34, 84, KT 88, 6550, 6SN7, etc. You can characterize the sound of tubes versus SS but there are some manufacturers who have designed tube components to be faster, more dynamic, etc. The 6H tube comes to mind for me. That being said, go hear an old Eico with the EL84 tube and hear what a fluid mid-range really sounds like. I recently heard a modified Dynaco ST-70 and it was wonderful sounding. No SS amp that I have ever heard can do what these tube amps can do. I have an old Lafayette KY-550 and it is an outstanding sound amp in stock form. The closest I have heard to a tube amp that is not a tube amp is the Gilmore stereo power amp. Not as 3D sounding but very musical in the mids.

Happy Listening.

Yes, tube amps sound different from SS amps Chris. The "Signature Sound" of tube amps to me is palpability, or the fuzz on the peach effect. Yes, SS is quieter and has better bass definition, and I've heard smooth SS, but I've never heard SS have the "fuzz on the peach" palbability of tubes.

Cheers,
John

I think that the sound is more dependant on the tube character that goes into them. I think tube amps tend to have a signature character rather than sound and that is what has been described here. Characteristics meaning lifelike mids, soundatsge, imaging and soft on the extremes.

Odd ordered harmonics have absolutely nothing to do with loudness or SPLs.( http://www.thewhippinpost.co.uk/glossary-H-M.htm) (http://www.hometheaterhifi.com/primers/the-primers/negative-feedback.html) They WILL give you a massive headache however. Both of the above sites contain definitions of odd-order harmonics. The only correlation between them and loudness is that overdriving a solid state amp produces much more, and overdriving a speaker system can cause a lot of intermodulation and/or saturation of the crossover. One of the reasons amps sound more accurate now days is that the components(capacitors, resistors, even wire) used in manufacture have been vastly improved upon. Unfortunatly the TUBE manufacturers have not been keeping up. The tubes made in the 40's through the 60's are still the most lucid/transparent/accurate on the whole. As I stated earlier: Read what the experts that use LIVE MUSIC as a standard(both amplified and acoustic) have to say on the issue. Become very familiar with live music yourself, then judge the accuracy/staging/imaging/sound pressure levels of your system accordingly. Of course: everyone's goal isn't the same. Some folks are happy to have their eyes tickled. If everyone had the same tastes; this would be a very boring world. If I can't close my eyes and pretend I'm at the original recording venue(NOT the band playing in MY room, and not all recordings contain enough encoded info to allow this), it's hard for me to even tap my foot.

I don't know, both can sound terrific and it all has to do with the implementation.

I guess it's in the eye of the beholder. I would argue that modern high quality tube amps don't sound colored or have a "signature" compared with solid state which sounds less natural overall.

Solid state tendencies:

-emphasize the leading edge or transient at the expense of decay

-overly etched sound and images that doesn't resemble anything heard in real life.

-a congested or clogged sound (when compared to the best tube amplifiers)

-an inability to resolve the space between the performers, making it sound more like instruments and voices in a black hole

-bass that extends down to DC but sounds overdamped and less natural

Now, all that said, there are some fabulous sounding solid state amps that minimize, to a great extent, all of these shortcomings, but they don't totally eliminate them when compared to the best tube amps.

In fairness, I will also admit that tubes have a couple of weaknesses of there own, but as Atmasphere has pointed out, they are less of a problem because they don't contradict the laws of human hearing.

The longer I've lived with tubes, the more I've tried to purchase or modify tube components to eliminate that tubbey midrange bulge that sometimes comes at the cost of sluggish dynamics and mediocre bass control. Somewhat rare is the tube component that sounds clear, neutral, and dynamic, while being faithful to the seductive sound of tubes.

Seasoned, a slightly over-ripe presence region in the VK75SE is not attributable to tubes, but rather to BAT's choice of PIO coupling caps. A good teflon cap in this amp will enhance clarity & neutrality without sacrificing warmth.

If there is a 'signature sound' it is the low levels of odd-ordered harmonic distortion which our ears are evolved/created to detect. Odd-ordered harmonics are how the ear detects loudness. Tubes make far less of this than transistors. Transistors don't make much either, but the hundredths of a percent that they *do* make is a demonstration of how sensitive our ears are to this type of distortion.

By contrast our ears do not care so much about even-ordered harmonics, but a properly set up push-pull tube amp is not going to make a lot of those either. So if the amplifier is set up right, and other important design considerations are met, a tube amplifier will sound more natural to our ears than a transistor amplifier will.

So IMO, the 'signature sound' is music.

There are technical reasons why tubes sound different from transistors, usually. Why there is so much controversy surrounding it is a mystery to me when there is plenty of objective reasoning to show they are different animals.

First, the tube is a higher impedance, higher voltage, lower current device than the transistor in almost all cases. This has to alter the design topology and interface between components when dealing with those differences alone.

Second, the triode is a unique device not duplicated in the transistor world in terms of its characteristic curves. There is a tiny but mostly unused and ignored portion of the curve of a FET (JFET, MOSFET, it doesn't matter) called the "triode" region. This is the only place it mimmics the behavior of a triode, and is basically so small an area as to be unusable. The FET is used in the "saturation" or "constant current" region, and mimmics more closely the pentode. A BJT is a current amplifying device that is also different than these others.

The triode has curves that have the following properties: nearly infinite DC impedance in common cathode configuration except for the biasing resistance, and current increases with increased plate voltage over the entire range of operation. Pentodes, like FETs, don't act that way because they go into constant current for increased plate (drain) voltage. In both cases I'm talking about holding the input voltage constant when raising the plate (drain) voltages.

This triode characteristic curve does an interesting service in a typical common cathode amplifer stage: as plate current increases from increased input voltage the plate voltage decreases as any inverting amp stage should, but with the decreasing plate voltage the tube wants to counter that increased plate current. This is local negative feedback built in without even trying.

So the triode typically has lower gain and lower distortion than a pentode or FET that does not have this local negative feedback working on its own.

You can make this triode amp sound more like a transistor amp by applying the same global negative feedback techniques that most of the transistor amps use, and you might like that. But there are limitations: triodes are lower gain and lower bandwidth usually so less NFB can be applied for similar overall gain. Thus you are left with some residual triode sound even if you try to squash its signature distortion.

It's not that there's a frequency response rolloff that accentuates the midrange. That midrange emphasis is more likely a feature of the distortion spectrum of the devices in the midrange compared to the extremes from two likely sources: A loose midbass with lowered NFB and poor PS regulation can produce harmonics into the midrange that decreases with increasing frequency. And then in the highs there is again a decrease in overall NFB which changes the uniformity of this distortion spectrum. The result is a frequency dependent distortion of unique triode-produced distortions, be it considered good or bad.

And while some people claim that distortions are not audible when "linear enough", also realize that in a bottle of wine that contains 14% alcohol and a lot of other complex chemicals, the whole bottle can be ruined by 5 parts per BILLION of the chemical that makes it taste "corked".

There are three kinds of distortions: audibly pleasant, audibly unpleasant, and inaudible. How much is audible of what kind of distortion is very difficult to find out through experimentation since it's almost impossible to alter just one kind of distortion at a time.

What is considered "most accurate" is still a judgment call. Many people say the triode amp sounds "most accurate" when compared overall to live, in most implementations, and I still agree with that. Why? I don't know and I can tell no one else has that down to a solid science yet.

Kurt

The most consistent sonic tube signature is not the sluggish droopy ill defined sound of the golden era of "hi fi"!
Instead I am convinced it is a much more pronounced 3D soundstage. That is if you are talking of the currently produced tube amps. The degree of upper end sparkle and controlled bass, is very variable. That is clearly audible however there is in addition a very important psycho-acoutical sound.
It is referred to as a distortion, but you can't pick it out it is sort of invisible, if you will. I think is 2nd order distortion. Again I can not describe it but it is there and most people really like it. I can say what it is not.It is NOT poorly defined, fuzzy, rolled off, sound or anything of the sort. It is a highly desirable harmonic phenomena.
If you want to hear what I think people refer to as tubey, then you might try to find a tube amp from the "golden era of Hi Fi" i.e. the 50s until the mid 60s". That would be the extreme of the misapprehension of what a typical modern tube amp sound. It is by all means coming from a tubed amp you are thinking of what you heard 40+ years ago. And for all of you who think I don't know that current tube amps vary widely from directley heated triodes to push pull to SETs and they all sound different you are incorrect. However if you have the experience of listening to a current tube amp of any stripe and say that the usual perception/recollection of tubey, then surely you jest.
I happen to enjoy that Hi Fi sound when feeling nostolgic, which is only occcasionally. If you really want to hear the old tubey sound IMHO, Don't forget you will probably hear it best with the same era speakers. For some odd reason I find the source doesn't seem to have the impact it does on modern systems, but clearly a "record player" is appropriate.
Most of these amps are integrated but if component the pre will already have a "phono" stage input, MM BTW. The only other choices were a tuner and reel to reel for the truly insane. I attribute my ability using curse to the Reel to Reel we owned. My father would become increasing frustrated until his rather expansive cursing vocabulary spewed forth. I recall it was about a 50 - 50 chance that it would get tangled up, off track or some other other calamity would happen.
Or I could have simply said just go out and listen to a !@#%%^&* highly regarded, modern tube amp and you will hear what a tube amp sounds like..

What experts have to say has nothing to do with one's decision if you really spent the time to listen to live music.
For example, going to concert, listen to how a live piano and violin play.
The human ears are very sensitive and very adaptive at the same time; if one tells the brain that this is closer to live music, that would be closer to live music.
I do not believe any of the so-called "experts", for example, those "tin-ears, but big money marketing people" would give you, or the poor so called "audiophile" honest answer.
They always recommend the big advertising money sponsor's equipment.
TRUST YOUR OWN EARS !!!!!!!!!!!!!!!!!!

I've been listening to live music as a sound tech/engineer since the late 70's. My experience has paralleled that of the reviewers in Stereophile, The Absolute Sound, FI, and most other "high-end" rags. Tubed equipment just sounds more like live music than SS. Of course there are tubes that impart colorations(microphonics, sugar coating/glaze, tubbiness, British sound, etc.), and tubes that just convey the truth(usually NOS and German or American). That's why so many of us(tube/musical truth lovers) spend so much time "tasting" so many different tubes. I've got a VK-D5 CD player and a pair of Cary SLM-100s. I've lost count of the tubes tested/rejected before settling on six Siemens CCa's(from the 60's) for the BAT, and the TungSol round plate VT-231s(40's), Sylvania 6SN7W tall bottles(40's), and Winged 'C' 6550's(latest iteration) in my Carys. I'm bi-amping with SS for the bottom because it's just easier to get good/fast bass with solid state. I'm using planar speakers for mains, and a subwoofer sytem has to be fast to seamlessly blend with them. You and I will probably have started a major controversy with your question and my response. Don't be confused by all the opinions you'll get in here. Read what the experts have to say(those not swayed by advertising dollars and that are familiar with live music), you'll find that the highest rated equipment is invariably tubed and SS is usually compared to and judged by how close it gets to that standard. BOY- is THAT statement ever inflammatory!!

Chris,

Glad you have seen the light and welcome aboard. You're right...tube gear does have a signature sound. They have a laid-back reach-out-and-touch palpable presentation that many of us prefer. They are not for everyone, hence the controversy, owning one is a matter of taste. Some like chocolate; some vanilla. Some Ford trucks; some Chevy. The wonderful thing is that we have a choice. I have gone from SS to tubes; back to SS, then tubes again. Finally got off the merry-go-round with a BAT VK75se.

Well the ones that are accurate are critized for sounding like transistor amps. The ones that do sound like older tube gear have a great midrange partly because their hf response dips and let's your ear/brain processor focus more on the mids. At any rate, humans are more sensitive to the midrange so that having more presence there will seeem like a good and great thing.