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Valve amplifiers

Discussion in 'Electronic Basics' started by esox, Apr 1, 2005.

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  1. esox

    esox Guest

    Guitar question.
    It is said that a 30w valve amplifier is very loud compared to a
    transistor amp. I've heard that 30w valve puts out more than 100w
    Why do they sound so loud?
    I had thought it might be that they are often class A.
    Any ideas?
  2. Guest

    Is it that the distortion is more 'graceful' so you just push it
  3. phaeton

    phaeton Guest

    First off, careful with this question. I've asked it several times
    (not in this ng, but other places where electron-heads hang out) and
    i've gotten a lot of response to the effect of "tube amps louder?
    that's b.s.- watts are watts".

    While "watts are watts" is definately true, my best scientific guess is
    that tube amps have a much broader and more powerful frequency response
    in the midrange, which means they put out more of the waveforms that
    the human ear can pick up best. SS amps can put out the same power
    (watts) but the frequencies will always be different, some of which are
    in the frequencies that the human ear can't hear so well, some more of
    which might be "wasted" in freqs that we can't hear at all (above 20khz
    or below 20hz).

    There is also something like an empathetic vibration amongst harmonics
    that tube amps are better at creating- i.e. the whole even-order /
    odd-order harmonics difference. SS amps tend to create more odd-order
    harmonics that clash and fight with each other, so some of the power is
    affected that way before it even gets to the speaker.

    (I don't have any references to data or any better explanation to hand
    out, so it is very possible that someone may come along and correct

    I don't know about the 30w Tube == 100w Transistor comparison (this is
    like saying 1 Mhz on a Mac == 4 Mhz on a PC... too much other things to

    But i will say that my 5W Reverend Goblin (All-tube) will completely
    blow away my 45W Peavey Pacer (All Solid-State). Yeah we're talking
    different qualities of amplifier and different price points, but the
    proof is still in the puddin' :-D

    If there are any non-believers, i usually suggest them to go into a
    music store, and ask one of the sales d00ds to plug into a 30W or 60W
    Peavey Classic or Fender Blues Deville with the eq set flat. Let the
    non-believer twist the gain and volume knobs around. Then have them go
    to a Solid State amp of the same wattage and repeat. Another good
    comparison is a 10W Champ vs. just about any SS amplifier on the floor
    under $300.

    Nobody's ever done it tho... or at least has told me afterwards..
  4. If you add a preamp stage which compresses the
    signal, a simple cmos unbuffered logic gate, or
    some other way to add soft clipping to the solid
    state amp you will find that they sound equally loud.

    Solid state amps use most of the available headroom
    for the occasional high volume peaks in a signal so it
    has to be run at a much lower total power than a valve
    amp which you can drive very hard whithout blowing
    the speakers or sounding really bad.

    Most modern music use compressors in the mixing
    process, to allow for a loud volume without letting
    really high peaks of voltage through, and that is a
    similar effect as a valve amp creates.

    Electric guitars sound really bad if used without any
    soft clipping at all, it sounds like plink-plonk.

    So electric guitars are always used with either effects
    boxes which add the soft clipping, or with valve amps
    which affect the signal in the same way.

    By the way, commercials in tv often use harder
    compression than usual program sound, so they
    can create a higher subjective sound volume without
    it looking like higher volume on a VU-meter in
    the transmitter control.

    That is why commercials often sound louder than
    other program material where the sound technicians
    care more about the sound quality.

    The peaks are just as high as the peaks in the
    normal programs, but the compressed sound
    sounds a lot higher.
  5. phaeton

    phaeton Guest

    Well yeah, then there's compression- natural (tube) or otherwise
    (compressor/limiter), and that plays a big part too... gently clipping
    the peaks off the louder stuff so you can bring the softer stuff up...

    Sometimes i find modern music mixes, where everything is squashed to be
    somewhat fatiguing to the ear... but that's another subject for another
    rainy day ;)
  6. Jamie

    Jamie Guest

    no, they are just basic Push Pull types into a transformer.
    the transformer tends to suppress some of the harmonics that
    are created from all those over driven jammers.

    Ha,. Valve Amps. who ever thought of that one!~
  7. Ever heard a guitarist telling that a real guitar should not need to be
    amplified... Electric guitars are hardly instruments on their own. The
    amplifier can be considered a part of the instrument. They deliberately
    color the sound. Last Thursday I heard a gitarist playing severel guitars
    using several amplifiers. No doubt the Fender sounds best. Guitar amplifiers
    has been tube amps only for some time as solid states tend to blow the
    speakers. They did not sound either. A lot of guitarists still want to use
    only tube amps. Usually this amps are class AB. The secret most of the time
    is in the transformers. Along with the tubes they tend to smoothen high
    peaks without giving the sharp scratching sound some older solid state amps

    Another point are the Watts. No doubt a Watt is a Watt but is everything
    that's named a Watt really a Watt? Most tube amps grow in a time
    exaggeration did not go that far. Solid state amps tend to be overrated much
    more. Ever saw a 2x10W stereo amp powered bij a 12V/1A wallwart. (BTW this
    was not a guitar amp.) These days solid state amps can be made much better
    but even then some people still hear the difference between a tube - and a
    solid state amp.

    Then the loudness you hear is hardly to be measured in Watts. If you double
    the Watts you will hear only little more loudness. Adding all together it's
    not strange some say a 30W tube amp sounds louder then a 100W solid state.

    petrus bitbyter
  8. Bob Eldred

    Bob Eldred Guest

    You need to measure the power to make a statement like that. You can't go by
    the rated power in the sales lit. or on the name plates. Secondly the signal
    sources have to be exactly the same and not be in distortion which alters
    the harmonics. Sounds may sound louder or softer depending on their
    harmonic character. Thirdly the speakers they play into have to be exactly
    the same. Speaker efficiencies vary greatly. Set up two systems that way
    and actually measure the power to the speakers in each and adjust the gains
    until the powers are exactly the same, measured, then tell us which one is
    louder. Assuming you do not drive into distortion on either I doubt you
    could tell a difference. Do it and let us know.
  9. Guest

  10. *One* potential reason (of many) is dynamic headroom. Most amps are
    rated at steady state average power. This is what heats the amp up and
    forms its fundamental power limit. In some cases tube/valve amplifiers
    have power rails that stay up for a lot longer then transister amps, so
    that the average transient power can be much higher (say for 20ms). This
    is because for a given physical size of power supply filter capaciter
    (size=CV), the higher voltage of a valve amp allows more energy storage,
    by C.V^2.

    A guitar signal is quite high for the inital transient, than decays
    quite rapidly to a steady state value, before finally decaying to zero.
    Therefore, if the amp is set to not distort on the initial string pick,
    the mid time signal will be have to be set lower for an amp with no
    dynamic headroom.

    An other more obvious reason is speaker sensitivity. I use a Fender twin
    reverb combo. Sure, its a valve amp, but I have no doubt the that the
    main reason its way louder then even other valve amps is simply because
    the speakers simple give more output for a given input. Sensitivities of
    speakers can vary tremendously, e.g say, 90 dbspl/1W/M to 105
    dbspl/1W/1M. i.e. equivalent to a factor of at over 5 times.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  11. Pardon!!!

    The fender twang, for the most part is all twang. Suitable only for

    Completely untrue. What drugs are you on? Sure, tube amps don't put DC
    on the speaker if they fail like a transistor one does, but the likely
    hood of a transistor amp killing speakers, today, is very low. In part,
    because the decent ones have protection.

    Guitar amplifiers are made with tubes simply because people want to use
    tube amps. It certainly has nothing whatsoever due to the dubious
    probability of taking out speakers.
    Nonsense. There isn't *one* secret. There are a number of factors that
    go into the tube sound. For example, the higher output impedance. e.go.
    a few ohms verses milliohms. This can be very significant to frequency
    response as the speaker typically varies over a range of 100 ohms down
    to a few ohms.
    This is a bit vague aint it. A transistor amp input stage (+/-15V) will
    clip on its input for initial transients if its input has a gain of more
    then about 20 or so. That is, a good humbucker can put out around 1V pk.
    A valve amp input stage sits on 300V-400V, so it can handle way more.
    So, the dynamic range of the input stages are much better. This means
    that the signal might not clip until the output stage for a valve amp.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  12. The valves sound louder than transistor claim is present even when both
    signals are totally distorted, i.e. constant volume, so compression cant
    be the explanation.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  13. Oh don't get offended, but this is completely incorrect. By
    and large, the frequency response of transistor and tube amps are the
    same if the load is a resister. They usually cover the mid range, when
    tone controls are set "flat" the same within less then 1 db in this
    case. There is an effect due to output impedance, but this makes the
    tube frequency respose technically worse, not better.
    Again, this is all complete nonsense. I don't know of any other way of
    putting this to soften the blow to your ego. This is like me giving play
    tactics on American football.
    Non of this is relevant. Even when set clean, a tube amp is often
    claimed to sound louder.
    Yes. The dynamic range. See my other post.
    These are combos, therefore the speaker sensitivities need to be
    considered. Valve amp combos cost more, so they can use more efficient
    (sound out/watts in), but pricier (better) speakers, and still sell
    within market constraints.

    One needs to compare apples with apples.
    Again, most solid state combo amps use crap speakers. Its a cost issue
    that isn't so relevent in valve amps.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  14. Bob Masta

    Bob Masta Guest

    This might be relevant:
    Many years ago a manufacturer of high-power solid state
    stereo amps ran an interesting experiment. They got
    together an assortment of solid state power amps rated from about
    10 watts to 200 watts, and rigged them so subjects could
    adjust the level without seeing the amp. They asked each
    subject to adjust a test amp until it was "loud". Then
    they measured the actual output power. It turned out
    that "loud" levels correlated more with distortion than
    actual watts: A 10 watt amp putting out max power
    was regarded as loud, but a 200 watt amp putting
    out a clean 100 watts wasn't. Something to think about.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  15. Well, er.. may be. Did you hear the others?
    Sure. But I was talking about the first solid state amps. Some did blew
    speakers particularly the cheap ones.
    The sound of a tube amps, all tube amps but the transformerless ones,
    largely depends on the output transformers. This even holds for the so
    called HiFi tube amps that should not have a sound of their own. That is not
    to say there are no other factors. There are a lot. For instance, some
    freaks claim to hear the difference between two (sets of) the same type of
    tubes but from different manufacturers. But design and component choice can
    make a lot of difference for normal ears too.

  16. You mean the ones who made millions of dollars playing the guitar and
    have a wall covered with gold records? How dare they!

    BTW, the term is Country, not hillbilly.
  17. John - kd5yi

    John - kd5yi Guest

  18. esox

    esox Guest

    Glad I posted this on basics. Hate to see it get too technical :)
  19. That was a way, way, long time ago...Like 25 years.
    Just cant agree on this one. Care to back this up with some experimental

    Sure, transformers might well make a bit of a difference, but there are
    other much more significant effects that even from a technical point are
    quite measurable. To wit, dynamic output power, the input stage not
    clipping, the frequency variations that come from the several ohm output
    impedance interacting with the speaker etc.
    Rubbish. Competently designed valve *hi-amps* that say, have 0.01% Thd,
    flat response etc sound exactly the same as Competently designed
    transistor amps with similar specs. Period.

    The sound differences between say, guitar tube amps and guitar
    transistor amps are all identifiable with measurements that actual say
    they *should* sound different.
    Mismatched tubes may well put the transformer core into saturation with
    smaller signals.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  20. Barry Jones

    Barry Jones Guest

    I noticed the same sort of thing in tube vs. solid state stereo amps or
    receivers. Since they drove the same speakers, quality of speakers was
    not an issue.

    I'd be interested to see how the companies defined their maximum output

    You can drive the amp until there is, say 1% harmonic distortion, and
    call that the max wattage. You can drive the amp until there is 5% or
    10% distortion, or more, and define that as your max wattage. It may not
    be usable wattage, but it sure looks good on the label.

    Since tube (valve) amps are mostly older models, they may have been more
    inclined to rate their products more conservatively.
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