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general question about audio amplifiers

Discussion in 'Electronic Basics' started by [email protected], Mar 9, 2005.

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  1. Guest

    Hello,

    A family friend swears by using vacuum tube audio amplifiers, saying
    that although they are less efficient, they produce a "warmer, less
    tiring" sound than the traditional electronic amplifiers do.

    Is this really true?

    Would, for example, the output waveforms be smoother on a vacuum tube
    than they would be on a transistor amplifier?

    Thanks in advance for not flaming me too badly.

    Mike Darrett
    www.darrettenterprises.com
     
  2. Good places to ask this, after reading their FAQs,
    would be rec.audio.tech and rec.audio.opinion .
    This is undoubtedly covered in a FAQ.

    Some people like the distortion of some tube
    based amplifiers. Some imagine they like it.
    The simple fact is that if such sound was all
    that desirable, it would be on CD's and such
    for the benefit of those with low distortion
    audio systems.

    Tube based amps will limit more softly than
    simple implementations of transistor based
    amplifiers. But again, if that characteristic
    was so desirable, it would be effected by
    non-linear shaping circuits in solid-state
    gear. The fact that such gear has not been
    marketed (much, at all?) indicates that it
    is not an important technical feature.

    In fact, most people to whom such gear
    would be marketed would still prefer
    vacuum tube amps, magnetic bracelets,
    and sea salt.
    Only when the amp is underpowered for
    the signal it is being asked to pass.
    You can take my FAQ reading suggestion as a
    not too bad flame, if you like.
     
  3. Tube amps softens the curve form, a soft clipping action, because they
    are not good components. But this is a fault which some people like
    better than a perfect reproduction in a modern transistor amp.

    There is a whole industry based on making transistor amps sound like tube
    amps. And some people build real tube amps after old schematics.
    Guitarists are the main target group for this, but other audio
    enthusiasts also buy tube amps or effect boxes which reproduce a classic
    tube sound.

    google:
    tube screamer effect box schematic

    http://www.geofex.com/Article_Folders/TStech/tsxtech.htm

    A good text about creating tube sound in different ways, simple
    do-it-yourself circuit schematics.
     
  4. John Larkin

    John Larkin Guest

    So solid-state is now "the traditional electronic amplifier", and
    tubes are new? To some people, I guess.
    This is notoriously subjective, like wine tasting. It would be
    interesting to have him do a blind listening comparison and see if he
    can tell the difference. Some tube amps *do* have a lot of distortion,
    and some people do like the resulting sound. Tube amps have bad
    damping factors, so speakers boom more, and some people like that,
    too.

    John
     
  5. Guest

  6. As an amateur guitarist of about 20 years (late starter ;-), I can
    attest to the _fact_ that there is a world of difference between solid
    state and tube. It's mostly a behavior thing IMO. Feedback in a solid
    state amp is a terribly atrocious noise. It tends to seek some magic
    frequency known only to the evil force driving it and having nothing to
    do with the notes currently being played. The victim has no semblance
    of control over the howling and screeching noise that is known as
    solid-state feedback.

    OTOH, a good tube amp can "sustain" any chosen note for an indefinite
    amount of time. The practiced player can have an amazing amount of
    control over the effect. Just listen to an early Van Halen album for an
    example of what's possible with tubes.

    Outside of this, I believe that most audio-phool hype is nothing more
    than another form of snake oil for the modern times. For reproduced
    audio, I have no qualms with solid state equipment. But a guitar should
    only be plugged in to a tube amp, period. ;-)
     
  7. John Larkin

    John Larkin Guest

    But there is some rationality to sea salt.

    John
     
  8. Me too. I have a Casio MG510, a famous guitar you have probably never
    heard of. A stratocaster type body with three analog pickups, one of them
    is a double humbucker pickup.

    The guitars themselves were produced under contract for Casio by Fuji Gen
    Gakki, who also built the Roland and Ibanez MIDI guitars.
    It has a traditional analog output jack like all electric guitars, and a
    midi output like a midi keyboard.

    I cut away a lot of wood from its body to make it lighter, and slimmer.
    Electric guitars weigh too much in my view, or I am simply not well
    trained and strong. It looks better after the slimming. I can use it as a
    keyboard and use a sequenser program in the computer to record in midi,
    or I use a Zoom 505 effectbox and record analog tracks.

    Mechanically it is the best guitar I have ever played, very soft and easy
    action. It is probably taken from the same production line as high
    quality Ibanez guitars.
    I think he uses more than just a tube amp. He uses effect boxes, like the
    tube screamer I wrote about in another message. You can build your own
    effects boxes if you know a little electronics. There are schematics for
    most older commercial effects on the web, geofex.com is a good starting
    point.
    The latest word in the effects world is "guitar modeller". It is an
    effects unit which simulates different guitars, combo cabinets, amps,
    loudspeakers, etc.. So you can sound like you are playing a 1972 Fender
    with a Marshall amp.

    An example:
    http://www.imuso.co.uk/ProductDetail.asp?StockCode=EG00071
     
  9. Cool. I have exactly one guitar (the one I started on), an Ibanez Strat
    copy with a maple fingerboard. It still looks pretty good even after
    more than 20 years. I changed one of the single coils out to a Seymour
    Duncan hum bucker that fit in the pick gaurd without cutting (i.e. looks
    just like the stock single coil) Ah...way less hum. ;-) I've had
    several amps, but I finally found one that I like. It's a Mesa Boogie
    DC-3.
    I kinda gave up on the stomp boxes when I got a decent amp. Even my
    Zoom 505 just didn't sound right. It stole all my head room. I suspect
    that more modern stuff may be better now, however I don't play a whole
    lot anyway so straight in is fine for me.
    Yeah, the amp modeling stuff has been around for a little while, but I
    didn't know about guitar modeling. That's pretty impressive looking for
    the price, I'd like to hear one. I need to go check out what's
    available at Guitar City, I haven't been there in eons. Do you remember
    The Rockman?

    I think I'll stick with my Boogie though, it really does kick butt.
    Worth every penny and then some. It's the freakin' loudest 35W I ever
    heard in my life. My cats agree. ;-)
     

  10. Yes, if we are talking pocket sized units. I wanted one 10-15 years ago,
    when they came out on the market. but never actually got my hands on one.
    I built my own effects for several years instead.

    The best homebuilt unit made the guitar sound like an organ, with
    infinite sustain in its maximum sustain position. I could also set it to
    swell, the tone starts quiet and builds up volume.

    Years later I got a Zoom 9002 pocket multiprocessor, which I liked very
    much. It was trashed by lightning, so I went out and bought the Zoom 505,
    because it was the most common unit, I had read a lot about it, and I got
    a very good price.
     
  11. tempus fugit

    tempus fugit Guest

    Eddie's thing was to mod the Marshall he was using by using a Variac to up
    the tube voltages (or was it down them - can't remember now). Anyway, he
    claims he had to retube once a week!!
    He used very little in the way of effects, but one of his secrets was to use
    a phaser (and MXR I think) turned barely on for a little treble boost. You
    can actually hear the phasing if you listen closely though.
     
  12. I often use a triangle wave from a function generator as input signal to
    test and trim circuits to simulate tube distortion.

    When I adjust a jfet or mosfet stage, or a tube screamer diode clipping
    circuit, I can see on the oscilloscope how the peaks of the triangle wave
    are rounded.

    It sounds better if the positive peaks and the negative peaks are rounded
    differently. That gives a more interesting spectrum of overtones than if
    the soft clipping is symmetrical, which sounds more neutral.
     
  13. Kitchen Man

    Kitchen Man Guest

    There are now available PC sound cards with a vacuum tube final stage.
    While I am nostalgic about vacuum tubes, having worked extensively early
    in my career with tube power supplies and pentode analog computers, I
    don't harbor any great desire to spend the kind of money necessary to
    get tube audio equipment. But, I do like sea salt. :)
     
  14. John Fields

    John Fields Guest

     
  15. James Beck

    James Beck Guest

    Yep, there is more than just NaCl in it.

    Jim
     
  16. That might have been overstated a bit. But I think
    the point is correct that a large fragment of those
    who insist that tube amp distortion is preferable
    attribute tubes with magical properties than can
    never be replicated otherwise, no matter what
    thorough instrumentation might indicate. And
    among that fragment, you will find many with
    magnetic shoe inserts, copper bracelets, or a
    cupboard containing many items with sea salt
    in the ingredient list. The superstitious mind is
    rarely content with isolated obeisances.

    Do you believe that, within the nearly linear output
    range of a tube amp, the output transformer is
    usually going to smooth out the content that a high
    fidelity amplifier would have passed? If that is the
    basis of your contention, then I must point out that
    transistor amplifiers can also act as low pass filters,
    either intentionally (treble control) or not. If your
    contention is not about frequency response, maybe
    your could explain your contradiction.
     
  17. John Fields

    John Fields Guest

    ---
    Superstitious minds also exist among those who prefer "semiconductor
    sound" and I'm sure that, among that fragment, you'll also find many
    with magnetic shoe inserts, copper bracelets, or a cupboard containing
    many items with sea salt in the ingredient list, so I can't see why
    you're singling out those who prefer "the tube sound" as a population
    more likely to be superstitious than another unless it's for the
    purpose of denigrating them because they have preferenes different
    from yours.
    ---
    ---
    There is no contradiction.

    The frequency response of a transformer is determined by using a
    constant voltage, constant impedance source with a sinusioidal output
    to sweep the input of the transformer (the "primary") through a band
    of frequencies while measuring the output voltage from the resistively
    loaded secondary and taking note of the output amplitude variations.

    The transient response, on the other hand, deals with the behavior of
    the transformer when subjected to complex input signals and is
    affected by, among other things, the leakage reactance and
    interwinding capacitance in ways which wouldn't be readily apparent
    when exciting the transformer with a single spectral line. For
    example, do you think that if you had a transformer with a flat
    frequency response from 10Hz to 20kHz at 10 watts and you fed it with,
    say, 100Hz and 8372Hz simultaneously that its output would exactly
    mimic its input? I don't, and I don't believe that if you fed the
    output of that transformer into a loudspeaker side-by-side with an
    identical loudspeaker being fed with the output of a solid-state amp
    with a treble control that the inputs to both loudspeakers could be
    made indentical no matter how the treble control was adjusted.
     
  18. You are mistaken about my preferences. I cringe
    when I hear hard-limited sound and would prefer
    the softer limiting that tube amps can provide.

    My "singling out" is directed not to those who may
    prefer a given type of distortion or limiting, but to
    those who believe only tube amps can deliver that
    performance. I have seen no studies of how tube
    amp preference correlates to superstition, so my
    above statement is based on a small sample and
    may well be unrepresentative.

    Well, prepending 'not' to what I posted can certainly
    be reasonably interpreted as a contradiction.
    For a linear time-invariant system, the transient response
    is perfectly predictable from the frequency response. So
    your distinction is somewhat puzzling in this context.

    As for the properties you attribute to the transient response
    that are not visible in a magnitude versus frequency plot, my
    understanding is that humans are insensitive to the phase
    relationships among components of an audio signal.
    Such fidelity would surpise me.
    I agree with that. But I doubt anybody could
    hear the difference provided that there was no
    wild difference in the phase response of the
    two systems, such as delay in excess of a mS.

    What triggers my skepticism is the suggestion
    that transformer transient response uniformly
    tends to smooth output waveforms. I expect
    that in the case of soft limiting, but I see little
    reason to predict that the uneven phase response
    of a transformer, together with the phase response
    of whatever is done to preceeding stages to get
    the magnitude response straightened out, will act
    to produce smoother outputs.
     
  19. John Larkin

    John Larkin Guest


    A relative-by-marriage used to be head chemist for a big salt mine in
    Louisiana. Every day he'd go to work, analyze some samples, and file a
    report: yep, it's still salt. He got bored, took up selling drugs, and
    now he's a successful and respected mobster, sort of the cajun Tony
    Soprano.

    John
     
  20. John Larkin

    John Larkin Guest


    Oh, don't be bitter.

    John
     
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