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Question about distorting tube amp

Discussion in 'Amps and Cabs [BG]' started by debozkurt, Feb 21, 2008.


  1. Hey fellas,

    I have a Mesa 400+, and was wondering a couple things.

    What's the best way to get the best distorted sound out of this amp without damaging my equipment? I was cranking the power section, but I know this can cause the voice coils in my speaker to melt....Yet I can't get the same type of distortion out of my pre amp section...

    Any thoughts?

    Also, cranking the pre amp section doesnt send these squared off waves straight to the speakers, but to the power section to be amplified as a total signal, so distorting the pre amp section shouldnt have any inherent damaging effects as well, correct?

    Thanks guys, really appreciate it!
     
  2. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Actually, that whole business about distortion causing voice coils to melt is a myth. Think about guitarists, playing with screaming distortion all day every day- their speakers are not melting. Even if somebody thinks they're clever by calling distortion a square wave, it's not actually a pure square wave in most cases, it's usually just "sort of" squared off. And usually people who call it a square wave then insist that square waves are DC, and that feeding a speaker pure DC will melt it. Again, this is not acknowledged as "fact" by most amp or speaker designers. It does get debated endlessly on this forum though.

    Long story short, as long as your cab is rated for a good amount of power, you should be able to crank your Mesa (both preamp and/or power sections, to your taste) without melting anything other than your ears.
     
  3. TrooperFarva

    TrooperFarva

    Nov 25, 2004
    New City, NY
    The 400+ is designed to be clean, for a tube amp. It's hard to get it to break up. You might consider picking up an old Mesa D-180. It had 2 channels, one of which was designed for distortion.
     
  4. and that can, and will happen.

    i've seen some pretty disfigured ears from that kinda stuff.
     
  5. chaosMK

    chaosMK

    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    A good starting point is-

    Master 10
    Bass 1
    Treble 2
    Mids 8-10
    Pre 3-4

    Hope you have a full stack. Though, I have run my amp at power section OD levels through a single (powerhouse) cab and it didnt cause a fire or anything.
     
  6. Well, comparing what most guitarists do to achieve distortion and what I'm talking about is not entirely an accurate comparative example...The distortion that they use is often times preprocessed before it even gets to the power section of the amplifier. In the case of a distortion pedal, the amplitude is boosted until clipping occurs. I am talking about distorting the power section of an all tube amplifier "naturally". Also, back in the earlier days of guitar, when distorting an amplifier was still a new thing, artists were blowing out their speakers because they cranked the power section to achieve speaker distortion.

    Distortion of the power section in such a way can very much so cause damage to your speaker. An amplifier will output AC, and if pushed hard enough, to the point where it can no longer perform normally, it will begin to cut the crest of the wave off at some point...During these brief moments where the wave has effectively flatlined above the realm of headroom, and into distortion, the speaker is pushing out and in, and holding there during the + and - crests of the wave. This builds up heat in the voice coils, and can lead to them failing. This is in an underpowered situation.

    Now, I know that with tube distortion, it is rather different...Instead of a harsh clipping, like the aforementioned, it compresses the wave more.

    So I guess basically I am wondering if anyone can give me a little bit more insight into how the tube distorts the signals received, and if cranking the pre amp section is better than cranking the power section to achieve a "non-harmful" distortion with the amp.

    In hindsight, really, I doubt that I am really overdriving the power section itself, as I don't turn it up past 5 or 6....and do the rest of my adjusting with the channel volume...It only breaks up once my channel volume reaches the same level.

    TrooperFarva, really? I have never had any trouble getting mine to break up when pushed hard enough. If I turn the master to 5 or 6, and then setting the channel volume the same, its some pretty heavy distortion.
     
  7. The tube amp that is really designed to break up is the Traynor yba 200-2. You can adjust it so the pre-amp distorts but not the power tubes and you can set it up so the power tubes distort and not the pre-amp. And then of course you can adjust it so bother pre and power tube distort. At around 200 watts you can get a nice power tube distortion w/o killing anybody.
     
  8. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    There is not a "process" that converts a distorted signal from "dangerous" to "safe". (Aside from turning it down ;) )
    That is how natural distortion occurs. How do you imagine it to be different?
    First, "back in the day" doesn't address the literally tens of thousands of guitarists since then using very high levels of distortion all day, every day- and thus it doesn't have anything to do with your current question. Secondly, you are not aiming for speaker distortion; if you have a cab with suitable power handling, you can crank the power section of your Mesa with no speaker distortion. One problem "back in the day" was that there were no commonly-available speaker cabs that had high power handling- but we've had commonly-available high-power cabs for a couple of decades now.

    You are describing a situation in which a person is using a cab outside its rated abilities. The solution is simple- don't do that. Use an appropriate cab. It is not related to the amount you're distorting the power section of the amp. If you search in this forum on the terms "underpowering" and "overpowering" you will find many many threads in which the amp designers, speaker designers, and engineers in this forum flatly put down these claims about distortion melting speakers as a myth.
    There is no difference in "danger" between distorting the preamp tubes and distorting the power section.
     

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