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Determining Amps Positive and Negative speaker output

Discussion in 'Amp Tech Center' started by drob, Dec 12, 2018.

  1. robrob

    robrob Poster Extraordinaire Ad Free Member

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    That's why I said, "no longer in phase."
     
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  2. Finck

    Finck Tele-Afflicted

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    Agree with Rob.
    Scientifically, a a very small time difference between two waves is sufficient to consider them "out of phase".
    Practically, when people refers to "out of phase" the meaning is "inverted by 180 degrees", what corresponds to speakers with reverse polarity.
    That's not necessarily a bad thing. It can even be useful, depending on situation.
    As example, in car audio, is very usual the usage of a subwoofer with reverse electrical polarity (therefore "out of phase" in respect to the other speakers), because, under certain circumstances, that avoids cancellation of some frequencies.

    Edit: now I see that I agree with Wally too...
     
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  3. Wally

    Wally Telefied Ad Free Member

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    Hence my statement that there are varying degrees of phase relationship. A partial phase relationship change is not the same as 180 degrees OOP, which really thins and weakens the resultant volume compared to in phase. Having the speakers wired OOP, these is a large phase cancellation effect....and after all that is where this thread has evolved from the Op’s Query on OT output wiring.

    The spinning dancer in the middle of the floor may be hooked on phase shifts, correct??
     
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  4. W.L.Weller

    W.L.Weller Tele-Holic

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    The manufacturer calls this a "phase computer," play through this to the phases of the moon!
     
  5. Andy B

    Andy B Friend of Leo's Silver Supporter

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    Traditionally Green = +, Black = -.
     
  6. Lynxtrap

    Lynxtrap Tele-Holic

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    No I'm not serious, I should have added a ;)
    Like I said in the previous post, this concept is proposed and discussed now and then in forums etc.
    Personally I don't have an opinion about it, but yes, it seems a bit ridiculous.
     
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  7. Lynxtrap

    Lynxtrap Tele-Holic

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    I'm not sure if it's allowed to link to other forums. I guess the moderators can remove it if it's not.
    This is a link to a thread where the "single speaker out of phase with the guitar"-issue was debated extensively.
    Reading it now, I can see that I do seem to have opinions about it :)
     
  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Out of phase with the guitar? That's funny.
     
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  9. Bill Moore

    Bill Moore Tele-Afflicted

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    Seems phase with the guitar would be determined by which channel one was using on a standard AB763 circuit.
     
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  10. Wally

    Wally Telefied Ad Free Member

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    Plug into the Normal channel. The instrument’s output will be amplified through two preamp gain stages. Plug into the vibrato channel and the signal will be amplified through three preamp gain stages. The only time that phase steps into the equation is if one combines those two channels at equal channel strength.....then, there will be phase cancellation.

    If one has a pickup in a guitar with a switch to flip the wirning(phase) of that pickup’s output....not the relationship of the coils of a humbucker to each other but the ‘beginning and end’ of the coil circuit.... then one could hear whatever difference in the guitar’s “Phase” one might hear through either of those channels alone. I venture a guess that not one in twenty would get such a choice correct in a blind test.....maybe none in twenty.
     
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  11. Lynxtrap

    Lynxtrap Tele-Holic

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    Man, couldn't help but get into this again when reading through that whole thread.

    In case you don't want to read it all, Mr Martin Manning summed up the whole thing neatly as follows:

    Okay, to sum up we have three possible interactions that might be affected by the electrical phase of the speaker connection, and there is anecdotal evidence that there can be an audible effect from reversing the speaker phase.

    One of these interactions is the acoustic feedback to the guitar, which in turn results in electrical feedback to the amplifier. This is full of other variables that will change the phase of the sound waves reaching the guitar, including the highly variable position of the guitarist relative to the amp. I am inclined to believe that speaker phase is less important here.

    A second is the mechanical feedback from the speaker to vacuum tubes and other non-ridgid components in the amplifier, resulting in electrical feedback. This is much more controlled, and very much so in the case of a combo amp configuration. IMO, it is not unreasonable to think that the speaker phase will affect this process and that the result would be audible.

    The third is the direction (+ or -) of the initial pressure pulse in the sound wave produced by the speaker as determined by the initial direction of the guitar string movement upon release. Whether a human can detect this is questionable, but I could imagine a blind test where pairs of single pulses are sent to the amplifier and a listener is asked to identify any difference between the first and the second, each of these being of a random polarity.

    Another thought: If the initial pulse direction is important, and the feedback from the speaker to the chassis is as well (meaning that for each of these one speaker phase relationship sounds better than the other), then it's possible that the "better" speaker phase for one could be the less desireable one for the other. The best combination might then require selecting the phase of the pickup signal and the speaker, or alternatively that some amp topologies (number of inverting stages) might be better in this regard than others for a given guitar.
     
  12. SSL9000J

    SSL9000J Tele-Meister

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    And this is how simple things become complicated. But seriously folks, I can't help but wonder if a single speaker's "+ / -" makes a difference with regards to the winding of the voice coil. IE, is there a "top / bottom" or "inside / outside" of the speaker coil and, if so, which way should it "face" the secondary coil of the output transformer? I'm thinking along the lines of the old "outside foil of non-polarized capacitors should be closest to ground" philisophy. At least in theory.

    Of course, this may just be another proverbial can of worms.
     
  13. Bill Moore

    Bill Moore Tele-Afflicted

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    Wally, if the signal between the two channels is out of phase with each other, wouldn't the guitar signal be out of phase with the speaker, depending on the selection?
     
  14. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Yep, the more you analyze this subject the less sense the theory makes.
     
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  15. joe_cpwe

    joe_cpwe Tele-Afflicted

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    I've been to gigs where band members were out of phase with eachother. Bigger problem IMO
     
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