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Can an amp flip the phase?

Discussion in 'Amp Central Station' started by xjazzy, Jan 27, 2018.

  1. xjazzy

    xjazzy Friend of Leo's

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    I have three amps: two combos and a head+cab.
    I usually use two amps at the same time and I had to make sure all the speakers are in phase so I had to switch the wires on the speaker in one of the amps and they're working fine. Even when I'm running the three at the same time they're all in phase with each other.
    Yesterday I had to run the head through one of the combo's speaker and I noticed that, when paired with the other combo, they're out of phase!
    When I'm running both combos together they're in phase but, the head seems like it's flipping the phase!
    Is that possible?
     
  2. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    More than possible.
    Consider this.
    Signal comes in and goes through a pair of triodes before hitting a single output valve. The first triode, output comes from the plates. Phase maintained.
    The second triode pair, the first triode is used as a cathode follower. Phase inverted. Hits the second triode and the signal is pulled from the plate. An inverted signal compared to the first triode pair gets presented to the power valve.
    Have a looksy at the schematic for your amp. Equal numbers of cathode followers = phase maintenance. Odd number = phase inversion relative to the original signal. And that's before you look at the output stage :)
     
  3. xjazzy

    xjazzy Friend of Leo's

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    Thanks. It makes sense.
    Since they're all in phase with their own speakers, I thought they would keep it when I mix different amps with different speakers.
     
  4. Finck

    Finck Tele-Afflicted

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    Let's say you want to connect and play a certain signal source (a guitar, an ipod, whatever) to 2 different amps at same time. If you put their cabs side by side and one of the amps is inverting the signal phase (as result of what have been explained by Vintage SG), you can experiment a loss of sound pressure, since when the speaker(s) of one cab moves forward, the speaker(s) of the other cab moves backward, causing some cancellations.
    In that case, you can invert the connection polarity of one of the cabs to its amp (no matter what).
    So, even with the amps working out of phase, the speakers will move with synchronicity, which will solve that issue.
     
  5. kennl

    kennl Tele-Afflicted

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    Construct a speaker cable with the + and - connections reversed on one end.
    I would use unique plugs or a different jacket color to differentiate that one from my other speaker cables.
     
  6. Teleterr

    Teleterr Friend of Leo's

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    ?
    Screenshot_2018-01-27-09-44-16.png
     
  7. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    !
    I may have it butt-about-face about which output flips and which maintains phase ( embarrassed )
     
  8. Teleterr

    Teleterr Friend of Leo's

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    It depends on the circuit, alot of times I ve followed the excellent amp threads here where a driver might be not obviously using the Cathode as an input, but is and doesn t invert, even tho at first glace one might not think so. So I thought maybe thats what you were referencing. I m always messing my posts up, so don t be to hard on yourself.Sometimes brains just turn upside down.
     
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