Phase Issues when Jumping UK Korg AC-30/6 (Top Boost and Normal)?

Discussion in 'Amps and Cabs' started by mewidmer, Oct 20, 2008.

  1. mewidmer

    mewidmer Member

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    say it ain't so.....

    so very interested in purchasing a VOX AC30TBX Reissue (Korg UK Versions) and one of the things that had me excited was ability to "jump channels"

    When I did some searching earlier several folks made the comment that the Korg UK model channels were out of phase. Does this create cancellation issues?

    Can anyone post with their own personal experience with the Korg UK's jumping the Normal/TB channels? Does it change using vibrato?

    I sadly have a non rationale attachment to the ac-30/6 and am economies away from an original model....

    thanks,
    Matt
     
  2. starfish

    starfish Member

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    IIRC this is true on the UK amps. I have two vintage AC-30's and the brilliant channel is out of phase with the normal and vibrato channels only if the brilliant channel is top boosted. This is because every triode stage inverts the phase. The top boost has an additional gain stage. That is the reason.

    You can use a direct box to flip phase, there are many options for this. Also, some boost pedals like the BJF Baby Pink will flip phase, likely due to an IC buffer.

    Good luck, it's an easy workaround and worth it if you love the amp.
     
  3. mewidmer

    mewidmer Member

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    Thanks for the input (sorry couldn't resist!):roll

    looked up the baby pink booster....so this pedal goes in between channels, you have at unity gain, flips the out of phase signal, voila in phase dual outs on your ac-30.....unfortunately seems like a expensive fix with the BJF pedals....they also mention though in the user guide that some stereo pedals also have this capability so another possible situation..

    very interesting.....

    I also found some interesting info over @ plexipalace....

    from a DC Jones...

    "It makes sense if you understand that the signals don't all come together at the same time. Signals that come in on opposite side of the phase inverter will be out of phase with each other. The vib-trem comes in on the opposite side from where the normal/brilliant channels come in, so they're "out of phase". What comes in on the normal/brilliant channel side is a composite signal of the two. They have been mixed before they reach the phase inverter. Any phase cancellation between exact frequencies has already taken place -- those signals are gone, having cancelled out each other. Keep in mind that that signal (especially amplified) ain't no simple thing -- it's loaded with harmonic overtones and the like and the majority of the signal, though out of phase with another will get through, because they're different signals. If the signals were exactly alike and 180 degrees out of phase, then they would cancel each other out, and hence no signal. Bottom line: normal and brilliant channel "do battle", frequencies are lost, most persevere, then the combined signal goes to one side of the phase inverter where the signal is split in the opposite manner of the vib-trem channel. Man, I hope this makes sense."

    net, it seems there are ways to make it work....can't wait till try
     
  4. mewidmer

    mewidmer Member

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    update on channel jumping......

    Was lucky enough to acquire a 64 AC30 bass that was modded to normal on the 'bay....

    Did my first channel jump earlier.....and the sound is simply amazing.....it seems like you get all of these harmonic's/undertones depending upon chord/voicing....on some there' this kinda lingering delay effect...others there's that slight beating as it sustains similar to when your tuning two strings.....

    for those who've not bothered to try....its def worth a shot....

    back to playing....:band
     
  5. michael.e

    michael.e Supporting Member

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    Just pick up a Radial ABY. Passive unit for $70 and well worth it. When you have effects in line on a Marshall or Tweed amp, the signal goes out of phase as well, I use mine all of the time and I am totally happy with the retention of tone.

    Well worth the money.
     

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