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Thread: Phasing issues in preamps?

  1. #1
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    Phasing issues in preamps?

    I keep running into little references here and there about out-of-phase issues in preamps, or maybe it's just amps in general. Don't know. I can't seem to find out anything about the subject though.

    I'm building a preamp - sort of my own (by necessity) adaptation of a dumble preamp. It'll have two tubes: Three stages at any given time - two stages in parallel that will never be on at the same time, and two more in series. There'll be a TMB tone stack after the last stage, leaving from plate (not the cathode). I don't know how much of the above matter, if any, but there it is anyway.

    Can somebody give me a quick lesson on phasing, or point me to a link? Will I have any problems with phasing?

    I've built a single-tube version of this already, and experiments with adding another tube stage from my Kalamazoo Model One give me what I want with no problems. I want to be sure though before I do any more soldering.

    Thanks, guys.

  2. #2
    Senior Member hasserl's Avatar
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    May 2006
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    Phasing is only a problem or concern when you have 2 circuits running in parallel at the same time. If the 2 circuits have opposing phase, then there can be cancellation of frequencies when they combine. Since your 2 parallel circuits will never be operating simultaneously this shouldn't be a problem for you.

    But then there is the issue of absolute phase of an amp (i.e. a positive input signal from the guitar results in a positive output signal at the speaker), but that can really get complicated and is probably not worth worrying about IMO.

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