What does a Phase Splitter do?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by bnwhtlw, Aug 18, 2005.


  1. bnwhtlw

    bnwhtlw Member

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    First, I want to apologize for my novice. I searched and read and looked around and tried to figure out what a phase splitter does, I just cant figure it out.

    I had a problem with the lead channell on my amp sounding too bassy...then I hit the boost and boom some treble. I replaced the 12ax7 (that I think is bad) with a 12at7 in the Phase Splitter socket and it sounded MUCH better. So does that make sense?

    I mean should that have solved the problem?

    btw Amp Gibson Supergoldtone GA30-RVH 2x 12ax7 for the gain channel

    I have the schematcis, but they look like gibberish to me.

    Thanx!
     
  2. Steve Dallas

    Steve Dallas Supporting Member

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    The phase inverter is unique in that it affects both channels in 2 channel amps.

    It has 2 basic functions, although your mileage may vary depending upon your amp's design.

    1. In a push-pull amplifier, half the signal needs to fed to each tube to be amplified by the output tubes and summed by the output transformer for transmission to the speaker. Since the power tubes work opposite each other in push-pull mode, the 2 signals being fed to the tubes need to be out of phase to keep the output constant (in simple terms). The phase inverter accomplishes this.

    2. Some amps mix signals from one or more channels into one side of the PI. Others send each channel into a different side of the PI. In this case, the 2 signals can be mixed to interesting effect. This also facilitates the ability to jump channels in some amps (assuming the 2 channels are out of phase with each other).


    HTH,
     
  3. VaughnC

    VaughnC Supporting Member

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    The output from an electric guitar is an AC (alternating current) signal which basically means that it consists of both positive & negative voltage excursions. When applied to an amplifier, the AC signal from the guitar passes through several preamplifier stages (usually 12AX7 tubes) and their purpose is to increase the amplitude of the guitars AC signal sufficiently to drive the final power amplifier stage, which subsequently drives the speakers.

    However, in order to increase the efficiency of the power amplifier stage, engineers came up with what's known as a push/pull amplifier circuit that we see in most (but not all) guitar amps. Put simply, in the classic push-pull circuit, one power tube amplifies only the positive voltage excursion of the already pre-amplified original AC signal from the guitar, while the other power tube only amplifies the negative voltage excursion. However, in order to drive the push/pull amplifier stage with the proper signal phases, the original pre-amplified AC guitar signal needs to be split into two phases with one signal being 180 degrees out of phase with the other....and this is the job of the phase splitter (also sometimes referred to as a phase inverter or PI) stage.

    The phase splitter stage sits between the last preamp and the power amplifier so it can affect the tone and gain structure of the entire amp. To some, a 12AX7 sounds better in the phase splitter stage while others feel that a 5751, 12AT7, or 12AU7, etc. sounds better....there's no right or wrong but what sounds best to you.
     
  4. bnwhtlw

    bnwhtlw Member

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    Ok maybe ears were decieveing me and the problem still kinda exists, though it is much better now. I think part of the problem is a bad batch of tubes. Already returned 2 AT's cuz they were crap. Damn EH tubes

    This makes more sense now, being that I have the ability to run CH1 and CH2 together at the same time. So, I assume this is where the splitter comes most into play. (?)
     
  5. VaughnC

    VaughnC Supporting Member

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    It doesn't matter how many channels an amp has, one or a million. In an amp with a push/pull output stage, all signals from the preamp(s) need to be split into two phases by the phase splitter in order to drive the power amplifier stage properly. Of course, there are variations on this theme with class A, AB, & B push/pull amplifier stages....but that's another discussion.
     
  6. bnwhtlw

    bnwhtlw Member

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    Ahhh, makes much more sense now.

    Thanx!
     

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