79 Traynor and Icepickin' - Baxandall Tonestack?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Biller, May 22, 2011.

  1. Biller

    Biller Member

    May 22, 2011
    Washington, DC
    I got a '79 YBA-1 that I brought back to life and it's still spiky in tone. Any notion if the baxandall-type tone stack or the stock cap values compromise the gearing for a guitar tone? I gotta dime the bass, 2 o'clock the mid, and then no more than noon the high and presence- but even there, still kinda icepicky.

    There's also a 6800p cap between the stack and the PI whose mission I just don't understand.

    I've done a couple mods based on the kilback.net/traynortweaks2.htm doc and she's a beautiful working beast, but the fangs are still a little too sharp; want a little more sing, little more sizzle and silk...

    I tossed a clip of the stack's schematic in for good measure. Any thoughts would be greatly appreciated.

    Much thanks-



  2. TweeDLX

    TweeDLX Member

    Mar 24, 2008
    Port Angeles, Washington
    Your picture didn't work. seeing a schematic of what you actually have in there would help. Turn the Presence knob down. That's not a Baxandall tone stack. They don't have a mid control, do they? The .0068 is probably the coupling cap to the PI. If there are two caps in a row (in series), try removing it. If not, change it to a higher value like .01 (schematic shows .02). Fender uses .001 in a lot of their stuff.
  3. teemuk

    teemuk Member

    Apr 21, 2009
    The presence and midrange controls look like "twin-T notch filters", first one being of active type. They are not baxandall controls (which BTW can indeed come in versions with one or more controllable bands in addition to treble and bass bands).

    I'm not entirely sure but I think the "presence" might actually lend itself to both boosting and cutting. The midrange control looks to be cut-only.

    The bass-treble stack is a variation of the generic version of the classic guitar amp tonestack, mid control is just replaced with a fixed resistor value.

    They likely designed it this way to minimize interaction you would get from a generic tonestack that incorporates a midrange control.

    None of this stuff "compromises tone", basically it just changes it at best. Adjust the knobs - if you have to, eyes closed - and when it sounds fine you have your settings.

    6800pf cap is for coupling because the grid of the PI has DC voltage potential.
  4. Tone_Terrific

    Tone_Terrific Supporting Member

    Dec 26, 2004
    A stock Bassmaster sounds fine.
    But, jumper the channels together and adjust ch levels for tonal balance.
  5. parkhead

    parkhead Member

    Jul 29, 2009
    change c6 to 250pf
    change c7 to .02


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