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One input jack for ab763 clone

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  • One input jack for ab763 clone

    What resistor would i use if i wanted to omit the second input jack on my ab763 clone? there is usually two 68k ohm resistors (grid stoppers). some builds i have seen online pictures used one input jack with two 68k ohm resistor. One 68K res would be ok? one input, 33k res? Thanks for the help

  • #2
    Originally posted by Dandrix View Post
    one input, 33k res?
    That's what I do, 33K. And I mount it on the grid tab of the preamp tube socket, not at the jack. Also, it's my practice to use carbon comp resistors for this function, though the debate rages on whether that matters or not. Also, you can opt for a smaller value "stopper" resistor, say 22K or 10K. Some say all the way down to 1K. Should you try to minimize the value of this stopper, there may come a point where you start to pick up radio transmissions or hear a scratchy noise as you turn the volume control in your guitar. If either/both happens, back up a step and opt for whatever value resistor doesn't open the door to problems. It is an area open to experiment.
    Last edited by Leo_Gnardo; 07-28-2020, 07:23 PM.
    Enjoy. Every. Sandwich.

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    • #3
      The hi gain input (No. 1) uses the two 68k resistors in parallel, resulting in a 34k grid stopper. Together with the input capacitance of the 12AX7 of around 150pF this constitutes a low pass filter with a corner frequency of around 30kHz. Using only one 68k grid stopper would lower the LP corner frequency to around 15kHz. Shouldn't make an audible difference.
      - Own Opinions Only -

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