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LOUD pop when engaging or disengaging preamp? (ACG)

Discussion in 'Pickups & Electronics [BG]' started by Rusty the Scoob, Jan 14, 2014.

  1. Rusty the Scoob

    Rusty the Scoob

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    I wired up an EMG P/J with an ACG, but with a bypass switch so I could also get those pure P tones as well. I used an EMG blend pot and the single-pickup configuration for the ACG, it's strictly doing the filtering function, the volume, blend and tone are all EMG pots with the ACG inserted between the master volume and output jack.

    My bypass switch is wired thanks to some help from Line6man who provided the following diagram (he drew it on a push/pull pot but I used a DPST mini-toggle switch instead), which works well but has a very loud POP when I flip the switch in either direction.

    [​IMG]

    I've seen various suggestions to add a resistor and/or capacitor between some of the lugs or between some of the lugs and ground, but I'm not sure what to try first or what danger there is of causing problems.
  2. coughiefiend

    coughiefiend

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    K... I'm curious about this too.
  3. Rusty the Scoob

    Rusty the Scoob

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    Here is a more complete diagram of how it's wired. I used an EMG circuit and inserted the ACG between the volume pot and output jack.

    [​IMG]
  4. Skelf

    Skelf Gold Supporting Member

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    Disclosures:
    Builder AC Guitars.
    I spoke to John East about this and he suggests the following.
    The volume control keeps the output cap at ground potential, without it, the cap –ve will float and cause a big thump when switched.

    It needs a 10K ‘bleed’ resistor between the output hot and ground, one thing will be cured.


    The pre-amp was not design to be used without the supplied volume control.
  5. Rusty the Scoob

    Rusty the Scoob

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    Thank you!!! I never thought of asking John since I wasn't thinking of it as an ACG problem at all, just a preamp switching problem. I'm a big fan, this is my 4th East-equipped bass and the first time I went outside the normal installation.

    I only sort-of understand this:

    So there's a cap at the output that charges up and then discharges when I flip the switch? And it bleeds off via the volume pot?

    But this is pretty straightforward, I'll try it tonight.

    This probably explains another symptom I didn't add because I thought it was either my imagination or a red herring: My pedal tuner, a nice Sonic Research Turbo Tuner ST-200 has a mute function. With my other basses (even my other bass with the ACG installed normally) or this bass with the ACG bypassed it's perfectly silent, but with the ACG engaged there's that same big Pop when I mute the signal.
  6. John East

    John East

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    Owner of E-Pro & East UK
    Just to say, the resistor would fix the issue highlighted ref output cap of the preamp.

    But the switch may still cause a noise for other reasons. Let us know how you get on.

    With this full bypass switch circuit, one of the issues is that the input to the preamp is either fed by the pickups/vol-controls etc or grounded, but whilst at mid switch point, when the switch wipers are not connected to anything, the input is effectively floating in 'mid air'. This itself can give rise to a click as well.
  7. Rusty the Scoob

    Rusty the Scoob

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    Skelf and especially, John, you guys are The Man! Pop is totally gone, I just bought a 5-pack of 10k Ohm resistors at Radio Shack, inserted the closest one to 10k (they ranged from 9.4k to 9.9k on my budget multimeter) into the correct screw-in terminals and the pop is totally gone. Maybe a tiny click as you said but nothing that'll blow speakers, it's hardly even noticeable. Also the mute on my pedal tuner is now silent in all modes.

    Thanks for the awesome service, I counted wrong before, this is my 5th East-equipped bass and won't be the last! (2 ACG, a BTB-01, a P-Retro, and an MM-Retro) I have my eye on #6 as we speak, another P that I think will soon get a similar but different setup than the one in this thread.
  8. John East

    John East

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    Owner of E-Pro & East UK
    Very good, a result!

    Glad we were able to help from some distance.

    The exact resistor value is not crucial, as it's only job is to keep the output end of the capacitor, at ground/0V potential, whilst not being any load for the audio signal. The reason you get a pop or thump is that there's some sort of difference in voltage or signal between the two sources.

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