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Here we go, more PJ help needed for a n00b

Discussion in 'Pickups & Electronics [BG]' started by PipeRain, Jan 26, 2013.

  1. PipeRain

    PipeRain Operator Of Pointy Basses Supporting Member

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    [tl/dr] Why do my PJ equipped passive and passive pup/active pre basses have weird volume blending issues?

    First off, let me start by saying that I am a n00b retread. I played 20+ years ago, but mostly just cared about being as stupid loud and sounding as "Metal"* as possible. Now, all these years on, I am picking up the bass again. I still love my metal and thrash, but am looking to expand my tonal palette a bit, specifically to play at church.

    I have an old bass that I had a set of Seymour Duncan "Active EQ's" installed in. It has a volume/volume/tone with a pickup selector switch. Yeah, I know, different but it is what it is and I have gotten used to and like the setup. The tone is pretty bright and certainly does not lack for punch, however it is definitely a "Modern" sound. I fell into a couple of other basses in the last week, an Ibanez GSR200 and a Squier P-Bass Special. These two are in the running for a "Church bass" as well as giving me the option of being more sonically rounded. Now I am up to three PJ basses.

    The SD equipped old-timer is pretty well balanced across the pickups for volume. I can switch back and forth between pickups or play both and the volume is consistent. However, with the other two basses this does not hold true. The Squier is passive stock pickups and the Ibby is stock pups with their "Phat bass" preamp. If I run both pups wide open on these two then roll one of the pickups off slightly, say 10-15 percent, the overall volume seems to go up pretty noticeably. Continuing to roll the volume off then seems to have a more expected result. Somehow, this just doesn't seem right and I am at a loss to explain why this is.

    I think I have seen this anomaly referenced here in passing on TB, but for the life of me I can't find any of those references now that I need it. As near as I can tell it's down to one of these things:
    1. This is just the way PJ setups work and I have to deal with it.
    2. This is a function of passive, but not truly active, pickups.
    3. This is a function of controlling the blend via independent volume knobs, but throwing a switch in the mix fixes it.
    4. It is not, in fact, a volume issue but rather a frequency issue; attenuating the volume of one of the pickups enhances or cuts frequencies that cause this "Effect".
    5. I'm clearly just insane, pay no attention, move along and don't poke the badger.

    I should note that the effect is more pronounced when rolling back the J pup as opposed to the P, which gives rise to theory number 4.

    Thank you in advance for any wisdom you can provide.

    *How exactly does one sound "Metal"? Does that mean sounding like a sheet of 1/4" steel being pounded with an aluminum bat?
  2. line6man

    line6man

    Joined:
    Jun 20, 2008
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    This is an insertion loss issue inherent to the VVT setup. When both volumes are up, output impedance drops as the impedance of each pickup loads against the other. By rolling a volume pot down a bit, you introduce a series resistance between one pickup and the output, but this also has the effect of increasing the output impedance of that pickup. With the increased output impedance of one pickup, there is less loading on the other pickup.

    It is common for the effect to be most prominent when rolling down the J pickup in a PJ setup with a single coil J, because the J pickup naturally has a lower output impedance than the P, so its load is relatively direct. However, the output impedance of two active pickups from the same manufacturer should not significantly different. I would think that both pickups would have the same opamp or discrete transistors, configured for a similar output impedance.
  3. PipeRain

    PipeRain Operator Of Pointy Basses Supporting Member

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    Thank you line6man.

    Bearing in mind what you are saying, can this be alleviated by going to a single volume, or switching the J pup in either bass to a humbucker? I have an SD classic stack J pup I could toss in one....

    [ETA] If I went to a single volume control, I would solve the volume balance issue, but would still see an overall output drop, correct?

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