Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

Bypassing Preamp

Discussion in 'Pickups & Electronics [BG]' started by BlacksHole, Jun 17, 2003.


  1. BlacksHole

    BlacksHole

    Mar 22, 2000
    Rockville, MD
    I mistakenly posted this in the basses forum, so now that I've realized my error, I'm trying it here. Thanks for any info:

    Rewiring pickups questions
    I have a Bass Collection fretted 5 string that gets too much hum and buzz, particularly if I turn up the treble as one would expect. This bass is active and I believe that it is an active preamp with regular p.u.s - is there a way I can tell easily (I bought it used)?

    What I was thinking of trying is to take the 2 p.u.s (P & J) and wire them directly to an input jack. This should give me no volume, tone or blend control - would I be correct in assuming that the blend would be approximately 50% give or take a few percentage points based on the output of each p.u.?

    Would I basically have the bass and treble on full without the tone cotrol pots bypassed?

    Using such a setup, I should get a lot less hum and buzz, shouldn't I?

    Also, I would presume that the output would be considerably lower since the preamp would be disengaged - correct?

    To do this I was thinking about adding a switch that would enable me to either go straight to the p.u.s or to use the preamp and my guess is that even with the switch and the preamp there, that I'd get virtually no hum or buzz when I'm in straight wire mode - or would there presence and connection by the switch still bring in the buzz?
     
  2. BlacksHole

    BlacksHole

    Mar 22, 2000
    Rockville, MD
    I guess my ?s were either too basic or too convoluted in phrasing. Phooey.
     
  3. i wired my pickups straight to the jack. it didn't really reduce the hum that much. you might want to try some extra shielding, maybe?
    i dunno much about this stuff, or anything.
     
  4. BlacksHole

    BlacksHole

    Mar 22, 2000
    Rockville, MD
    Thanks for the reply. I really expected it to be the preamp that caused all the noise. With it just straight wired, there doesn't seem to be much left to shield. Obviously, I don't know much about this either.
     
  5. doing this will tell you if its the pickups which are causing the hum...do them one at a time..
    you can wire them via a vol pot to give some control if necessary.
    are they single coils
    :)
     
  6. FBB Custom

    FBB Custom TalkBass Pro Commercial User

    Jan 26, 2002
    Maryland
    Owner: FBB Bass Works
    Here are a few comments:

    Preamps are generally well shielded.

    Boosting the treble (turning up the treble with an active preamp) boosts the frequencies where the noise/hum probably sits (so it gets louder).

    Bypassing the preamp will give you flat (no boost no cut) EQ and a high impedance signal. High impedance signals can actually pick up noise if you use long cords.

    The noise is probably coming from the pickups.
     
  7. BlacksHole

    BlacksHole

    Mar 22, 2000
    Rockville, MD
    Rats - if the noise is from the p.u.s themselves then it's more expensive to fix, i.e., I'd have to get new p.us rather than just reroute wires. It's a nice bass, but not a great bass and I have others, so I don't know how much I'm willing to put into it to get it to work better. Perhaps after a bypass experiment (if I don't totally mess everything up), I'll take it to someone who actually knows about these things and get they're advice/help rather than continue experimenting. Hopefully, I can find someone local who is good at this stuff.