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Help with wiring EMG BTS preamp with passive pickups

Discussion in 'Pickups & Electronics [BG]' started by Matteo Marziali, Dec 17, 2015.

  1. ACTIVE-PASSIVE-EMG-BTS-WIRING_zpsdfec0t7s.jpg

    Hi there!

    I need some help with this wiring, I had to put and EMG BTS preamp with 2 passive Bartolini pickups, with active/passive switch and tone pot only in passive mode.

    Will 250 pots works for volume and tone?

    Where i put purple, orang and blue wires? (All the colors are random...)

    Will the battery still run in passive mode?

    Last edited: Dec 22, 2015
  2. 250 Ohms is not appropriate for any pot used in a bass. 250k Ohms, on the other hand, is what you want for the volume and tone pots.

    According to your diagram, the purple wire is the jack's ring terminal, which connects to the battery's negative terminal. The orange wire should connect to the output of the preamp. The blue wire should connect to the input of the preamp. However, you are wiring the active/passive switch incorrectly. That wiring keeps the tone control in the circuit, in active mode. To bypass the tone control in active mode, use this diagram:

    As long as you have a cable plugged in the jack, the preamp will always draw current from the battery. Active/passive switching simply bypasses the preamp from the signal path.
    Leo Smith likes this.
  3. JustForSport


    Nov 17, 2011
    You need a stereo jack to disconnect the battery from the preamp when you unplug.

    The other option is a full bypass, but that can get pretty complicated eliminating the POP! when switching the bypass on or off.

    Best to have a preamp bypass with a stereo plug to disconnect the power when unplugging.
  4. Thanks for the replay, but I still have some doubt…

    The jack in the diagram is an EMG stereo jack, the purple wire is the one of the two EMG outputs (see the pic in the right), the other output is the orange one; the wire from the battery’s negative to the jack’s ring is a black wire, that is also connected to the ground of the passive circuit (is this correct???)

    One of my doubt is: why there is 2 output form EMG preamp? Probably one of this wire will open battery’s circuit to avoid current drain, but how does it work? Which one is the “real” output??

    Yes Line6man, in my diagram (that I copy from Aguilar OBP-2) the tone pot is always engaged… but there is a wire that grounds the preamp input when in passive mode, why? It’s something concerned with current draining?

    I have a 3pdt on/on switch, can I use it to stop current draining, or will I got an horrible Pop?

    Thanks again!
  5. Grounding the battery's negative terminal is not correct at all! The battery's negative terminal needs to go to the ring terminal of the jack, otherwise you will be draining the battery all the time.

    There should only be one output from the preamp.

    The input of the preamp shunts to ground to help prevent popping noises when you use the active/passive switch. It has nothing to do with the preamp's current draw.

    Trying to switch the battery with a 3PDT switch is a bad idea, plain and simple. It will pop badly, and it won't be practical.
  6. Many thanks line6man!
    Now everythings is clear! I made a mistake coping the Aguilar wiring...

    Ok, so the battery's negative goes to the ring, the hot output go to the tip and the ground to the sleeve!

    Yes! The two wires indicate as output in EMG diagram are the hot output and the ground!....

    Since there is no ground for the preamp in your diagram , what happens if I use a 3pdt in this way? It's correct?

  7. It is not necessary to over complicate your wiring with a third pole. Two poles is sufficient to do the job, as shown in the diagram that I posted.
    Matteo Marziali likes this.
  8. JustForSport


    Nov 17, 2011
    In the first diagram, the battery negative goes to the sleeve terminal which does not complete the circuit thru the preamp until a plug is inserted, and the ring terminal allows the ground to be connected to the preamp negative (purple wire).
    Then, the circuit is back open when the plug is removed, as intended.
  9. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    hmm; the problem here is that's the "old" true bypass switching that leaves the preamp input open to cause noise and popping;

    in general you want the version that grounds the preamp input when bypassed, like this:
    (hey look, i wonder who made this diagram? :p)

    i don't see a way of patching in the passive tone here, so were it mine i'd go with the 3PDT switch, wire up two of the rows just like this, then use the third row to kick in the tone pot in passive mode.
  10. Thanks everybody!

    This should be the good one....
    Leo Smith likes this.
  11. hosebass

    hosebass Supporting Member

    May 8, 2010
    Los Angeles

    Did you ever build this circuit? Did it work?
  12. Yes. It works!
  13. Primary

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    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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