could someone please double check my wiring diagram?

Discussion in 'Pickups & Electronics [BG]' started by pricey, Apr 11, 2014.

  1. pricey


    Jun 6, 2008
    Hi, I'm planning on adding an extra pickup to my 2002 Aria bass. Below is a quick before/after photoshop mockup of my plan.


    The bass uses an ME3 active pre-amp. The suggested wiring diagram for this system is shown here:


    However, in my Aria, they have chosen to wire it like this, with a DPDT for switching the active electronics on/off and another DPDT for tapping the north coil of the single pickup. (only one side of each of these is used however).


    My plan is to add an extra humbucker, and have 4 switches. I'm going to retain the active/passive switch, but also add 3 ON/ON/ON DPDT switches. One will toggle the pickups 'Les Paul' style, and the other 2 will allow me to switch each pickup between SERIES/PARALEL/NORTH TAP.

    Here is my planned wiring diagram, I was just hoping that somebody could have a quick scan of it and make sure I haven't made any silly mistakes as my knowledge of this kind of thing is pretty limited and it'd help me with any future projects too :)


    The wiring scheme for each pickup is this:

    North Start: orange
    North Finish: green
    South Start: black
    South Finish: white

    North Start: black
    North Finish: red
    South Start: white
    South Finish: green

    Thanks for taking a look :)
  2. Your active/passive switching and volume pot placement are incorrect. The volume pot needs to go before switching, because you need the signal impedance to be the same for both active and passive modes. The active/passive switching should be done like this:

    Three way pickup selection is typically not done in that fashion, because it requires the use of DPDT Center-On switches, rather than more common SP3T switches ("DPDT On/On/On").
    If you want to use a standard SP3T switch, do it like the mini toggle shown here:

    Minor technical point; you are confusing coil splits with coil taps. The wiring shown is for coil splitting, not tapping.
  3. pricey


    Jun 6, 2008
    Ahhhh okay, that makes sense with regards to pickup switching, the switches I've ordered are of the SP3T type so I'll change the diagram to reflect that.

    That is interesting regarding the active/passive switching, as it suggests that the way the bass is wired from the factory is not optimal. When I switch it from active to passive at the moment, I do notice a big volume drop and the output sounds quite weedy, even though the active controls were set to the middle position before switching, which would suggest the outputs should be similar. Is this perhaps because of the impedance mismatch?

    I'll change the wiring diagram now to reflect your suggestions.

    Thank you very much! :)
  4. The problem with wiring an active/passive switch like that is the fact that the preamp's input remains connected to the signal in passive mode. This causes a decrease in input impedance on the pickups, because the preamp's input impedance is parallel to the input impedance of whatever the bass is plugged into. If both impedances are 1M Ohms, for example, the total impedance will be reduced to 500k Ohms.

    A drop in input impedance may explain the volume issue, though it usually leads to a loss of high frequencies, rather than overall volume. The volume issue is more likely to have been caused by the volume pot, if it is a 25k or 50k pot. Since the output impedance of a preamp is almost always lower than that of passive pickups, volume pots are usually placed before active/passive switches, so that the signal impedance through the volume pot does not change as the preamp is removed from the circuit. If a volume pot is placed after active/passive switching, then you get one of two issues, depending on the pot value chosen. If a low value pot is chosen (25k, or 50k), it will work fine for active mode, but it will load down the signal in passive mode, causing a noticeable loss of output. If a higher value pot is chosen (250k or 500k), it will work fine for passive mode, but in active mode, it will behave more like an on/off switch than a volume control, because of the relatively large resistance, compared to the signal impedance.

    The proper way to do active/passive switching is to do "true bypass" switching, to fully remove a preamp from the signal path in passive mode. This is similar to what is done on stompboxes, but in the diagram I posted above, the switch is also configured to shunt the preamp input to ground in passive mode, in order to reduce switching noise.
  5. pricey


    Jun 6, 2008
    Thanks for that detailed explanation, it makes a lot more sense to me now.

    I will wire it the way you suggested initially and see how I get on :)