Adding Active/passive switch and Passive tone control

Discussion in 'Pickups & Electronics [BG]' started by SubNoizeRat3691, Mar 2, 2014.


  1. SubNoizeRat3691

    SubNoizeRat3691 Supporting Member

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    Hello all, I am not great with electronics/wiring, so my first question is.. Is this even possible??? :help::help::help:

    I would like to add an Active/Passive switch to my Fender Precision Bass Special (Vol, Blend, Bass/Treble stack, Mid Control Layout) and along with a switch for the preamp/battery, I'd like to add a passive tone control.

    Second question is, where could I find a wiring diagram for such a layout??

    It seems like I would have to swap out the Mid control for a Mid/Tone stack, to add the extra control.

    I really like the tone of this bass, but I would also like a passive type tone in the same package.

    Thanks for any advice you can give me!!
    Nick
     
  2. line6man

    line6man

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    I would assume you want the tone control to only be in the circuit for passive mode?

    That's done like this:
    [​IMG]

    Why do you want a power switch? That's generally not a good idea.
     
  3. JDLowEnd

    JDLowEnd

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    I would search for the diagram of a reggie Hamilton bass and try that, see if it's what you need!
     
  4. SubNoizeRat3691

    SubNoizeRat3691 Supporting Member

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    I was not sure if I should switch the battery or not. Would the passive mode still work without a battery in the diagram above??

    Is it possible to put the Tone control in a concentric stack with the Mid control???
     
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  6. SubNoizeRat3691

    SubNoizeRat3691 Supporting Member

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    Is that a DPDT switch??? I really don't know much about electronics lol
     
  7. line6man

    line6man

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    Passive mode means that the preamp is bypassed from the circuit. Whether or not the preamp receives power is irrelevant, if it is not in the signal path.

    It would probably be difficult to find a concentric pot for passive tone/mid level. The passive tone should be a 250k or 500k audio taper, while the mid level control should be a 25k, 50k or 100k linear taper pot with a center detent. Concentric pots usually have two of pots the same value and taper.

    Yes, the switch is DPDT On/On.
     
  8. SubNoizeRat3691

    SubNoizeRat3691 Supporting Member

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    Could I stack the Volume and tone? would those pots line up value wise???
     
  9. line6man

    line6man

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    Yes. Assuming you like audio taper volume pots.
     
  10. SubNoizeRat3691

    SubNoizeRat3691 Supporting Member

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    what is the difference between Audio taper and Linear taper??? I use my volume knob for most of my volume control live, never dimed, mostly somewhere in the middle.
     
  11. wmheilma

    wmheilma

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    I recently added a pull passive option to an older bass. There was no place to put the passive tone pot, but out sounds fantastic without it. One thing I learned the hard way is that you'll need to as a couple of resisters to keep it from going "pop" when you engage the preamp with your amp cranked up. I used a 500K pull pot.
     
  12. line6man

    line6man

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    [​IMG]
     
  13. SubNoizeRat3691

    SubNoizeRat3691 Supporting Member

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  14. khutch

    khutch Praise Harp Supporting Member

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    The volume control on that bass is part of the preamp so it is difficult to access it in passive mode. Plus, as line6man suggested, it is a 25k pot, not what you want in passive mode. Someone mentioned the Reggie Hamilton bass and it has the same preamp with an active/passive switch. In that bass the volume control is a dual pot with one section a 25k, the other 250k. This place claims to sell these pots so you should be able to get one there if they really stock them (I've never done business with them so I don't know). In theory you could replace the volume pot on your preamp with this one to get a passive volume pot. There are two issues with that. One is that the pot body as well as the pot leads are soldered directly to the preamp board which makes it a bit trickier to do the swap. The other is that the preamp mounts directly to the pot and while the routing on the Reggie Hamilton bass is deep enough to allow room below the control plate and pickguard for a dual section pot plus the preamp board the route in your bass may not be deep enough since it was designed with the single section pot in mind. I'd check that out before buying the Reggie pot.

    Assuming that works you still need to find a mid/passive tone pot and the mid pot needs to be 100k while the passive tone pot wants to be 250k or higher. Perhaps the mid/tone pot in the latest American Deluxe Jazz basses would be what you need but I don't know where you could find one. I don't see a diagram for the latest models on the Fender site so I don't know what the Fender part number is or what the values are either. An option that should work is this "Danelectro pot". The 100k section is what you need for the mid control and the 1Meg section would work for the tone control. They don't mention if it is detented so I assume not and I don't know if a full size pot fits in that location, I believe the original is a mini.

    I have a Reggie Hamilton bass which already has the proper volume control of course. But I am thinking of modifying the passive mode so that it only runs the P pickup and then using half the blend control in passive mode as a tone control. To do that would require a 4PDT active/passive switch. My goal is to get a passive P bass configuration that would satisfy even the passive P bass purists but it also acts as a passive limp home mode in case of a battery failure. If you wire the A/P switch as line6man suggests, which is the same as shown on the Reggie Hamilton wiring diagram, the bass will play in passive mode without a battery.
     
  15. RobbieK

    RobbieK

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    Yeah, doing all this in two pickguard holes might be a bit difficult or expensive.

    You could check out the warwick site for an MEC specialty pot that has a push pull switch on a stack. I would think they'd have either a 250kA stack (vol/passive tone) or a 50KB stack (to add the switch to your current active treb/bass arrangment). But this would be pretty expensive.

    You could drill a little hole and have a toggle switch for the active/passive, then something like this as your vol/passive tone.

    You could also route a section out and have an extra control closer to the pickup for your vol/active-passive push-pull to free up a hole for your passive tone pot.

    As khutch as said though, the existing (25K) vol is not only soldered to the circuit board, but not suitable for passive use, so you may have to add a jumper or cut a track or something to hard wire the preamp without the vol pot, depending on how the circuit is layed out. (Plus, desoldering a pot from a circuit board is tricky if you are new to soldering.) Then use a 250K on the input of the preamp. There's a good chance this will change the tone of the active sound slightly though. You'll also have to heatshrink or mount the circuit in some other way.

    If you really must have both a 25k vol after the active pre and a 250K vol in passive mode, it is do-able with the right pot, but you'll probably need more than the 2poles that are on offer with a typical push-pull pot's switch, especially if you want true bypass. Plus you can't have a stacked vol and passive tone, as your vol would be a dual gang (25k/250k) pot in its own right.

    In summary; It is certainly all do-able, and actually a pretty common way to wire a bass, but you'll have to decide a) if you want to drill and/or route your bass, and b) if you need your active sound to be exactly like it is now
     
  16. khutch

    khutch Praise Harp Supporting Member

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    The OP's bass has four holes for controls already, it is the active P-Bass with the J bridge pickup too. Even four holes makes it difficult however. Another option is to consider carefully how important the blend control is. If you really never use it to finesse the blend between the two pickups you could replace it with an ON-ON-ON toggle switch to select one pickup, the other, or both which is how a whole lot of us actually use our basses. The blend pot in these basses is wired in ahead of the preamp so it is easily removed without distrubing the preamp operation. So you could remove it, replace its function with a toggle switch and then put a stacked pot in that place to provide the passive mode tone and volume controls. There are many ways to do this job but each requires a compromise you have to be comfortable with. Unless you can find that American Deluxe mid/tone pot somewhere....
     
  17. RobbieK

    RobbieK

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    Oops. Apologies. I thought it was a regular P.

    But that's great news! All you need is one of these. Replace your mid control with this guy and use its switch as an active-passive.

    And one of these. This will be your volume and passive tone.

    As I mentioned, running the vol before the pre will roll just a tiny amount of treble off in active mode, plus you'll have to re-wire the output of the pre to ignore the existing volume arrangment, but these are simple things for a decent tech...
     

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