MIM Jazz bass modded with a switch..what is it?

Discussion in 'Pickups & Electronics [BG]' started by lupien, Aug 4, 2009.


  1. lupien

    lupien

    Aug 17, 2008
    Ottawa, Canada
    Hi,

    I just got this Jazz bass not to long ago (see pic below). The previous owner swapped the pickups for US Jazz HM pickups and also added this switch in it. Now I have no clue what the switch is. All I know is that it only affects the bridge pickup. When the switch is on I get much more tone from the pickup and then off seems to cut back the tone.... Pretty weird actually.

    I thought maybe it was a S/P switch but I figured that should also affect the neck pickup.

    So maybe someone here can help me out. Here are some pics of the wiring.

    Neck pickup: All 3 wires go to the neck Volume pot.
    Bridge pickup: Red and White wires go in the Switch. The "bare" wire which I assume is the ground goes in the Tone pot.
    Switch: 1 black wire goes from the switch to the bridge Volume Pot. Soldered together with the other wires right on top
    1 brown wire goes to the bridge volume pot on one of those pins that stick out of the pot.

    A black wire connects all 3 pots soldered right on top of the pots.
    A white wire connects all 3 pots but this one is soldered on the little pins that come out of the pots.

    Thanks

    96MIMJazz002.gif
    96MIMJazz009.gif
    96MIMJazz010.gif
    96MIMJazz011.gif
     
  2. Best guess is that it's a series/parallel switch. I did the same mod to my jazz bass, sounds great.

    When you flip the switch, does it get a little louder, slightly bassier, and only the first volume control works? That's a series/parallel switch.
     
  3. lupien

    lupien

    Aug 17, 2008
    Ottawa, Canada
    Actually both volume still work. When I flip the switch it doesn get louder but only the bridge pickup. if the bridge volume is off and only the neck pickup is on nothing happens..
     
  4. Beej

    Beej

    Feb 10, 2007
    Vancouver Island
    Judging by the photo of the wiring of the switch itself, I'd say its a phase switch. I installed one on my own jazz ages ago and found I almost never used it.

    Try this to confirm:
    Plug in, turn up the treble all the way, palm mute all of the strings and then strum across all of the strings with a pick or your fingernail. Hit the switch and do it again, if its a phase switch, you should hear a faint phase effect, and that will be the main difference between the two settings...
     
  5. kingquasar

    kingquasar

    Jul 29, 2009
    Beat me to it. An easier way to test is to turn the neck pickup volume all the way down so you can only hear the bridge pickup. Flipping the switch then should yeild no audible difference - i.e. the switch only affects the pickups in RELATION to each other.

    -kQ
     
  6. lupien

    lupien

    Aug 17, 2008
    Ottawa, Canada
    Thanks for the info. So I tried what you mentioned but I can't here the phase you are talking about... Maybe i`m not understanding what you mean but all I can hear thats different from the switch on or off is the tone seems more "full" on the bridge pickup only when its on.

    When you say phase switch are you talking about a phase reversal switch?

    I also tried this and with only the bridge pickup on I do here a difference when I flip the switch..


    I tried reading whats on the switch but couldn't read it until I took a macro photo of it. It says C&K 7201 on the switch... Not sure if that rings a bell for any one. I did some research on the switch and it seems to only be a standard toggle switch..?? But looking at online pics I see the switch does not have the little wires going from poll to poll on the switch like mine has.. See pics below for closeups (Clear plastic on over the wires).

    Thanks

    96mim003.gif
    96mim006.gif

    So if the wires criss cross on the switch like that is it reversing the signal of the pickup?
     
  7. kingquasar

    kingquasar

    Jul 29, 2009
    After seeing the new close up pictures, I am even more confident that it's a phase switch. I wasn't completely sure where the clear jumper wires were going before, but now I see that they are in fact criss-crossing the outer terminals.

    And yes, it is simply reversing the polarity of the output, making it "out of phase" with the other pickup and cancelling common frequencies between the two pickups.

    Now why you are hearing a difference when the bridge pickup is soloed, I don't know. You shouldn't. It could be that the volume pot for the neck pickup is not completely grounding out when it's in the "0" position. You can test this by turning down the neck pickup volume pot and tapping one of the pole pieces with a screwdriver. If you hear even the faintest tap, there is signal going through (this wouldn't be uncommon). Even if there is a little signal going through from the neck pickup, you'll hear the effects of the phasing.

    -kQ
     
  8. I agree that's is a phase switch; the toggle switch is just a generic switch, it's the way it's wired that gives any clues.

    The Peavey T-40's have a phase switch, maybe check out some clips or discussion of them.

    I know it shouldn't be possible in theory, but I also hear a change when flipping the phase on a T-40 with just one pickup on.
     
  9. lupien

    lupien

    Aug 17, 2008
    Ottawa, Canada
    Thanks for the help everyone. It all makes sense now. I tried again flipping the switch with the neck pickup off and yes there is a difference but if both pickups are on and I flip the switch there is much more of a difference (which is what really confused me at first)

    Thanks again
     
  10. It's a phase switch. The white/red wires feed the inner poles of the switch-these are your signal wires.
    The inner poles are always connected with one pair of outer poles.
    Flipping the switch changes which pair of outer poles the inners connect to.
    The clear covered jumpers are where the magic lies.
    They route the signals so that in one position, the white pickup wire connects to ground, and the red pickup wire goes to the center lug of the volume pot, via the brown and white wire.
    Flipping the switch reverses this- the white wire now goes to the center lug of the volume pot(via the brown and white wire), and red connects to ground.
    What this means is, with both pickups full on, the sound should be much thinner with the switch in one position versus the other. Not terribly useful. You may want to remove it.
     
  11. lupien

    lupien

    Aug 17, 2008
    Ottawa, Canada
    I agree its not very useful. I only like the sound in 1 position (which I assume is off but I`m not sure honestly)

    I was thinking of removing it but I don't want to put the output jack back in that spot since there is already a new hole in the body for it. Would be pretty weird looking to have a fake output jack...

    Maybe you have some ideas on what I could replace that switch with to get some type of "new sound" from my bass. I have another Jazz so I don't see the point of having 2 basses that sound the same so modding this one is fine by me. I was thinking maybe series/parallel switch but after doing some research I found out it might be a little more work then I can handle (well unless I get good instructions but couldn't find any). Maybe you guys have some ideas I've never heard about (like i`ve never heard of phase switches)

    Thanks
     
  12. Sure, you could rewire it so it's a series/parallel switch instead. I'll see if I can dig up a drawing. Here's one. Ignore the colors- your 'hots' are the red ones, 'grounds' are the white ones. Remove all the wires from the switch and reconnect as shown, don't forget the green jumper in the drawing. Be aware that while in series mode, the neck pickup volume pot becomes the master volume, and the bridge volume pot is non-functional:
    http://www.guitar-mod.com/wiring/j_series.gif
     
  13. Beej

    Beej

    Feb 10, 2007
    Vancouver Island
    I've found more use out of series/parallel switches than phase on my Jazz, however the phase switch can be useful if you do over the top wanky distorted wah-wah solos in a metal context... :D
     
  14. lupien

    lupien

    Aug 17, 2008
    Ottawa, Canada
    Thank dmusic148. That diagram is the easiest to understand I`ve ever seen. I never could understand the ones I found (too complex) so I was scared to try this myself but now it should be a breeze. Time to dust off my soldering gun!
     
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