Jaguar Bass preamp mod

Discussion in 'Basses [BG]' started by johnk_10, Oct 8, 2010.


  1. johnk_10

    johnk_10 vintage bass nut Supporting Member

    Joined:
    Feb 16, 2008
    Location:
    Thousand Oaks, CA
    Disclosures:
    John K Custom Basses
    after installing some DiMarzio ultrajazz pickups in my Jag a couple of months ago, and not being extremely thrilled with the Jag's kinda loose, and boom/sizzle stock preamp (treble and bass controls) i just modded mine by installing an EMG BTS system in it. the EMG's treble and bass controls have center detents (as a reference to flat), 4 selectable treble frequencies, a better bass boost/cut frequency as well as a cleaner, more punchy circuit. (the fender circuit was just about all boost).

    i didn't want to route or modify the body in any way, so in order to use the jag's stock thumb wheels, i had to order some 50K linear pots with a shorter threaded mounting shaft that still had a center detent.
    here's a pic of the EMG pots:

    [​IMG]

    here's the new pot as compared to the EMG one:

    [​IMG]

    i also had to bend the 5 pin connector 90 degrees so it would fit underneath the switch in the upper control plate cavity.

    here's a pic of the new (bass control) pot wired to the EMG's main pcb:

    [​IMG]

    here's a pic of the new treble pot (left) and EMG treble pot mounted to it's pcb:

    [​IMG]

    and here's a pic of the new treble pot wired to the pcb:

    [​IMG]

    i used very thick 3M heavy duty clear double stick tape to mount the main pcb in the cavity, and the small one on the control plate:

    [​IMG]

    and finally, i used the old preamp's cavity under the pickguard to add another 9V battery in series to the original one, so the system runs on 18V for better performance and maximum headroom:

    [​IMG]


    the test results:
    well, first i had to reverse the outer wires on the new pots since the controls worked backwards (easy one minute fix).

    once i got them running the same way as the original controls, i gave it a listen. this preamp is TONS better. it's still completely bypassable (with the switch on the upper control plate), but i actually prefer to always leave it on. in the center detents, the tone does not change, but a very slight rise in gain occurs, i suppose due to the buffering. when you roll the volume down, it's tone stays pretty much the same in any position (the highs don't roll off near as much as in the passive mode).

    the dimarzio ultrajazz bass pickups in this bass sound great and are extremely quiet. when the preamp is kicked in, there is no additional hum, but there is a very slight amount of hiss added, which is normal for any preamp that is buffering/boosting signal and frequencies, and is much quieter than the fender preamp that it replaced.

    i have an EMG VMC (variable midrange control) on its way to me and i'm going to experiment with replacing the jag's passive master tone with the EMG's mid control. it has concentric pot (freq on the ring and center detent boost cut on the upper) so i also ordered the fender stacked knob kit that looks like a regular jazz bass non-stacked knob (not a conventional jazz bass stack knob) fo it.

    i'm generally a passive bass guy, but after using my EMG JV/TBC jazz bass at the last gig, and loving it, i thought it might be cool to have treble, sweepable mids, and bass controls all on board at least one of my fender basses. i mean, the way i see it, i might as well take advantage of all the knobs and switches that they put on that thing. ;)
  2. Spleenface92

    Spleenface92

    Joined:
    Aug 13, 2009
    Location:
    Manchester, Connecticut
    I understood literally none of that except for the fact that it's awesome.
  3. johnk_10

    johnk_10 vintage bass nut Supporting Member

    Joined:
    Feb 16, 2008
    Location:
    Thousand Oaks, CA
    Disclosures:
    John K Custom Basses
    :)

    it's pretty simple. basically the EMG system wouldn't fit unless you either route the body for it, or change the pots to some that will fit and wire them remotely. i did the latter.
  4. johnk_10

    johnk_10 vintage bass nut Supporting Member

    Joined:
    Feb 16, 2008
    Location:
    Thousand Oaks, CA
    Disclosures:
    John K Custom Basses
    been tweaking the new tone control preamp a little bit more.

    trying to get it to be as invisible as possible with the bass and treble controls in their center detents ( i.e. zero gain boost, or eq change) and i believe that i acheived it. the preamp is after the (passive) master volume & tone controls, so rolling either one down has no effect on the hiss whatsoever. the EMG BTS was a little brighter and about 1 1/2-2db louder when switched in, so i added an .022uf cap to ground as well as a 15K resistor on the output of the preamp. now there is no difference in volume whatsoever, and the hiss (at around 8-10Khz) was reduced by more than 75%. it still sounds transparent and can get too bright if i crank the treble (just as it was before), but this way, it sounds and feels much more natural. i was looking for no volume boost so that when on stage it wouldn't be too 'hyped' when clicked in, and for me, it is perfect this way.
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  6. Reynoldbot

    Reynoldbot

    Joined:
    Dec 20, 2009
    Location:
    Minneapolis, MN
    I too really hated the stock preamp for the Jaguar, and had it switched out for the Aguilar OBP-2. Like yours, it is now boost/cut with a center detent, and like yours it sounds fantastic.

    Unlike yours my preamp is still 9v, but really when I turn the bass and treble boost all the way up it sounds absolutely bonkers, so I'm not too worried about headroom. I usually keep the active on but with only slight boost on the treble and slightly more on the bass. As expected the OBP-2 pairs really well with my Aguilar pups, and I get a real thumpy vintage tone out of my Jag.
  7. Spleenface92

    Spleenface92

    Joined:
    Aug 13, 2009
    Location:
    Manchester, Connecticut
    Ah. Speaking of not fitting, I had to relocate the two Orange Drop caps for my jaguar (rewired in a passive JJ setup). One's where the old pre used to be and the other one is in the battery box rout.
  8. johnk_10

    johnk_10 vintage bass nut Supporting Member

    Joined:
    Feb 16, 2008
    Location:
    Thousand Oaks, CA
    Disclosures:
    John K Custom Basses
    IMO, there's really no need to use orange drops (i never do), there are alot better sounding caps that are ALOT smaller. i use vintage fender cornell-dubilier .047uf ceramic discs that are flat and about the size and thickness of a dime.
  9. Spleenface92

    Spleenface92

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    Aug 13, 2009
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    Manchester, Connecticut
    So why's everyone here all bonkers about them?
  10. johnk_10

    johnk_10 vintage bass nut Supporting Member

    Joined:
    Feb 16, 2008
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    you got me. i always thought they were ho-hum. :confused:
  11. darthplagis

    darthplagis

    Joined:
    Feb 8, 2006
    Location:
    newcastle upon tyne (UK)
    i love the mod, id want to keep the passive option and im glad that you have found a way to do it...... damn looks like im buying a new pre for my jag in a few months :ninja:

    i do love the SD basslines stacked vintage, that i have in my jag so that would be a total pimp out.
  12. Jim C

    Jim C Supporting Member

    Joined:
    Nov 29, 2008
    Great R&D and a very tidy install.
    Will be interesting to hear how the variable mids pre works with this set up.
  13. Volume4

    Volume4

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    Sep 15, 2009
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    Long Island
    +1
  14. WoodyG3

    WoodyG3 Supporting Member

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    Location:
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    Good use of the former preamp cavity for an extra battery. I would agree that the weakest link in the bass is probably the preamp, so this was an interesting mod to me. You certainly keep things tidy, super pro job! How much do you figure you spent in making this swap?
  15. johnk_10

    johnk_10 vintage bass nut Supporting Member

    Joined:
    Feb 16, 2008
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    Thousand Oaks, CA
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    John K Custom Basses
    the BTS preamp cost me $79 shipped, and the two 50K linear center detent pots ran $1.65 each + about $5.00 shipping, sounder $100. ( i bought two extras. if you need them let me know).

    since i'm really happy with the mod, i have since cleaned up the wiring a little more, and decided to remove the 15K resistor but keep the .022uf cap to reduce the hiss an overall brightness when set flat (in the detent positions).

    here's a pic of it as it is now:

    [​IMG]
  16. UnfortunateTony

    UnfortunateTony

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    Jul 26, 2010
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    Seattle
    Goodness gracious *fans self*
  17. darthplagis

    darthplagis

    Joined:
    Feb 8, 2006
    Location:
    newcastle upon tyne (UK)
    just a quick Q, as you obviously covered my question while doing this mod.

    the active/passive switch, is it just a post passive switch that passes the signal either to the output or the pre?

    i have asked in the pickup section but it gets samped by what is the best J aftermarket threads and will this P pickup work in my squire threads :ninja:

    i have a spare yamaha EQ (from a 90's BBg5a) that i could pop in my jag if i could figure out the switch.
  18. johnk_10

    johnk_10 vintage bass nut Supporting Member

    Joined:
    Feb 16, 2008
    Location:
    Thousand Oaks, CA
    Disclosures:
    John K Custom Basses
    the switch is just a DPDT (double pole double throw).
    if you wire it like this, you'll have passive in one mode and active in the other. this is a true bypass (which, IMO, is better), since the jag's stock wiring isn't.

    [​IMG]
  19. darthplagis

    darthplagis

    Joined:
    Feb 8, 2006
    Location:
    newcastle upon tyne (UK)
    ah sweet thanks johnk,

    another Q :) with the scematic above the volume and tone still work as in passive its just before the pre right? or is it just a switch between two modes with independant controls?

    i am in the process of wiring up an artec 3 band that i had lying about into the jag, so far i have popped the passive controls to the roller wheels and then im in the middle of extending a few wires for the eq pots so i have a concentric treble and bass with a separate mid eq on the rotary controls......... ill let people know if i have failed miserably or not in a few hours :ninja:
  20. darkstorm

    darkstorm

    Joined:
    Oct 13, 2009
    Very nice mod & upgrade and very nice mod work to, on your jag.
  21. johnk_10

    johnk_10 vintage bass nut Supporting Member

    Joined:
    Feb 16, 2008
    Location:
    Thousand Oaks, CA
    Disclosures:
    John K Custom Basses
    the volume and tone controls work in both the passive and active modes, exactly like the original jag bass does.

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