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Replacement preamp for Fender Jazz24

Discussion in 'Pickups & Electronics [BG]' started by Troph, Jan 9, 2014.

  1. Troph

    Troph Supporting Member

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    Has anyone here been happy with a preamp used to replace the stock Jazz24 unit? The one I have is pretty awful, and it seemed to get worse. When I first acquired the bass, I don't remember it being so muddy, but now I can't seem to get useful tones out of it.

    The stock pickups are some type of Seymour Duncan passive unit, and I assume they're worth keeping. But the preamp in these things was known to be failure prone, so it may be worth replacing I guess.

    I was looking at a Bartolini NTMB using the "4 knob, 1 Switch" configuration, or maybe an Audere Classic module? (Not sure whether the "pro-Z" switch is worth it.)

    Not sure whether it will be worth it regardless, frankly. I already dumped money into the neck (had it PLEK'd) because the frets weren't very good out of the factory, but I haven't been playing it much because I've also been unhappy with the electronics. Now I'm looking at dumping more $$ into the electronics, with no guarantee I will be happy with the result.

    Such is the modification risk, I suppose. :)
  2. mcnach

    mcnach

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    John East J-Retro preamp. Without hesitation. :)
  3. MIMike

    MIMike

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    I solved the preamp problem by removing the whole thing. My Bartolini's are wired to a 3way switch, then directly to the jack. No vol. no tone. Just the Bart's.

    Attached Files:

  4. Troph

    Troph Supporting Member

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    Heh, interesting. Well, as I already have several passive Jazz basses, I'm thinking I'll keep this one active.

    Hmm, well the J-Retro appears to be a pre-built replacement control plate, which would drop into most Jazz basses, but I don't think it will fit the Jazz 24 because this particular bass doesn't have a control plate...

    The John East U-Retro Deluxe is an option, but wowzer is it ever expensive... $325! That's a bit hard to justify on a bass that was about $400 new. Does it play songs for me? :)
  5. walterw

    walterw Supportive Fender Gold Supporting Member

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    i've fixed several of these when their preamps died (put the 9V in backwards and *poof*) using the EMG BTS control; crystal clear (better than before), fits in fine, runs great at 18V, and is like $100.

    i wire the mini-toggle for true-bypass active/passive.
  6. mcnach

    mcnach

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    Oops, you're right, I was not familiar with that model and assumed it was just another Jazz flavour.
    The U Retro will work and I know it sounds expensive, but to me, it's worth it.

    I had a J Retro on a bass that cost me £40 once. The J Retro was £100 (bought it used)... Gigged with it and it was awesome.
  7. LightGroove

    LightGroove

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    Sounds like a winner..can he still use the stock pups or replace those to?
  8. Troph

    Troph Supporting Member

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    Interesting. The "BQC System HZ" model looks like the closest match to keep the 4-knob 3-band layout from the bass, using passive pickups. I don't think I've ever hear anyone else review this preamp specifically.

    http://www.emgpickups.com/accessories/bass-accessories/bass-eq-passive/bqc-system-hz.html#info

    Not sure yet what I'll do with the toggle switch control, which is apparently not usable in the BQC System. Maybe I can rig it to do a passive bypass of some sort.

    I'll give it a try and report back. :)
  9. Troph

    Troph Supporting Member

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    Another option I suppose is that I could go ahead while I'm at it and swap the pups too, and put in some split-coils like DiMarzio Ultra Jazz, and use the unused switch as a series/parallel selector.

    I usually hate changing two variables at a time, though... it's hard to know which mod changed the sound, and how much. :)
  10. MIMike

    MIMike

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    I have a set of old Model J's that are currently in my fretless. I may put those in my JB24. My Bart's that are in in now must be single coils because they hum when soloed. I bought them off Craigslist with the understanding that they were humbucking...I think I got taken (first time that ever happened on a CL deal I bet).
    I really want a clean sound with no hum since I run one pickup or the other to change my tone (now that I don't have volume or tone controls).
  11. Troph

    Troph Supporting Member

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    I also have some Model J's in a fretless J bass. They're so tall relative to traditional jazz pickups that I considered making the pickup cavities deeper to accommodate them, but I didn't because I was in a hurry. Now unfortunately they're too close to the strings and can't be adjusted any lower without some woodwork. Don't know whether or not the Jazz 24 has deeper cavities or they'd need to be hollowed out too.

    Also, in my fretless, the Model J's do pick up some significant EMI hum/buzz, which was surprising to me because they're supposed to be humbucking due to the side-by-side split coil arrangement. However, I haven't had time to work on this bass for quite a while, so the hum could be caused by any of several fixable items:
    - strings being too close to the pickups, causing radiation into the pole pieces
    - the fact that I'm running D'Addario tapewounds, and the inner conductor may not be grounded correctly
    - lack of shielding in general (including the long wiring runs from the pickups to the control plate)

    Anyway, YMMV as always. :)

    I ordered the EMG "BQC System HZ" at an online reseller for about $100, which is a pretty good deal for a complete preamp assembly with all hardware. We'll see how it works!
  12. MIMike

    MIMike

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    My fretless sounds great, but you're right about those pickups, they have that extra magnet on the bottom that make them taller than most.
    I will either try to score some humbucking J's at NAMM later this month, or swap out the model J's from my fretless.
  13. Stumbo

    Stumbo Supporting Member

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  14. walterw

    walterw Supportive Fender Gold Supporting Member

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    no need to change the pickups; also, this "HZ system" is a new one on me.

    just get the BTS control, which is just the preamp itself, no passive volume or pan pots; the bass already has that stuff,no need to buy and install it again.

    as for the toggle switch, you'd wire it like this for true bypass active/passive:

    [​IMG]

    "effects circuitboard" is the BTS control, while "input jack" is the pickups, pan pot and volume control.
  15. Troph

    Troph Supporting Member

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    I went with the "BQC System" just because it actually has a full 3-band EQ with midrange control (and even sweepable mid freq knob). The BTS Control, according to EMG's specs, only has a 2-band (bass/treble) EQ. I typically use the mid control more than I use the others anyway, so I didn't want to lose that.

    As for the "Hz System" vs. "System", apparently the only difference is the blend apparatus. Here is what EMG writes about the difference between the two:
    "The ABC Control is designed for EMG Active Pickups. It allows loss-free balance between two pickups and has a center detent for the middle position. If you are using EMG-HZ Passive pickups, or other passive pickups you will want to use the B125 Active Balance Control which features buffered inputs for passive high impedance pickups."

    So the blend control is not just a simple potentiometer, it actually has some type of active buffer stage. Here is the product link, although there is basically no real information there, sadly:
    http://www.emgpickups.com/bqc-system-hz.html

    Thanks for the passive bypass ideas... I'll look into what changes will be required to bypass everything, including the buffered blend.
  16. datsaxguy

    datsaxguy Supporting Member

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    I put u retro in a 5 string one of these with the stock pups. The bass was the biggest baddest thing I ever played. Just Massive. The neck on the bass wore me out and I regretfully had to sell it. It was worth every penny.
  17. Troph

    Troph Supporting Member

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    What is the selector switch supposed to do on one of these Jazz24 basses, stock? I've heard some people claim it's a preamp bypass, and others claim it's just some kind of "slap switch".

    On mine, the switch alternates between nice and clear in one position, and muddy, mid-heavy, and nasally in the other.

    The EQ controls more or less work in both positions, which leads me to believe it can't be a complete passive bypass. Or can it?

    I guess it doesn't really matter, as I'm now committed to yanking it. :)
  18. walterw

    walterw Supportive Fender Gold Supporting Member

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    i think it's the duncan "slap switch". yes, active both ways.

    as for the true bypass diagram, allow me to throw out line6man's rendering, beautiful as always:
    [​IMG]

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