Re-wiring to get rid of active pre-amp

Discussion in 'Pickups & Electronics [BG]' started by Not The Norm, Jun 27, 2005.

  1. Not The Norm

    Not The Norm

    Jun 27, 2005
    This is my first post on the talkbass site, so....howdy.

    I have a bit of a question regarding my Fender MIM Deluxe Zone. It is a PJ bass, with an active onboard pre-amp. It also has a five knob layout with a master volume, pan, bass, mid, and treble.

    I just replaced the stock pickups with active EMG-PJ's. But now combining the active p/u's with the active pre-amp, it is way too hot. So bad that I wouldn't play it at our gig this weekend. Too much finger noise, too harsh, etc, etc, etc.

    So, I would like to replace the onboard electronics. But the control set that came with the EMG's was a volume-volume-tone setup. I would like to keep the stock configuration on my bass volume-pan-bass-mid-treb.

    I can't imagine this would be very hard, but I cannot find any sources on-line to guide me along. Any ideas on sources? Any diagrams? What value for capacitors for the tone controls? Wouldn't everything be wired in parallel just like the harness that came with the p/u's?

    Also, where should I get my supplies? Do I need to go to a music store or can I just head on down to Radio Shack?

    Thanks for your help!
  2. luknfur


    Jan 14, 2004

    If you're using the stock Fender pots (probably 250K) with those pups - there's probably your source. You might be able to just change the volume to 25k and get by, don't know but they're cheap, easy to replace. Seems I used the standard Bart and Aggie 3 bands as outboards with EMG's so probably just changing the volume would suffice. You've got the stock harness, pull one volume control and replace the stock volume and see what it does.

    Or go to and look up the BQS system. The passive EMG harness is all 25K pots. I can't remember if their preamps are too but I assume they are.

    Radio Shack is not an electronics store, I'm not sure exactly what it is. About all you can there are battery clips, a few switches, a few caps, and cheap piezos. 95% of the employee's don't even know what solder wick is and the few who do will direct you to the closest electronics store.
  3. There's several better places to order your parts, certainly NOT from your local music store. (As much as I'd like to support them)

    For really specific guitar-building stuff, try Stew-Mac They have tons of info there too. Warmoth has parts too but I haven't found as much support info as StewMac (maybe its there but I haven't found it).

    Since I dabble in amps and stuff and all kind of general electronic stuff, I buy my hard-core electronics parts from Mouser but you must know exactly what you want, for the beginner their catalog would be overwhelming. Same way with Digikey But for the best prices in the world on stuff like resistors, capacitors, transistors, etc those two are the best.

    Parts Express has a decent little selection of electronic goodies. Though they are tailored more to the speaker builder, they also have a good tube selection and their catalog is very user-friendly. Prices are reasonable and service is very good. They do have guitar pots and jacks too. They have a decent help section too, though I don't recall if there's a guitar/bass wiring schematic section.

    I'd recommend getting the schematic you want from StewMac's site, then either order from them or Parts Express....

    I also get stuff from my local electronics store (NOT Radio Shack, unless it's urgent, even then you're lucky if they have it) but for a beginner, walking up to the counter in a real electronics store can be intimidating: "I'd like a 25k pot" then the salesman asks:
    "Audio or linear taper sir? 1/4 watt? Carbon or wirewound? Extended shaft? Trim Pot? PC mount or solder lug?"

    Parts Express or StewMac makes it easier, they just call them guitar pots.
  4. fretlessrock

    fretlessrock Supporting Member

    Aug 8, 2002
    What you really need is a preamp with the correct controls that is designed to match your new pickups. You already have a preamp. It was matched with your previous pickups. (as matched as any Fender preamp is with anything I guess). So all of this malarky about 250k pots and such is a waste of time. You have a preamp, just the wrong one. You want the right one. Look over the EMG site and see if they make a preamp to match your pickups. Also look over the wiring diagrams that came with your EMGs. You should get some ideas there.

    You want a 3-band EQ, pan pot, and master volume (which you already have, BTW) but you need it to be compatible with the new pickups. If you wanted to go passive you would not be able to have boost controls or a mid control. AFAIK, the EMG actives are made to work with a passive tone stack. Maybe EMG tech support can recommend a good preamp?

    Have you considered that you just bought the wrong pickups for what you want to do? If you wanted a better sounding bass with 3 band, pan, and master you could have started by upgrading the preamp with something like an Aguilar OBP-3 or a Bart 3-band.

    Last, I don't think that you are going to find a way to add a preamp to the active EMGs and not have them be super hot and give you a lot of finger and fret noise. You are stacking the gain stage of the pickup preamp with the gain stage of the onboard preamp. That isn't going to change just by changing preamps.

  5. Not The Norm

    Not The Norm

    Jun 27, 2005
    Thanks for the help! I have been plodding along, and am making progress. I can be taught!!

    I got the EMG's because I have them in my old Peavey P-type-bass and love the sound. but the Peavey didn't have all the electronics on board, just the volume and tone control, and I used what came with the EMG's. Pretty simple.

    I'm not looking for a boost. I like a darker tone, so usually I just want to be able to roll off the highs a bit (that's really all I did with the old 5 knob set up). I guess I could live with just the one tone control. But, is there a way to wire three passive tone controls? I guess each with it's own capacitor or is it more complicated than that? What determines the tone range that is controled by a pot?

    Yesterday I took the volume control that came with the new pickups and put it in. I also moved the capacitor from the EMG's harness to one of the existing tone controls, and disconnected the other 2. I can't use the EMG tone pot because of the difference in diameter.

    So I now have the pickups running to the existing blend pot, then to the new EMG volume pot, to an existing tone control. It sounds much better, but still not quite there. After reading what you all wrote, I realized that I need to get a 25K blend pot, and a 25K tone pot with the small diameter. Does this sound right?

    BTW, I'm getting pretty dang good at this soldering business!
  6. luknfur


    Jan 14, 2004

    you can use an audio (volume) pot for a tone pot. The stock EMG harness is all 25K audio pots including the tone control. I don't know what the value is in the capacitors you have but you can make the tone as dark as you want through the caps alone becuase they regulate the amount of treble that passes. A higher value yields a bassier tone and you can pretty much block treble if you want. You really need to know the value of the capacitors to know what you're doing cause you may have actually increased the treble by switching capacitors.

    Personally, I prefer two volumes over a blend becuase it gives you a lot more control over tone than a blend and is probably why EMG supplies it. A blend is easier and quicker but less effective although usually more than adequate. 2 volume 1 tone is the most effective 3 tone passive harness and it sounds like all you personally need. You could drop in another tone for seperate control of each pup or simply have a dummie pot.

    Not clear on the pot variations cause all the pot shafts in the stock harness should be the same and all in the EMG harness the same, so either they should all swap out or none of them should. If the pothole is larger than stem diameter, you can simply fill the gap with tubing, tape, whatever.

    Personally I've had no more trouble running active EMG's with an onboard preamp than any other pups. With pups with any kind of top end you're probably going to get noise with treble boosted cause that's where the noise is.