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Problem with EMG and Aguilar preamp

Discussion in 'Pickups & Electronics [BG]' started by twscrb, Aug 18, 2004.


  1. twscrb

    twscrb

    Aug 17, 2004
    I had an Aguilar OBP-3 installed to go with my EMG-J set.
    I'm running the system at 9 volts. It sounds awesome but when I sweep the volume pot, at some point during this motion the bass makes a 'scratching' sound as though the pots are dirty. The pots have been cleaned and changed but still the same problem. At the same time I can see my speakers move briefly as though they're receiving a voltage spike. The preamp was returned to Aguilar and they said that there is nothing wrong with it. The pickups worked fine before I installed the preamp. I'd like to know if anybody has had luck with this combination; or just let me know what we're doing wrong.
     
  2. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    I ran an OBP-3 as an outboard through lots of pups - and more likely than not, EMG J's. I'd have to read back through my own reviews. Never had a problem with the Aggie or any of the preamps with any pups, that I can recall anyway.

    The OBP-3 is designed to run as an 18V system and that's how I ran it. But I did run an OBP-1 as both an onboard and outbaord with only a 9v and it's recommended 18v. Often the extra 9v is just for head room but I'd try 18V for kicks and grins and see what gives before looking for problems elsewhere, since that's what their diagrams show. I doubt it will alter anything but it's a quick and easy check so what the hell.
     
  3. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Upon further thought (I run pups direct now so don't mess with this stuff much anymore):

    If you've got solid grounds and connections that leaves improper installation, faulty component, and and incompatibility. I'd all but rule out incompatibility.

    I'd replace the battery even if it's new. Check the jack connections for sure. Try another cord. And you should have a 25k volume pot in the bass and 50K linear tone pots.

    I assume you've isolated the problem to be in your bass to begin with.
    If not, I'd also run another bass to your rig to make sure your bass is the problem and not something else.
     
  4. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    I've run obp-3's at 9v with no issues. As people have said, double check your connections - make sure there's no cold solder joints etc.
     
  5. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Also, if you've got a shielded cavity a common problem is a hot lead grounding out - often against the wall or below the lugs.

    If you don't have a shielded cavity you've probably got shielding to the back of the cavity cover - a hot lead contacting could pose a problem as well.

    And, as David mentioned, cold joints especially grounds to pot backs. The connections ideally should look like clean silver not pewter. Poor grounds were by far the most common problem I had in harnesses. To avoid excessive heating to pots in general (as well as to get around soldering to blend and dual concentric pots), I ended up eliminating wired pot to pot grounds and running shielding strips on the bay floor from pot to pot. A few times I had to run a ground from the back of the volume pot only with strips to the other pots. You can run a continuity check with a meter to double check pot to pot grounds, or most any connection for that matter.
     
  6. JOME77

    JOME77 Supporting Member

    Aug 18, 2002
    Georgia
    Hard to trouble check via the internet but I'd do the following:

    1) verify that you didn't connect the bridge Ground to the electronics (not required for EMG and could cause some intermittent problems).
    2) make sure that all components (pots, switches and jack are ground straped
    3) verify when the output jack is plugged into the bass that the jack doesn't come close to the cavity shielding or other grounding device.
     
  7. twscrb

    twscrb

    Aug 17, 2004
    Thanks for all of your responses. I've tried everything that's been suggested including changing the pots, using 18 volts, removing all shielding, etc.
    I've tried placing the pickups on lug #2 and then lug #1 but still the same problem.
    My OBP-3 has an active/passive switch.
    The basic wiring scheme that I'm using is lugs #1 on both pots go to the hot lead of the output jack, lugs #2 go to the pickups, and lugs #3 go to the active/passive switch.
    If anybody has this same setup working please let me know.
    And any other ideas would be appreciated as well.
     
  8. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    I had an OBP-3 wired to two EMG-J pickups, and had none of the issues you describe.
    I've also wired up a bunch of obp-3 preamps in other basses, for myself and for friends, with/without active/passive switches and never had this.

    I honestly don't think it's anything to do with the preamp, I'm sure it's something in the wiring/grounding of your vol pots and switch.

    Did you check for cold solder joints? With the noise you describe, does it happen with both vol pots or only one? If only one, it could point to a problem with that pot.

    You also say you have both vol pots output wired into the active/passive switch? Those lugs can be small, and tricky to get two wires in there cleanly.

    Have you tried wiring a through output wire. i.e. the output from pot 1 goes through the output from pot 2 to the active/passive switch input.
     
  9. twscrb

    twscrb

    Aug 17, 2004
    It sounds like you've done similar installs.
    Is it possible for you to give me a quick idea about your wiring scheme. I've tried several different ways but same problem. I can hear the sound from either volume pot. And I've also tried it with lug #3 of both pots conneted to each other and then to the active/passive switch. For my setup I have the two 25k pots for the volume pots plus the bass, mid, treble pots from the OBP-3. I basically would like to know how you wired your lugs on the pots from the pickups, active/passive switch, and output jack.
    I've done so many other installs without a problem but this one just won't budge. And I know that it's probably something really simple that's wrong.

    Thanks
     
  10. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    Just usual vol wiring - vol lug #1 goes to ground, pickup hot goes to #2 and output comes from #3.

    How are you grounding the pots themselves?
     
  11. twscrb

    twscrb

    Aug 17, 2004
    The wiring of my volume pots is like this:
    Neck pickup:
    Lug #1 to ground on output jack
    Lug #2 - - pickup braid on back of pot; core on lug #2
    Lug #3 - - wired to lug #3 to lug #3 on bridge pickup

    Bridge pickup:
    Lug #1 to ground on output jack
    Lug #2 - - pickup braid on back of pot; core on lug #2
    Lug #3 - - wired to active/passive switch
     
  12. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    ok, but my question was more how are you physically grounding the pots.

    e.g. are you shielding tape in the cavity and joining that to jack ground, or running a ground wire from the pot to a star ground, or connecting the back of each pot using a ground wire and joining that to a jack or star ground?
     
  13. twscrb

    twscrb

    Aug 17, 2004

    For the gound, I'm actually running a wire from lug #1 of each pickup pot to ground on the input jack - - not in series, parallel.
     
  14. luknfur

    luknfur

    Jan 14, 2004
    DIXIE

    FWIW:


    For many reasons, the jack is among the most common source of problems in a bass harness and the more wires running to it the greater that probability is enhanced. A jack is a moving (often twisting) component which is prime for wire breaks and shorts. You can check for continuity from the ground lug to each pot back. Personally, I'd have had one volume and one ground going to the jack. Every inch and added wire simply increases probability of malfunction. When they're crowded into tight space or added to a moveable part it's enhanced.

    Ideally, wiring should be as minimal and simple as possible.

    Out of curiosity, are the ground wires bare or shielded?

    Also FWIW, previous references to shielding were not directed towards removing it once it's installed. You can simply throw a piece of electrical tape down at problem areas (ie, below pot lugs, between lugs and bay walls, wherever) and leave the sheilding intact. At least that's what I did.