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Here's a wierd one for you all

Discussion in 'Pickups & Electronics [BG]' started by Funky Doctor, Oct 3, 2005.


  1. Funky Doctor

    Funky Doctor

    Aug 28, 2003
    Australia
    I have 2 single coil pickups in a bass of mine with an aguilar preamp. Now, the way I have the blend pot wired up is the same as the way aguilar suggests in their wiring diagrams. The only difference is I have no connection to ground on the blend itself. The sound is fantastic but in certain places I get buz. I can cope with it mostly, because it isn't overly loud. Now, when that earth connection is made from the blend pot, something wierd happens. The blend works in a funny way. There is no sound whatsoever in when the beldn is in the middle, ie, at the centre detent. Favouring one pickup slightly to get smoe sound results in basically soloing it. It's really wierd. On the up side, there is no noise at all tlike this, but yeah, i essentially have a pickup switch. Anyone know what might be going on here? I have tried many things like swapping the pase of one pickup, 2 volume pots, and a few more, but it's always the same.
     
  2. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    if you replaced the blend with two volumes and got a similar response, my guess is something's screwed in the wiring or (less likely) the preamp itself. At least that's where I'd look.

    But that sounds (at least in part) like an out of phase response. I'd also check to make sure the jack is wired correctly. Those flush mounts can be hard to tell the tip from the neutral and easy to have contact between them.
     
  3. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    Since you can get a full sound, just not the sound you're expecting, I'd say it's not the preamp. The obp-3 doesn't really care whether it's got a blend pot, 2 volume pots or wired stright to a pickup in front of it.

    It sounds like you have the blend pot wired incorrectly, I'm not entirely clear from what you wrote what you did when trying out using two volume pots.
    Can you describe EXACTLY what you did, and take pictures of the wiring?
     
  4. Funky Doctor

    Funky Doctor

    Aug 28, 2003
    Australia
    I think I would have to agree with you david, that it isn't the preamp. I will have to get around to taking some photos, but I'm pretty sure I have wired it all up correctly. I have gone though and checked the wiring countless times against the aguilar wiring diagram. One thing I should mention though, the pickups have 3 wires. 2 of them are obviously the output but the third seems to be just a shield or something, as it's pretty much an open circuit between it and any of the other wires. I have grounded these wires from each pickup. I'm quite stumped...
     
  5. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    One wire is hot, one is ground and other wire is shield ground.
    You should only have one wire from each pickup going into the blend pot.
     
  6. Funky Doctor

    Funky Doctor

    Aug 28, 2003
    Australia
    Yep yep, one wire going ti blend pot, the other 2 to ground.
     
  7. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    Sinlge coil jazz pups and they have 3 leads? That to me says active. Have you ran a meter to verify start and finish? Is one of them red?

    You may have a set of active jazz pups and you're trying to wire them passively.
     
  8. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    I would also check to see if any of the lugs on the blend pot are grounded. This sounds like an improperly placed ground.
     
  9. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    While that's certainly a possibility, I've seen single coil J's with a shield ground wire also.
     
  10. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Yep, me too (I think?) but that is the more the exception and not the rule from the pups I've had.

    But it seems something is either being overlooked or is atypical here. I've never tried to wire active pups passively so I don't know what the response would be. Or even if they'd get enough juice through such wiring to have any output. But it's a possibility to my knowledge (especially with so many posts on TB regarding confusion over what an active pickup is) and therefore an aspect to rule out one way or the other.
     
  11. Funky Doctor

    Funky Doctor

    Aug 28, 2003
    Australia
    Were there any Lane Poor six string pickups that were made active? It's almost definitely a shield wire since if I leave it out, ie, don't hook it up anywhere, it makes no difference. Active pickups have a tendency to not work without power.
     
  12. That's weird. Don't see how you could get what you're describing, no signal when pot at center position, but signal on either side.


    You can hook it up passive and see if the same thing happens. I imagine it should. All the blending and volume take place totally independently of the preamp circuits.

    First though, make sure the blend pot is hooked up right.
    Pot terminals are 2 groups of 3 leads.

    a d
    b e
    c f

    Hot lead of pickups go to terminals b and e respectively, one pickup to b, the other to e.

    a an f are connected together.

    c and d are connected together.

    One of the pairs (a and f ) or (c and d) go to ground, the other goes to top of volume pot. Pick one pair, doesn't matter which, lets say a and f, connect them to ground. c and d go to top lead of volume pot. Opposite is fine too.

    Then connect bottom lead of volume pot to ground. center of volume pot goes to preamp.

    If you want to wire it passive, take the center tap of volume pot go straight to the output jack, tip connector instead of to the preamp.

    I'm guessing you'll see the same behavior.

    Preamp is now out of circuit, volume and blend are hooked up same as before. I'm thinking you've got it hooked up weird, must be a mistake somewhere.

    Is that the normal way to hook up a blend pot? Anybody know? I'd think you could use a single pot, not a dual, just hook hot lead from each pickup to the outside terminals, then pick the blended signal off the center tap. That'd be my first guess how to hook that up. You wouldn't need a dual pot to blend pickups either. [edit]Forget that, just pulled the plate off my Ken Smith and it looks like a dual pot for the blend.

    Randy
     
  13. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    Didn't realize these were LP's. To my knowledge there are no active LP's. I've got an LP M3.5W which is 2 lead with bare ground.

    I would concur the next step would be to skip the preamp and run the pups passive through the volume/blend/jack. If you get the same result, you can basically rule out the preamp.

    The pups would cancel one and other at the blend detent however if the pups were out of phase - but you said you swapped the leads to one pup and it made no difference and that would resolve an out of phase issue.
     
  14. Actually you can already rule out the preamp, I looked at the circuit diagram, and the pickups go to the blend pots, then the blended output goes to the volume pot, the output of the volume pot finally then goes to the input of the preamp. The signal is already blended or not by the time the preamp gets hold of it. Pickups/blend pot are not even connected to the preamp at all. Only thing the preamp is aware of is the volume pot output.

    Randy
     
  15. scoote3639

    scoote3639

    Mar 16, 2004
    34952
    every one here is correct in their assumptions but,having gone throgh this myself a number of times, i have the solution.the aguilar schematics ARE correct...but only with the blend pot that they sell. if you dont have that specific piece but another ...say an allparts piece then switch the hot and ground.
     
  16. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Maybe but he said he used two volumes and got the same results. Looks like Randy is accurate as Aggie doesn't have a lead to the blend like a Bart does. So it SHOULD behave the same ran passive. But I would wire it passive regardless and verify that.
     
  17. Agreed, that will show if the pots are a) wired correctly or b) somehow defective, or c) it works as it should...

    Randy

    The wiring to the pots on the aggie schematic look like they're hooked up to standard pots, and actually I'm not sure how aggie's pots would be different requiring you to switch hot and ground.... Looks like swapping hot and ground would only reverse which pickup you choos, from clockwise is bridge, counterclockwise is neck to the other way around, if I remember right from seeing it last night.
     
  18. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    I've never heard any comments regarding an issue with a blend in an Aggie. EMG's have that funky thing that's for thier system preamps only but that's the only one I'm aware of. There are some variations like active blends but to my knowlege, a passive blend is a passive blend and is not particular about who it's wired to. I installed my OBP-3 as an outboard so I had no blend to dink with.

    Blends can be a pain with the cross overs and close quarters and all but two volumes responding the same would have ruled out anything to do with the blend from what I know.

    Regardless, the thing to do is to eliminate what's not the problem till you get down to what is. And wiring to just the volume, blend (or two volumes), and jack is pretty much getting down to either the harness, the pups, or the way it's wired.
     
  19. I was responding to the guy that said aggie uses 'special' blend pots. I've never seen a pot that wasn't the standard 3 connection (top, wiper, bottom)... AFAIK, they don't make any other configuration. That's what a pot is, resistor with moveable arm to vary the resistance.
     
  20. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Yeh, my screw up. Must have hit the quote instead of the post reply. It's always sumpthin.