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EMG BQC Ground Loop?

Discussion in 'Pickups & Electronics [BG]' started by Means2nEnd, Jan 29, 2013.

  1. Means2nEnd

    Means2nEnd Supporting Member

    I have a Euro Spector LX4 I have stock active EMG P/J pickups and I have installed an EMG BQC control preamp at 9 volts. The only mod I have done is an active passive switch. The issue I have is when I turn the treble knob all the way down at the end I get that loud whomp and all signal cuts out and it sends a huge signal through the amp almost pushing the cones out of the baskets.

    I did replace the stacked treble/bass pot 3 times all doing the same exact thing. I used standard 50x2 tone pot just like the original one. The only thing different is the active passive switch. I un grounded the switch to see if it was a ground loop there and it still did the same thing only then there was as to be expected a loud pop when switching. Should I lose the switch? I like having it and now there is a hole for it. I even wired up a kill switch instead and it did the same thing with all three stacked pots.

    Only thing I haven’t done and maybe the only solution is to leave the switch in and just disconnect it completely. Any suggestions?
  2. You cannot create a significant ground loop in a bass, and even if you could, it would not cause the problem you have described.

    This sounds like a preamp issue.
  3. Means2nEnd

    Means2nEnd Supporting Member

    Yes you can in a system with active pickups and active preamp. I wired another BQC before with a stacked volume/volume and had an extra ground by accident and burned out 3 stacked volume pots they smoked and the whole bit. This was confirmed by the main guy at EMG.
  4. wcriley


    Apr 5, 2010
    Western PA
    Wow. I didn't know a 9v battery had enough juice to smoke a pot. (That didn't come out right.)
    Are you sure it was a ground loop and not a short circuit?
    Either way, I see some fun experimenting taking place in my basement tonight!
  5. Means2nEnd

    Means2nEnd Supporting Member

    I did have that system in my Thumb at 18 volts when the magic smoke came out. The EMG preamps are easy to install and are modular if you keep them that way there is almost never a problem. The path of the ground is sensitive to say the least. Whenever I do even the slightest mod and there is a way to have a ground loop anywhere or meet at two places and then ground to the jack I seem to have problems.
  6. Rune Bivrin

    Rune Bivrin Supporting Member

    Oct 2, 2006
    Huddinge, Sweden
    A ground loop isn't something that burns components. A ground loop picks up hum, and has nothing to do with your problems.

    What you have is an unfortunate case of short circuit, which involves the ground as one of the connections. Stop doing whatever you're doing and show us the circuit diagram you're trying to realize.
  7. Means2nEnd

    Means2nEnd Supporting Member

    other than standard install as specified by EMG the switching I added is below. The ground from the switch I tried at the jack, on the bass/treble, and also disconnected and always same result. The switch works and does what it should I just get that strange womp and cut out at max treble cut.

    Attached Files:

  8. Means2nEnd

    Means2nEnd Supporting Member

    I also picked this picture up off the Spector thread. I hope I don't bother the OP of it but I was thinking of trying it if I can figure it out. It's a different circuit but I think would function the same and although it's from Spector I believe it's an EMG product.

    Attached Files:

  9. wcriley


    Apr 5, 2010
    Western PA
    OK. That will add even more fun to my after-work experiments!
  10. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    So not an "active-passive" switch, just an EQ bypass switch. The bypass diagram looks fine (use it all the time), but +1 to it not being a "ground loop", that's not what happens.

    The problem has to be on the "hot" side of things, like the + of the battery.
  11. What does being active or passive have to do with anything? The only thing that changes is signal impedance.

    You did not burn out any components because of grounding issues. The only thing you could have done was apply the battery power to the components when the resistance was low enough that the current draw then exceeded the components' capacity for thermal dissipation. Remember that the currents in the signal path are down in the microAmp range, and the peaks are a couple of volts, at maximum. This comes out to only tiny fractions of a watt of thermal dissipation.
  12. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    No you can't, and what you are hearing is not a ground loop.

    All the active parts share the same ground. In a ground loop situation you need two different ground references. This is almost always an AC powered system, and the ground noise you hear is from the power supply. It's always a 60 or 120 (full wave rectified) cycle hum. Battery powered systems don't tend to create ground loops.

    A real ground loop is what you get when you plug the DI from your amp (on one ground circuit) into the PA system (on a different ground circuit). Under some situations you will hear a loud constant 60 or 120 Hz hum, usually through the PA. That's a ground loop. Almost all DI's have a ground life switch to separate the two grounds. That breaks the loop. Do you see how your bass does not have two separate grounds? It has a single ground point at the output jack. It doesn't matter how many connections are made to that ground point in the bass. Printed circuit boards are the same way, and they don't get ground loops.

    What you have there is either a defective preamp, or you have a short somewhere.

    Also, you should not be getting a loud pop. I had a BTC system with a push/pull active passive and I had no pop at all.

    It sounds to me like you may have a defective preamp with a bad coupling cap which is passive DC voltage to the output. This is known as DC offset, and will cause a loud thump, and sometimes scratchy sounding volume controls, if they are after the preamp, which in this case it is not.

    I'd contact EMG for a replacement.
  13. +1.

    The burned out pots are a clear sign that there is DC in the circuit.

    As a side note, at 9V, a 2W pot does not exceed its capacity for thermal dissipation until around 40 Ohms.
  14. Means2nEnd

    Means2nEnd Supporting Member

    The Thumb bass that fried and my Spector with the cut out on the treble pot are two completely different situations. I can’t throw technical terms around like you guys but I had the grounds meeting in different places along the path to the main ground and then two wires going to the main ground in the Thumb. That’s when the stacked volume pot kept frying. The back track of 9 volts sounds like that’s what happened there like the guy mentioned above. I can tell you I rewired it with only one ground and a new volume pot and it worked fine. It was the multiple grounds that caused it. Not a ground loop I get that but a back track of current.

    My Spector is working fine but shuts down by the treble knob being completely cut. That’s the only issue at hand. I thought it could be from the switch but yeh it’s probably the pre amp is bad.
  15. Means2nEnd

    Means2nEnd Supporting Member

    Can anyone tell me the schematic or drawl it out from the picture in post #8 That would be awesome....:) For the kill switch.
  16. 1958Bassman


    Oct 20, 2007
    You'll change your thoughts on how much energy is stored in a 9V battery if you ever put one in your pocket along with a bunch of spare change. Also, survival guides recommend keeping 9V batteries and steel wool in the kit for starting fires- it works extremely well. Don't test this near flammables.
  17. wcriley


    Apr 5, 2010
    Western PA
    My wife ALWAYS has a fire extinquisher, bandages and phone handy when I'm "experimenting" in the basement. :D