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Question: pickups too hot after OBP-1 install?

Discussion in 'Pickups & Electronics [BG]' started by dreysgroove, Feb 17, 2005.


  1. dreysgroove

    dreysgroove

    Jan 7, 2005
    Oakland, CA
    Hey there. I poured through the forums to try to find an answer to this question, to no avail.
    I installed an OBP-1 in my Copley CBE 59NT, which has dual MM style pups. I'm very happy with the bass, by the way. The problem is that the pickups are now too hot and distorted. I lowered them all the way, which helped, but can't lower them far enough to completely eliminate distortion. Is there a way to put a resistor or something in-line to reduce overall pickup hotness? I'm thinking about whipping out the Dremel and routing the pickup pockets deeper, so I can lower them further, but don't know if that's the best solution... does tone degrade if pickups are too far from the strings? Can any electronics gurus offer a better solution?
    Thanks,
    Alex Cordrey
    freelance bassist
    Berkeley, CA
    www.shantytownmusic.com
    www.doublefunkcrunch.com
    www.hayleyvibe.com
     
  2. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    First you need to determine where the distortion is coming from. The distortion may be inside the OBP-1, but it may also be that the OBP-1 is overdriving your amp's input.

    Is the OBP-1 being powered from two 9-volt batteries or just one? If you turn down the volume knob(s) on the bass, does the distortion go away? What amp are you plugging in to? Can you turn down the input gain on your amp? Does the distortion remain or does it go away?
     
  3. adam on bass

    adam on bass Supporting Member

    Feb 4, 2002
    New Braunfels, Texas
    Endorsing Artist: Spector, GK, EMG and D'Addario
    It may be wired incorrectly. I had great distortion in a bass I installed an OBP-1 in. I almost left it that way! Then I swapped a few wires and it worked like a charm. If not that you need to do as suggested before and find it in the chain.
     
  4. dreysgroove

    dreysgroove

    Jan 7, 2005
    Oakland, CA
    Thanks for the response, Bob. I'm running it at 18 volts. Turning down the amp input gain has no affect, it's not being overdriven, and it's the same through my SWR 350 as it is plugged into my mixer -- so I'd say it's definitely coming from the bass. If I turn the bass volume down to about 50%, the distortion seems less, but not gone completely. It also was greatly reduced when I lowered the pickups, but still present. I'm pretty certain it's wired correctly -- 4 pots, 25 K bass and treble, 500K volume and 500K pan. However, the pan pot is very noisy when turned, even after cleaning with tuner cleaner. I just shielded the control cavity with copper, and haven't put the bass back together yet, so that may have some positive effect...?
    Would it help to run it at 9 volts instead of 18? Can that be done?
    These pickups were extremely hot when they were passive, before I installed the preamp, with more gain than my two Tobias basses with 18V Bartolini systems.
    Thanks for your help,
    Alex
     
  5. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    Given what you are saying, I'd have to guess that either the OBP-1 is wired incorrectly or it is fried. An 18-volt preamp will have sufficient headroom for any pickup. I've never seen an 18-volt preamp that couldn't handle the hotest bass signal.

    The 500K volume pot attenuates the signal from the pickups before it gets to the OBP-1. So, turning down the master volume does the same thing as lowering the pickups. It reduces the signal going into the OBP-1. Turning down the volume pot should eliminate the distortion. Since it doesn't, it tells me that there is something wrong with the preamp. This is why I say that either it is wired wrong or the preamp is fried.
     
  6. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    Forgive me for asking this, but are the batteries fresh? You would also have the same problem if the batteries were running out.
     
  7. adam on bass

    adam on bass Supporting Member

    Feb 4, 2002
    New Braunfels, Texas
    Endorsing Artist: Spector, GK, EMG and D'Addario
    exactly.
     
  8. dreysgroove

    dreysgroove

    Jan 7, 2005
    Oakland, CA
    Ok, thanks. I didn't know that the volume knob came before the preamp in the signal chain. Maybe I'm wrong that the distortion was still present if the volume knob was partially down. If the distortion does go away, say with the volume knob at 75%, is there a way to add an electronic component that make it so the volume knob all the way open would give me 75% of the signal I have now? Changing the value of the volume pot, adding one of those teeny tiny pots before or after the volume pot?
    Reminds me of the Spinal Tap exchange: "These amps go to eleven." "Why don't you just put it at 9, then have 10 be one louder?" "These go to eleven." haha

    I'll put it back together and test it out again. Hope it's not a fried preamp!
    Alex
     
  9. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    Yes, I could look at the wiring diagram and with either one or two resistors, it is possible to reduce the signal level from the pickups. I really doubt that this would be necessary given the 18 volt preamp, but it is possible.
     
  10. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    Just looked at the wiring diagram on the Aguilar web site. One resistor added between the blend pot and the volume pot would reduce the signal. The value would probably be somewhere between 100k and 500k since you are using 500k pots.

    However, I would still check everything else first because there is no reason why that preamp shouldn't be able to handle the signal without attenuation.
     
  11. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    like Bob said, I've never had any problem with any pickups being too hot with an 18v preamp - even when they're really close to the strings.

    Don't be insulted when I ask this: but how are your solder joints? Do you have any cold solder joints? If your connections are dull instead of shiny, then that can cause problems like distortion and crackling
     
  12. dreysgroove

    dreysgroove

    Jan 7, 2005
    Oakland, CA
    I'll re-do the solder joints... some are not as shiny as they should be...
    I'm now having tons of noise, this is driving me nuts!
    Thanks again from all of you who made suggestions.
     
  13. Metal Mitch

    Metal Mitch

    Jul 14, 2003
    NJ
    You mentioned having problems with the blend pot, so it would be a good idea to replace it.

    Lowering the pickups to reduce output will change their tone. You want to leave those in the "sweet spot". Adding a resistor to the hot lead is perfectly ok, I've done it on 2 of my basses to prevent pickup loading.
     
  14. I know that on my active preamp there is a small attenuator on the board in the cavity that sets the output level of the preamp. If yours has the same you may just need to turn it down, (it takes a crosspoint screwdriver to turn it)
     
  15. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    aguilar preamps don't have this feature