Modulus Quantum 5 - lack of tone

Discussion in 'Basses [BG]' started by emandell, Jun 21, 2005.

  1. I've got a modulus quantum 5 string and I'm not sure that the pre-amp (aguilar OBP3) is working properly, if I set the controls flat there's very little output from the bass at all

    It seems that the only way that I can get reasonable sound out of this bass is to turn the bass/mid/treble almost all the way up to the max, but then what happens is I get a huge amount of bass, the bass frequencies output seems to be huge or nothing with no in-between. The treble and mid dont seem to do much until they are nearly maxed out either

    Anyone any ideas? (I've checked the batteries)
  2. pickles

    pickles Supporting Member

    Mar 23, 2000
    Ventura, CA
    Something is off, I'd get it checked out by a tech. Could be somebody rewired it with the wrong resistance value pots. If you plug another bass into the same amp everything is fine, right?
  3. emandell,
    I did a real dumb thing about 2 weeks ago. I opened up my Spector Euro 4, replaced the battery and looked at the pre-amp - I was curoius what kind it was - it's a Spector TonePump. I put the cover back and plugged it in and no-go. I heard nothing at all. I opened it back up again and one of the wires from the nine volt battery clip broke off. Went to Radio Shack to buy some more and soldered it on with some shrink tubing . . . no problem. Everything works now . . I'd take cover off and take a reall good luck under the hood to amke sure nothings amiss . . .

    Mark F. Sanderson
  4. another bass in the same amp works fine, I've also checked for obvious loose wires
  5. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    How long have you had the bass? Did this problem just suddenly start? What kind of pickups does it have?

    My guess is that the problem is not with the preamp, but that the preamp isn't getting enough output from the pickups...

  6. The only other thing that I can think of is a bad instrument cable . . .

  7. Its never really been right since new (about 6 months ago), cant be the cable, the same cable on other basses works fine
  8. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    To my ears, the OBP-3 can sound kinda bad with too much cut or boost. It's also a zero-gain preamp, which means that if the pickups themselves are not very hot, the preamp itself does not give the option to add any more gain. What kind of pickups are in it? Did it sound this bad when you played it in the store? (I sure wouldn't have brought something home that I was so unhappy with...)

  9. popinfresh


    Dec 23, 2004
    Melbourne, Aus
    Ummm, isn't that an active bass?

    Did you replace the battery?
  10. BruceWane


    Oct 31, 2002
    Houston, TX
    What kind of pickups does it have? If they're EMG's, there's 2 things to keep in mind.....

    1. EMG's are active pickups. They must be powered. Each pickup has a red wire that must be hooked up to the battery to work properly.

    2. Because they're active, they have much weaker magnets than most pickups. So you can set them up a lot closer to your strings without any ill effects.

    So make sure that the pickups are properly wired, and that they're not sitting too far away from your strings.

    Also, is it a 2 pickup model or a Sweetspot? If it's a 2 pickup model, is the problem any better or worse if you solo either pickup? If the output goes up significantly with either pickup soloed, the pickups are probably wired out of phase.

    Also....what kind of pots are in it? Since you've got EMG's with an Aguilar pre, the volume and blend pots should be 25K, tone pots should be 50K.
  11. they're Bartolinis
  12. Mike, thats the problem with buying a bass on ebay

    I've checked the batteries, they're both fine

    I was thinking maybe I should try disconnecting one of the batteries, if I then get nothing at all from the bass that would imply that I'm only getting 9 volts wouldnt it?
  13. BruceWane


    Oct 31, 2002
    Houston, TX
    Nope. The batteries are connected in series in order to get an 18v total. If you take out one battery, you'll get 0 volts. You can take out one battery and get 9 volts into the system IF you put a jumper of some sort between the + and - terminals of the empty battery clip.
  14. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    Was it new or used? If it's new, the pots and everything should be correct, since the OBP-3 is an option from Modulus. If it's used, however, the preamp may be a later add-on, and there's no telling what kind of screwiness might have been done to the wiring. So here are a couple of thoughts:

    1) BruceWane had a good point, that it's possible the pickups are wired out of phase with each other--that would certainly give the result you're describing, when both pickups are on full. Do you hear the same thing when you pan the blend all the way to the bridge or the neck pickup?

    2) There is no difference at all in gain between 9v and 18v on the OBP-3, so pulling one battery out of the circuit doesn't really tell you anything.

    3) Just to be sure, you might check the Aguilar wiring diagrams at

    It's a pain to do, but it would at least give you an idea if the thing is badly wired.

    4) If you're feeling really ambitious, you might pull one of the pickups and see what Bart model they are. At least a couple of the Barts are active and require their own 9v connection, and some others are specifically low-output and designed to be used with the Bart preamp circuit that provides extra gain.

    FWIW, I've bought a lot more high-end stuff online or from Ebay than in person from a store...

  15. BruceWane


    Oct 31, 2002
    Houston, TX
    BTW, since you've got barts, and almost all barts are passive pickups, you could completely bypass the preamp by running the pickup output straight to the jack. It's very unlikely that both your pickups have problems, though. It's probably a wiring problem, a bad potentiometer, or an incorrect value potentiometer. Most preamps are pretty bullet-proof; they're not going to burn up if somebody touched the wrong wire to a battery.

    Really, first thing I would do is look over the wiring and make sure it's all done correctly.

    You can get OBP-3 wiring diagrams at Aguilars website.....

    OBP-3 Schematics
  16. thanks for your help guys, but its off to the bass gallery for this one.

    Its just as bad with either of the pickups on their own, I cant see anything wrong with the wiring, the bass was supossedly new old stock, and the wiring looks clean enough to be factory.

    I cant hear any effect from the treble control at all and the bass and middle only seem to do anything in the last 25% of their travel. The bass control is either full on or nothing

    I tried disconnecting the batteries, like you said disconnect either one and its dead. Both batteries are new
    I'll post the outcome
  17. update - I was advised that the pre-amp is working as it should, I also played another bass (different brand) with the Aguilar OBP3 and saw the same thing, (admittedly slightly better) on a different amp

    So, I just dont like the Aguilar circuit, I got them to swap it to a Retro something-or-other and its now completely a different beast, the bass control has a huge amount of effect, parametric mid (need to get my head round that) and a treble control that does a bit more than add hiss

    Thanks for your help

  18. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    Cool! I'm not really sold on the OBP-3 myself, and it's definately interesting to hear the experience of someone who's swapped theirs out for something else.

  19. vene-nemesis

    vene-nemesis Banned

    Jul 17, 2003
    Bilbao España
    Funny thing, jerzy drozd uses the OBP-1/3 as stock preamps and his basses do have huge output, and do make the cut boost trick right. I would suggest to highjack the preamp an run the pickups and the batteries straight to the output jack to check if they are working right.