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Aguilar DB750 mod idea...

Discussion in 'Amps and Cabs [BG]' started by Matt Call, May 13, 2006.

  1. Matt Call

    Matt Call Supporting Member

    Aug 1, 2004
    Minneapolis, MN
    Well... I just can't get rid of my DB750 quite yet.

    My main issue is the preamp gain. Basically, I want to get all that tubey goodness without much volume (sometimes, not always). I've noticed that the tube preamp doesn't seem to really kick in unless the master volume is around 2:00-3:00ish.

    So I had this idea. Savage Audio is just a hop, skip, and a jump away from my house (OK, it's about 2 hours away). What I'm thinking is taking the amp to them and seeing if they could "mod" it a little bit. From what I've been told, they can do just about anything with any amp.

    My idea is to wire a "hot plate," of sorts, to the preamp so I can get that tube grit/warmth at pretty much any volume. Basically, splitting the gain stage into its own separate Gain/Master series - with the master cutting the output, so I can tune in/out the amount of gain.

    Would this even be doable?

    I'm not very tech-smart, so if any terms or anything are off... my bad :D.
  2. Matt Call

    Matt Call Supporting Member

    Aug 1, 2004
    Minneapolis, MN
    Anyone have an idea if this would be doable; and if it is, how much it'd cost?
  3. ArwinH

    ArwinH run rabbit run

    Dec 1, 2005
    Southern California
    Have you considered maybe using a less efficient cab?
    You would be able to hit that gian level with less volume, and you would most likely end up with a smaller, lighter cab.
  4. Well, there's really no way to wire an attenuator in the signal path of an amp. An attenuator is designed to go between the output trasnformer and the speakers when using a tube amp. It takes some of the power and turns it into heat energy as opposed to sound energy (eventually). The amp is designed to have a very specific amount of pre-amp output from the phase inverter feeding the output transistors. You can't just change that. Although that's what the master esseitially does, the amp already has a master.

    I had this problem with my 750, it's tough to get that pre-amp working without ramping the volume up real quick. I haven't yet, but i'm thinking about trying a lower gain pre-tube in one of the later gain stages in the pre-amp. The phase inverter tube is already a 12AU-7...but I may try another 12AU in the 3rd position or something like that. I need to contact Aguilar and find out which tube is which, as the effects loop is tube driven as well.

    As a side note...i've found running the EQ knobs at higher settings helps out with getting the pre-amp to saturate a bit earlier on.

  5. Eric Cioe

    Eric Cioe

    Jun 4, 2001
    Missoula, MT
    Use lower gain tubes! Put 5751s (70% gain of 12AX7s) in all of your preamp slots (leave the driver alone), and watch your tone totally change. An easy mod that sounds like it'd do what you want for cheap.
  6. Matt Call

    Matt Call Supporting Member

    Aug 1, 2004
    Minneapolis, MN
    Mmm... I'd thought of putting some different tubes.

    I was pretty sure that the "hotplate" idea wouldn't work; and figured that someone would know more than I do about it.

    Thanks everyone!
  7. FunkyLemz


    Oct 17, 2005
    Los Angeles, CA
    try the tube idea, but dont get rid of the baby. Changing cabs would do a lot too. Ive played my DB through many cabs.
  8. ArwinH

    ArwinH run rabbit run

    Dec 1, 2005
    Southern California
    Funny, right now I'm finding that the db750 isn't cutting it volume wise in practices :confused:

    I don't get why either,it's always been supah loud.
  9. jasonbraatz


    Oct 18, 2000
    Oakland, CA

    I'm pretty sure you've gone deaf.
  10. ArwinH

    ArwinH run rabbit run

    Dec 1, 2005
    Southern California
    This was my first assumption, but I used to annihalite a 100watt all tube marhsall run through a 412 with this rig, and now I'm strugglin against a 50 watt valvestate with a 412. I'm assumin the rehearsa; space is playin tricks on me, so I'll have to try a new space and hope for the best.

    Honestly though, loss of hearing is not even funny to me, this is why I wear earplugs whenerv I know I'm going to be dealin with a lot of decibels.
  11. Juct kickin around ideas here, but...

    There was a guy around here recently who had a tube head modded to be able to switch off pairs oftubes, effectively lowering the volume but still being able to crank the master volume and gain and such.

    Just a though.
  12. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Pasco, WA
    Have you considered this mod?

    Click here.


  13. That's EXACTLY the mod I was talking about. Weird.
  14. A 12AU7 is probably not the answer to your problem. While perceived (apparent volume for a given "volume knob" setting) as a "lower gain" tube, the 12AU7 actually has higher gain than a 12ax7...resulting in more clean headroom (. If you're trying for a more saturated tone - this isn't the solution as you've effectively raised your "saturation" floor even higher.

    I'm not a technical guy - so if you want to know the specifics behind this...page psychobassguy here on TB. I think he actually invented tube amplification in a former life. In any case, he can explain it.

  15. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Pasco, WA


    Crud, I knew that.


  16. kjones


    Dec 4, 2004
    I'm not sure I understand too well what's going on. I'm assuming you have the input switch set to passive? I understand you're using active basses, but I'm sure you know Aguilar recommends the passive setting unless you're just blowing out the input side.

    On many songs I play, I'm going for that early Cream Jack Bruce sort of natural overdrive, and I get it with the gain set to 12:00 - 1:00. The master is usually in the 10:30ish range, and that's playing in a band with a heavy hitting drummers, one guitar player with a Marshall half-stack, and one with a Dr. Z Maz 38.

    So I guess my first suggestion would be, set it to passive, turn your gain up and your volume down.
  17. Big String

    Big String Supporting Member

    Apr 22, 2000
    Northwest Indiana
    I concure exactly with K.
  18. eots


    Dec 18, 2004
    Morris, IL.
    Why can't you just turn down the master and turn up the gain?
    Another thought, run a cable from your send to return and use the send/return knobs up front to lower volume without affecting tone, using gain ,eq, and master to get the tone you want.

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