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Finding and wiring a gain trim pot for an old Bartolini NTBT

Discussion in 'Pickups & Electronics [BG]' started by Justyn, Apr 8, 2004.


  1. Justyn

    Justyn Supporting Member

    Jun 24, 2002
    Richmond, VA
    Hi all.

    So I've got this old Bartolini NTBT preamp that was in an MTD Kingston 5 I owned briefly. It was installed without a gain trim pot, so the signal was wicked hot coming out of the bass. I replaced it with a new NMBT and later sold the bass, which leaves me with a perfectly good, albeit somewhat old, NTBT preamp. As it so happens, I've just bought a bass that has a nice Bart M4 pickup wired to a passive volume and tone and I'd like to put this preamp to use but am decidedly limited by my own lack of knowledge. I can solder with the best of them (or at least the pretty-good of them), but I'm not sure where one might acquire a gain trim pot or how to properly wire it in.

    On the plus side, there's a helpful diagram on the Bart site that shows a trim pot attached to three wires, a white one, a blue one, and a grey one, and between the white one and the gain pot there's a little bit labeled 1.3K-ohm which I'm assuming is a resistor.

    Armed with this knowledge I was thinking of heading over to Radio Shack and surveying the possibilities, but one thing is kind of worrying me...how do I know which wire goes to which prong coming off the gain pot?

    Can anyone suggest a better resource for parts and/or give me some help in wiring this up properly?

    Thanks very much,
    J.
     
  2. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Have jacked with lots of Bart preamps, in fact, all of them to my knowledge. First thing I'd do is wire it without the gain. Just because it was hot with the old pups doesn't mean it will be with these. If you've got a volume and gain on your amp, you can just use the amp gain if you need it, at least for the time being.

    The other things is that I've done pretty much everything wrong you can do in wiring and haven't trashed anything yet. Although I've heard about the potential for a meltdown, onboard electronics are pretty indestructible (but you have to watch you amp). If anybody could have screwed something up, it'd have been me. If I got to that point, I'd just take an educated stab at your wires till you get it right. It's worked for me when all else has failed.

    For what it's worth.
     
  3. the white and blue wires go on the outer terminals and the grey goes on the middle
    since a trim pot is just like a regular pot it doesnt matter if the white or blue go on the left or right it will only change the direction you have to turn the trim pot in order to increase (or decrease) gain

    i have one of the new ntbt-918 preamps, mine doesnt have a resistor on the white wire, but i did see that in the diagram you mentioned. *shrugs*
     
  4. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    From what I understand with nothing connected to those wires (and not wired together) there is no boost.

    I have the instructions from a TBIBT and it just has a gray and white wire and says connecting a 6.8k-ohm resistor between the 2 wires gives 6db flat boost, a 3.6 k-ohm resistor and an unpolarized 1mfd capacitor in series gives a 12db boost in the mids and treble.
     
  5. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    I have the instructions from a TBIBT and it just has a gray and white wire and says connecting a 6.8k-ohm resistor between the 2 wires gives 6db flat boost, a 3.6 k-ohm resistor and an unpolarized 1mfd capacitor in series gives a 12db boost in the mids and treble.

    Seems I've got something laying around that says something to that effect too. I'll have a look.
     
  6. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Okay,

    located this piece of script I've got. From what I can gather, if you got any NTBT, new or not, it should have the same wiring scheme. Is your's the same as the Bart site one? That one of Moo's is apparently the predicessor to the NTBT as this piece mentions the TBT & XTBT as previous units.

    From what I can gather from what this says, the frequency range of the bass and treble controls is preset with built-in capacitors and it says nothing at this point about a trim pot being part of that. The bass automatically boosts and cuts up to 16 db depending on where you set the bass pot with 5 being flat. The treble atuomatically boosts to 18 db and cuts to 16 db, again flat at the detent. This is using 50 k linear pots. It says nothing about what to do with the wires allocated for a trim pot but I gather they can just be capped off. It does say to definetly not let them ground out in any manner. So apprently those wires are only there in the event of use of a trim pot.

    Also, I've had Bart 3 bands that had a trim pot and some that didn't that were the same units, and still may have, I'd have to look. So I think you may be good to go as it is. Find out.

    Most of what's talked about in this piece is how to utilize additional capacitors to alter the frequency range of either the bass or treble controls "if necessary," as it says - implying it shouldn't be necessary. But they sure spent a lot of time talking about something that shouldn't be necessary.

    For what it's worth.
     
  7. Justyn

    Justyn Supporting Member

    Jun 24, 2002
    Richmond, VA
    Thanks for all the help friends! Step one will be to try my old Bart (and yes, it's the one they have a diagram for on the Bart site, the '9v NTBT i' with no gain pot and the wires capped off. Based on how that goes I'll add bits until I've got things how I want them.

    Thanks agin for all your help. I need to read all the replies over again and make sure I understand them all but I think I'll get it though I might have a few follow-up questions.

    J.
     
  8. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Well I've got plenty of info on using capacitors to alter it but it's a little on the confusing side to me. At any rate, from what that piece I have says, your pots act as you gain controls. I guess maybe a trim pot just gives you more control.