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Bartolini NTBT-918 - Extra parts ???

Discussion in 'Pickups & Electronics [BG]' started by MoireBass, Oct 23, 2010.

  1. I just got a Bartolini NTBTG-918 preamp new (eBay) and it came with a small brown paper envelope in the box that contained a piece of cardboard with five resistors and four capacitors taped to it. Nowhere on the included schematic or anywhere I could find on Bartolini's website was there any information on what these parts might be used for.

    They are (in order):
    1) 2Kohm
    1) 6.8 Kohm
    1) 10Kohm
    1) 27 Kohm
    2) .022 uF
    2) .047 uF
    1) 2.7 Kohm

    There *was* a web schematic for Bartolini's 1970s TBT preamp that showed adding capacitors across the legs of the tone controls to change the affected frequency somewhat. No info on if this is in any way relevant to the NTBTG-918 or a reason for doing that. Since these preamps are sold for use for bass or guitar, doesn't it make sense that you might add a couple of caps to set the frequency bands to be optimal for one instrument or the other?

    Bartolini is famously difficult to get an answer out of though, supposedly even worse than Ken Smith is. They don't have an email address or phone number posted on their website, just a FAX number. I'll send them a FAX on this, but since these are such widely used preamps, maybe someone here on TB knows what the extra parts are for? Thanks!
  2. badbassjd


    Oct 27, 2010
  3. Thanks. Yeah, I saw that (very old) document. The problem is I don't think we can safely assume that the information will be accurate for the NTBT preamp. Maybe, maybe not.

    The TBT preamp required external capacitors to set the frequency corners, while the NTBT pulled those caps within the preamp module so that the default installation required no additional parts. For the bass control, it's no problem, additional capacitance across the legs of the pot sum with the capacitance within the preamp module and lower the bass band corner frequency as expected (per the text). The problem is with treble control, additional capacitance in series with the control doesn't sum directly with the capacitors inside the module, instead the total capacitance is the reciprocal of the sum of the reciprocals of the two capacitors (like two resistors in parallel). So if you add an external capacitor in series with the internal capacitor that is equal to it in value, the total capacitance is half what either one would be. In fact, no matter how big a capacitor you put in series with the internal capacitor, the result can never be larger than the internal capacitance alone. This means that adding an external series capacitor can only *raise* the corner frequency of the treble control, can never lower it. And several TB posters have commented that they think the NTBT treble control is active at too high of a frequency anyway.

    This is a very commonly-used preamp, so figured that information on optimizing its use for bass would be part of the info base on TB, but searched and didn't find anything.
  4. Rano Bass

    Rano Bass

    Sep 9, 2006
    Tijuana Mex.
    I dont think it is too high, to my ears the treble frequency boosts midrange too.

    When i bought my NTBT preamp it also had those extra caps and resistences too but all the pics of basses i saw with that preamp never used anything extra so i didn't used those either.
  5. A back-in-town-and-this-thread-needs-some-attention bump....
  6. wmheilma


    Jan 5, 2010

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