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Changing Preamp EQ Frequencies

Discussion in 'Pickups & Electronics [BG]' started by Technotitclan, Dec 13, 2013.

  1. Technotitclan

    Technotitclan Lurking TB from work Supporting Member

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    In one of my basses I have a Bartolini NTMB preamp. I like it a lot apart from one thing, the frequency of the bass knob. According to Bartolini the bass is centered at 30 Hz which I'm finding a little lower than I need. If I played a 5 string I may like it but I play a 4 in drop D so I don't have a need for it being that low. I was hoping that someone could assist me with calculations on a thought I had. The supplied diagrams from Bartolini give a chart of capacitors you can add to the mid to change which frequency it modifies. Looking at this chart it looks as though adding any capacitors increases the frequency it operates at starting at 250 (no capacitor) to about 1030. I'm wondering if it would be possible to add a cap to the bass side of the eq to bring it from 30Hz to 40 or 50. Its a small change but I feel it would be far more useful to me.

    Thanks in advance.
  2. LightGroove

    LightGroove

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    Depending on the resonant frequency of the room you are playing 10hz can be a lot.

    This is an interesting question..look forward to seeing the answers. BUMP!
  3. ddnidd1

    ddnidd1

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    The bass corner frequency is set internally. AFAIK there is no way to adjust that. The circuits for setting a mid peak frequency and a bass shelf corner frequency are different.
  4. Technotitclan

    Technotitclan Lurking TB from work Supporting Member

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    The frequency is also set internally for the mid but Bart provides info on how to change it by adding capacitors to one of the connections on the mid pot. I figured if it can be done with the mid maybe it can be done with the bass.

    I'm more than happy experimenting with it but I'd like someones recommendation on what cap value to start with to add about 10hz.

    For reference, here is Bartolini's installation instructions. This is how I have mine set up with the exception of a volume push/pull for a passive bypass. http://www.bartolini.net/instructions/electronics/ntmb/Ntmb_918.pdf
  5. ddnidd1

    ddnidd1

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    They are different electronic circuits so just adding a cap won't work. I'm familiar with the NTMB. I have a few.
  6. ddnidd1

    ddnidd1

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  7. Passinwind

    Passinwind Charlie Escher Supporting Member

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    I can put the whole schematic in a Spice model and give you a definitive answer, but it may take me a few days to get around to it. Just eyeballing it, you could try adding a cap in the 1uF-10uF range between the green lead and the 25K volume pot. This will roll off the low-lows and move the effective bass center/corner frequency up a bit. The smaller the cap value, the more rolloff. It'll also have some effect on available boost and cut and overall frequency response (less boost, more cut, less low bass at "flat" detent), which you may or may not like.;)

    Using something like fdeck's high pass filter would give you variable control, and a steeper rolloff if desired.
  8. Technotitclan

    Technotitclan Lurking TB from work Supporting Member

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    It its not too much hassle running it in a model would be appreciated but you have mostly given me the answer I'm looking for. I have different caps available and really just needed a starting point and an idea of how it will effect if if i go up or down.

    Having less available boost and more cut is not really a concern since I don't ever use full boost anyway and if less bass at flat because an issue i can always just turn it up a tad or switch to passive. I use the preamp maybe about 40% of the time so its not a huge issue if its altered a bit by this mod.

    I have considered fdeck before but that was a while ago before switching to the bart. I may look at it again.
  9. Passinwind

    Passinwind Charlie Escher Supporting Member

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    Cool, and please keep us posted on your findings. I have an NTMB in one bass and eventually plan to do my own onboard preamp design, so doing a model will be useful to me anyway. I can just hack one of my existing models to get ballpark results, so the hassle factor is pretty low actually.
  10. Technotitclan

    Technotitclan Lurking TB from work Supporting Member

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    Ddnidd1, That thread has a lot of good info. Thank you for that. My original search did not turn up that thread which tells me I need to work on my searching skills again.

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