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Piezo strip uneven string volume [ABG]

Discussion in 'Pickups & Electronics [BG]' started by Tgolsson, Feb 11, 2014.

  1. Tgolsson

    Tgolsson

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    Hello!

    I was making some recordings with a friend the other day, and since we were making demos for our troubadour duo I decided to use my acoustic bass, a Fender T-bucket. It had quite old and boring strings, so I decided to put on some flats, TI jazz, to give it a more upright sound. Being unplugged it sounds truly awesome, but when I plug it in I get about 9db difference from E to G. It has always been unbalanced, but perhaps by 3db.

    The ABG has an under saddle piezo strip, and I made sure to seat it properly after changing strings (wide side of saddle below E and strip centered in the trench). The EQ is flat on the preamp. I have these issues no matter if I go direct into my card, or if I go with a preamp and line input, or if I use my digital preamp with SPDIF. There is a very notable volume difference between strings when plugged into an amp.

    Any ideas what I could do to solve this?
  2. MPU

    MPU

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    Maybe your saddle is a bit too tight on lower output side? It should be loose enough to transfer the vibration of the strings to the piezo strip.
  3. Tgolsson

    Tgolsson

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    How would I go about lowering the pressure of the saddle? :)
  4. oerk

    oerk

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    This doesn't address your piezo issue, but how do you feel about micing your bass, if you're recording anyway? This will give you a more natural sound than a piezo ever could.
  5. Tgolsson

    Tgolsson

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    I'm actually intending to do that in the future, but right now I'm at a lack of microphones suitable for basses. I'm currently recording for a project with a friend where we're trying to do it all live, and are already using 6 channels.

    I also don't think I would want to go fully mic'd because it has quite low volume compared to the rest of the instruments, so I would probably end up using it as a complement to the line signal... Putting us at 7 channels for a duo. :p
  6. MPU

    MPU

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    Make sure the saddle is not too tight on the saddle slot. Also make sure you have straight saddle and straight saddle slot. You want even pressure on all strings. Sand the saddle if needed.
  7. smperry

    smperry Moderator Supporting Member

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    +1 to sanding the edge of the saddle a bit to make sure it's fully seated.
  8. Tgolsson

    Tgolsson

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    The saddle is radiused by standard, would estimate by about 1-2mm, with a bias towards one end. This wider end is towards the E side right now, and I'm 99 % certain that it has always been in that direction. Would rather not sand it down, but will try reseating it.
  9. smperry

    smperry Moderator Supporting Member

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    I think I'm not being clear. I don't mean to suggest you sand the top down in terms of the radius, I'm talking about the side (front or back) so that it fits in the slot well and goes in all the way. If the saddle isn't in all the way, you get an uneven response. I had a similar issue with a former bass.
  10. lz4005

    lz4005

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    You said you re-seated the bridge saddle...does that mean you removed all of the strings at once and pulled the bridge saddle out? Don't do that.

    On anything with bridge parts that are held on with string pressure you can have things shift when you remove all that pressure and cause problems. Change one string at a time so that all the bridge parts stay in the same place.

    I'd look at the tension on the strings too. If there is a major difference in the tension of some of the individual strings it could result in a volume difference as compared to the old ones.
  11. Tgolsson

    Tgolsson

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    Lz4005: I usually do not do that, but the peg on the E-string was stuck, so I had to remove all strings in order to get some space to loosen it. When I went to put the strings back on I accidentially knocked the saddle out. After making sure that the piezo still looked correct I put the saddle back on and restringed it, making sure to maintain roughly even tension until I was fully tuned (to prevent the saddle from 'twisting' from the uneven pressure.

    I've also come to the conclusion that the strings might be an issue, as the E-string in the TI-flats is noticeably thicker than the rest... The much increased mass probably means that when I pluck it, it exerts a lot more energy on the saddle, causing much higher output.

    Smperry: The saddle is about 1mm shorter than the trench, so I don't think that's an issue. :)
  12. lz4005

    lz4005

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    Or it could be tighter and pushing down harder. Related to mass, certainly.

    Piezos can be sensitive to having balanced tension on the strings. It could just be that those strings don't agree with that bass and there's not much you can do about it.
  13. peterkidd

    peterkidd Supporting Member

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    I've had a couple of eab's that I could not balance the string volumes.

    I ended up cutting the saddle into separate sections for each string.

    In those cases, at least, it worked well.
  14. lz4005

    lz4005

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    I've heard of people doing that, but never done it myself. As I understand it, it would mainly compensate for having the bottom of the saddle or the bottom of the slot not perfectly flat.

    In theory if the problem is unbalanced string tension it could make the problem worse. I think.
  15. Tgolsson

    Tgolsson

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    Could the thickness of the string, and the lower break angle it causes over the saddle, means that the E-string exerts mostly forward pressure on the saddle instead of keeping it sealed against the piezo?
  16. RobbieK

    RobbieK

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    I do just this job all the time. Often the saddle is actually too loose, and under string tension it tilts forward ever so slightly. If this is the case you either need a new saddle, or you need a strip of superglue along the lower back, dried then filed as a filler/shim. The saddle should slide in snuggly, but with no resistance.

    The bottom of an acoustic saddle really has to be dead level and square. You need to hold it against a straight edge and up to the light and not see even a tiny sliver of light. Of course the bottom of the slot also needs to be dead flat, but these days with cnc machining in most factories, they are generally pretty good. I would certainly check for any tiny wood fibres of other stuff that may be under the piezo. If you need to level the bottom of the saddle (they are often very uneven from low and mid priced guitars), you need to use a good file that you have also checked against a straight edge. You can also stick some sandpaper to a piece of glass or something. If you need to work the slot, then a 3mm chisel will tidy a few rough edges, or it's a job for a dremel with a router base.

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