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piezo bridge string balance trim pots

Discussion in 'Pickups & Electronics [BG]' started by eli, Aug 28, 2017.


  1. eli

    eli Mad showoff 7-stringer and Wish lover Supporting Member

    Dec 12, 1999
    NW suburban Chicago
    I want to add a Hipshot bridge with GraphTec saddles Hipshot 5 String A Style Piezo Bass Bridge - Best Bass Gear to a Carvin AC50 to solve a nasty string balance issue.

    What I can't find using Google is a board with the (5) pots. Anyone know (a) what these are generally called so I can search better, and/or (b) where I can get one? Do they usually come as a complete buffer, or is this a separate piece of equipment?
     
  2. lz4005

    lz4005

    Oct 22, 2013
    Have you verified there's enough solid wood in that bass to covert it from a glued on acoustic bridge to a bolt on metal one?

    Your best bet is to look for a complete preamp setup.
     
  3. eli

    eli Mad showoff 7-stringer and Wish lover Supporting Member

    Dec 12, 1999
    NW suburban Chicago
    It's actually a chambered solidbody, and under the bridge is indeed solid wood.

    I've been searching every way I can imagine, and still only coming up with single-channel preamps. Starting to wonder if these are only made by bass manufacturers for their own instruments...?
     
  4. Slidlow

    Slidlow

    Apr 15, 2009
    Oshawa, Canada
    Look up richter electronics in Germany. He makes a piezo buffer with individual volume for each string. Available from 4 to 6 string and up to 11 string on special Order. I have one for my new 6 string (see luthier section).
     
  5. eli

    eli Mad showoff 7-stringer and Wish lover Supporting Member

    Dec 12, 1999
    NW suburban Chicago
    Thanks, I finally came across him in further searching since my post. Also found a different repair guy who got the balance pretty doggone good with the single channel, so the situation is not as urgent.
     
  6. RobbieK

    RobbieK

    Jun 14, 2003
    Nice one. Was going to be my suggestion. A lot of bass techs have little experience with acoustic guitar saddles and under-saddle piezos.

    Yeah, I'd persevere tweaking the saddle. ABGs and similar under-saddle piezo bass bridges are notorious for this problem. Could've been something simple like a tiny splinter of wood in the slot or something. Or possibly the saddle was too tight in the slot and binding slightly.

    Something that works well also is slotting the saddle, a bit like a nut.

    From there you can carefully adjust the bottom surface of the saddle to improve it further.

    As for a piezo mixer, well I've designed a few of these, but only as one-offs on protoboard. There is so little call for anything like this, I've never even bothered to design a circuit board. But FWIW, it's a very simple circuit if you know someone in your area who is into audio electronics...
     
  7. The only way to get this working properly is to provide a very high impedance buffer for each string channel. If you are (or know of) an electronics man, I’d recommend chips from Analog Devices. You can get super low noise, supper low current drain chips. Place a low pass filter on each input - between the piezo and each buffer input to keep RF rubbish out - then drop a high impedance resistor to the 0volt rail; say 100 Meg ohm. This biases the buffer and gives the input resistance that the piezo will ‘see’. That part of the circuit should be very well shielded.

    On each buffer output fit a potentiometer - say, 4k7 or 10k. Feed the wipers into 5 inputs on a 5 way summing amp amp that’s the job done. Input and coupling capacitors may not be required: yes, there’ll be some DC on the pots and they’ll ‘scratch’ when turned but should be fine after that.

    I’ll use this basic scheme when I do the same job. Fortunately, as a very experienced electronics man, this will be a breeze. However I understand not everyone has that knowledge so I suggest finding a good hobbyist or professional to help. The parts may cost $20 or $30.
     

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