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How Do I Know if I Need a Preamp?

Discussion in 'Amps, Mics & Pickups [DB]' started by Beginner Bass, Sep 30, 2010.

  1. Beginner Bass

    Beginner Bass

    Jul 8, 2009
    Round Rock, TX
    A&R, Soulless Corporation Records
    I'm working on building a piezo pickup to sit under the bridge, and as I get closer to completion (Hopefully Monday), I'm getting closer to facing the trouble of whether or not I will need something else in the signal chain for it to sound good.

    I was given a sort of informal commission to build a piezo pickup for the DB used in jazz band. I'm hoping to have it ready to play by Monday, so I need to know very soon if I will need some sort of buffer or preamp for my bass. It will be going through a Crate keyboard amp through an input with a +10db boost (The other 2 channels are being used.) I found a cheap buffer design that I could pick up at Radio Shack for about $10, but I need to know if I'll need it.

    Can anyone give any advice on this, or is it just one of those things I won't know until I try it? Haste in replies would be greatly appreciated.
  2. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    Cape of New Jersey
    Big Cheese Emeritus: Gollihur Music (retired)
  3. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    The discussion on Bob's site is quite useful and, for the most part, correct. Piezo transducers are not in the 1-2 Mohm range. Rather, they like to look into an input or "load" that is in the 1-2 Mohm range. As has been discussed here several times, the effective "filter" created by loading a piezo in that manner preserves the desirable low-frequency response.

    So, if you plan to plug your piezo transducer into an amp having an input impedance of >1 Mohm then, insofar as frequency response goes, you should be fine. Depending on the circuit characteristics of the amp you use, you may find that infrasonics generated by the piezo are passed right through to the power amp and driver, wasting precious power and dynamic range.

    All this is solved in one neat package: fdeck's pre/HPF that combines a rather ideal piezo buffer amp with an adjustable high-pass filter.

    You may know that the "secret" to the success of a good piezo bridge-wing pickup is largely in the mass-loading of the case in which it is sandwiched. That has a substantial effect on the overall response and successful makers of piezo bridge-wing pickups tend to guard very closely the details concerning the nature of the materials used.

    In another example of Bob Gollihur being a class act who cares about what's on his site, he already edited his discussion of piezo's and input impedance and PM'ed me. Again, I think the plain-English discussions on his site are enormously helpful and enlightening to many players.
  4. Ric Vice

    Ric Vice Supporting Member

    Jul 2, 2005
    Olivette, Missouri
    FDecks HPF Buffer Preamp is ideal for this you can buy a unit from him or here is the link to how to build one.

    http://personalpages.tds.net/~fdeck/bass/ on the page is a link to the "Quick and Dirty Piezo Preamp"

    http://fittell.id.au/piezo/ How to build a Piezo for Bass
  5. Beginner Bass

    Beginner Bass

    Jul 8, 2009
    Round Rock, TX
    A&R, Soulless Corporation Records
    Thanks. I actually read your article there before. But I couldn't find much information on the matter, other than that, so I thought I would try and get a larger sample size, so to speak.

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