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Blending piezo and magnetic pickups - what buffer?

Discussion in 'Pickups & Electronics [BG]' started by vin97, Jun 14, 2020.

  1. Jun 14, 2020 #1
    vin97

    vin97 Inactive

    Mar 7, 2016
    Germany
    I am planning on putting some piezo saddles in my fretless bass.
    All blending should be done onboard, meaning a regular mono output.

    Obviously this will require an active buffer for the piezos but I'd like to keep the magnetic pickups fully passive if possible.

    What kind of buffer should I get (or build) to match the piezo impedance to the magnetics in order to allow for passive (master) blending?
    The whole circuit should be as simple as possible. I don't need automatic stereo switching, EQ or anything like that. The power source should be 9V DC.
     
    Last edited: Jun 14, 2020
  2. Jun 14, 2020 #2
    RobbieK

    RobbieK

    Jun 14, 2003
    Smellbourne, Oz...
    The DIY active blend control I featured on my YT channel would work for this. It is about as simple a circuit can be for this job. Use a low-noise opamp with fet inputs, and set the input resistor to 4.7M (or thereabouts) on the piezo side. Also use a short instead of the input coupling cap. For the other side if you are running the mag pickup directly in, then use a fairly low input z (100k-220k) and think about adding a load cap to simulate cable capacitance (~470p).

    When I've used twin buffer type circuits for piezo installations in the past, I've also set up a temporary phase reverse switch on the mag pickups. That way you can test and find the fullest sound with both on.

    If the mag pickup is much louder than the piezo, I'd recommend against using feedback resistance on the piezo side for gain. With such a high input z, this will noisy. Attenuate the mag side, or use a separate boost on the piezo.



     
    dwizum, RumbleBot, vin97 and 1 other person like this.
  3. Jun 14, 2020 #3
    vin97

    vin97 Inactive

    Mar 7, 2016
    Germany
    I'd like to avoid an active blend / twin buffer circuit if possible. I just want to match the piezo's level/impedance to the magnetics so that I can use a regular M/N blend pot to balance the two. A loss of power should not influence the signal of the magnetics.
     
    Last edited: Jun 14, 2020
  4. Jun 20, 2020 #4
    vin97

    vin97 Inactive

    Mar 7, 2016
    Germany
    Nothing?

    Couldn't I adjust the output impedance of a generic piezo preamp with a series resistor to match the magnetics?