Discussion in 'Pickups & Electronics [BG]' started by Diegombass, Mar 26, 2021.

  1. Diegombass


    Sep 19, 2012
    Hi, I have an electro-acoustic bass with a Bartolini humbucker and an undersaddle piezo.

    I have tried a lot of configurations. For the moment it works for me Bartolini passive with volume and tone, and piezo buffered with the Mint Box Buffer (http://www.scotthelmke.com/Mint-box-buffer.html) with volume and tone. Each pickup mixed in my Hx Effects, each with its own passive tone frequencies.

    There are some changes that I want to achieve: varitone in both pickups and mix both pickups inside the bass. The mixer is what I don't know how to make it.

    Right now I have connected one pickup to the other through a 100k resistor. It works but I hear a volume drop, and I would like to rise the piezo volume a bit more.

    My knowledge in electronics is poor. May you tell me the way to increase the gain on the Mint Box Buffer? Do I need some more buffers to mix up these pickups instead of doing it in passive mode? Do I need to use different numbers in these mixer resistors?

    Thank you very much!
  2. There is no way to increase the gain of that fet circuit. It will have a slightly smaller output voltage than its input. It is designed for current gain, not voltage.

    I'd recommend buffering the magnetic pickup as well, but use say a 100k resistor instead of the 10M resistor, so it sounds fairly normal. The input coupling cap will also have to be increased to say, 1uF to avoid bass roll-off.

    A varitone won't really work on a piezo pickup. You can't hurt anything by trying it, but it won't do what you think.

    As for mixing the two signals, you could use a couple of pots and summing resistors as a (passive) mixer. Then you might need a gain recovery stage on the end of it.
  3. Diegombass


    Sep 19, 2012
    Thanks for your reply :)
    Now I have the best setup I have achieve. Piezo --> Mintbox buffer (without 10k output resistor) --> 500kVolume/500kTone (I didn't have two 25K pots), with a switch for two different caps --> 10k mix resistor --> output.

    MAG --> 250k volume/ 250k tone --> 10k mix resistor --> output.

    Not quite bad volume and balance between pickups, but I would like better levels.
    I have tried a guitar amp at output, with cap on Drain resistor, but the volume is still too low. Google Image Result for https://electronicscheme.net/wp-content/uploads/2011/02/guitar-preamp-design.jpg

    I am sure I am doing wrong a lot of things, May you tell me any?:oops:

    Thank you
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