On-board preamp - DIY circuit?

Discussion in 'Electric Upright Basses (EUB's) [DB]' started by ToneRanger, May 30, 2005.

  1. Hi all,

    I need a preamp to buffer a pair of pickups in my EUB - magnetic & piezo. I don't need eq or gain, so I'm pretty sure a simple circuit with a handful of components will do it. This looks like it would do what I need:


    I'd probably just use the front end and ignore the tone controls. I know enough about electronics to construct a simple circuit like this, but not enough to know in advance whether it's suitable - anyone else tried this, or have an effective alternative?

    (I know there are suitable preamps on the market, but they're mostly in the USA, I'm in Oz, and they seem to triple in price by the time they get here. Gives extra motivation to DIY.)
  2. mje


    Aug 1, 2002
    Southeast Michigan
    The input impedance is a bit low for piezo pickups. You might try chnaging the 250K pot on the piezo side for a 5 meg pot, but that might be a bit noisy. Another option is to put a fixed 5 meg or 10 meg resistor there, and do gain control later- like make that 2K2 resistor a 2.5K pot instead.

    I know we have an engineer in here who might venture an opinion.
  3. HvC


    Jun 27, 2004
  4. robgrow

    robgrow Supporting Member

    May 1, 2004
    Cincinnati, Ohio
    If all you need is buffering, then you might want to consider a simple FET source-follower circuit such as the one I posted in this thread: http://www.talkbass.com/forum/showthread.php?p=2030173#post2030173

    It has a very high impedance input, relatively low output impedance, has approx. unity gain, and the output is in phase with the input.

    If you need some gain, then you might want to consider the simple circuit on Don Tillman's web site: http://www.till.com/articles/GuitarPreamp/

    One thing to note is that the output is 180 degrees out of phase with the input with this circuit. If you need a non-inverting gain stage, you could use use 2 of the Tillman circuits in series -- possibly with a volume pot between them (in place of R1 on the second stage).

  5. Please follow up with your success/progress/choice as I am quickly reaching that stage of my EUB as well and am not quite shure which preamp circuit to build...
  6. Thanks folks, that's exactly what I needed to know!
    I'll buy a handful of components and see if I can make it work.
  7. nsagan01


    Nov 10, 2007
    Does anyone have any suggestions as to how I would go about wiring up the DTar Volume and tone module to a piezofilm p/u and kemo m040 preamp?