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[PROJECT] Simple Dub Box and Bass Booster

Discussion in 'Pickups & Electronics [BG]' started by Dark Horse, Nov 17, 2009.

  1. Dark Horse

    Dark Horse Supporting Member

    Jul 31, 2008
    Austin, TX
    Endorsing Artist: Eastwood Guitars, CHC Guitars, GHS strings
    This one is slightly more advanced, but still easy to build for those with a little soldering experience. I didn't do an "EZ-Build" diagram - maybe I'll add that later.

    Anyway, this is a simple Jfet based "booster" circuit. Instead of just making it a "clean boost", I expanded its use by adding the "Simple Varitone" circuit. You can find the Simple Varitone posted here on the site. What happens is that your signal goes into the Jfet (MPF102) and is amplified - then it goes out and variable frequencies are bled to ground (removed), unless you have the switch in the "open" position. In the "open" position, this circuit will act like a full range clean boost for your bass ! In the other positions, it can go from "just a bit of hi-cut" to "full on dub-reggae" bassy goodness !

    A few things to keep in mind - you may need to adjust the value of the 10k resistor slightly to get the best sound. Certainly you could use a trim pot instead of the resistor, but I wanted to keep the project as simple as possible, without sacrificing tone and versatility. Use a 100k LOG pot for the volume pot. Lug 1 will connect to ground, lug 2 goes to output, and lug 3 from the circuit - hooked up just like a regular volume control.

    I used a Jfet because it tends to, at least to my ears, sound better than a transistor based boost - at least on bass. You can use other Jfets besides the MPF102, like a J201 or 2N5457 ... but the MPF102 is easily available at Radio Shack as is the switch !), so in an effort to "keep it simple", I used the MPF102.

    There are very few parts in this circuit, so it is ideal for a builder with minimal experience. You should, however, be familiar with the use of a soldering iron, how to hook up a battery to a circuit, etc before trying this project. There are a lot of great places to get info like this on the web, including www.diystompboxes.com and many others.

    Enjoy !

  2. CrackBass


    Aug 10, 2004
    Have you determined the power draw of this circit? I ask because it occured to me that this might be a viable onboard active option for a pbass, for those that don't want to route out a battery compartment. If it would run off a small power supply (watch battery etc..) lower voltage or amperage with decent battery life.

    Don't go out of your way, just wondering if you had considered the possibilities. I'm guessing you have, if so share your thoughts on the matter.

    I'm currently considering the passive varitone you posted for my pbass.
  3. Dark Horse

    Dark Horse Supporting Member

    Jul 31, 2008
    Austin, TX
    Endorsing Artist: Eastwood Guitars, CHC Guitars, GHS strings
    I haven't figured it out, but it should be fairly low. I would think that as long as you use a TRS jack for your bass' output jack (to disconnect power when not plugged in), you should get a nice long life out of it.

    This could certainly be altered to run on something like a 3V watch battery. Obviously you'd want to adjust the 10k resistor, and probably lower the 1k resistor (to maybe 330 - 390 ohms), but it should work ok. Still, I'd recommend breadboarding it first, even if you just breadboard the "boost" section.

    BTW - the passive varitone - though not really a "true" varitone - works GREAT. I posted some alternate values in that thread that will work if you are going primarily for fatter, bassier tones.