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Overdrive Knob

Discussion in 'Pickups & Electronics [BG]' started by anotherbassist, Sep 13, 2005.

  1. The text says the tone knob will control the OD. That does look kind of cool, but considering how picky most of us[bassists]are about OD/distortion, I wonder how well it would work on bass(isn't it intended for guitar?).
  2. the guitarist in my band has one and likes it alot. I asked stew mac a while ago about how it would work with bass and they said their shouldnt be a problem although I never got around to it. It doesnt really dist the sound but it does give it a bit of grit
  3. Trevorus


    Oct 18, 2002
    Urbana, IL
    That thing is so easy to make. It is two diodes wired in opposing directions. That give you the clipping, and getting diodes is a lot cheaper.
  4. popinfresh


    Dec 23, 2004
    Melbourne, Aus
    Hmm, i'd rather not use something like that. Unless it was a switch or similar. I don't have enough time to fiddle a knob when going between o/d and clean.

    I'd find it much easier to just use a footpedal..
  5. Trevorus


    Oct 18, 2002
    Urbana, IL
    you could wire it up with a switch... that would be rally easy.
  6. yep...you can pick up a couple of 1N4148 or 1N914 for a few cents each... that's just a little bit cheaper than the $27 that stewmac is charging...

    heck I built an entire preamp for half of that...
  7. Could you explain more about the diodes? I don't know anything about electronics, much less what diodes are. Do you just solder them together? Then how do you attach it to the bass? Also how would I wire a switch because I would rather put a switch than have it as a knob?
  8. A9X


    Dec 27, 2003
    Sinny, Oztraya
    That is providing you have enough level to drive the diodes. Might be a problem with some passive basses.
  9. Care to explain?
  10. shyanel


    Sep 14, 2005
    I too am very much interested in this, I barely use the blend control on my Yamaha RBX760A so i'd be interested to know if I could wire an overdrive circuit to that. If someone could drop me an email explaining that'd be even better as it'd mean i'd have a record of whatever gubbins i'll need and how to wire them in.

    Don't worry if there's any dodgy soldering to do, i'm perfectly comfortable with a soldering iron.
  11. okabass


    Mar 19, 2005
    I recommend to use schottky diodes on a passive bass.
  12. Matt H

    Matt H

    Jul 30, 2005
    Ithaca, NY
    the overdrive circuit they're charing 27 bucks for is about a dollar worth of parts. (more if you use a high quality pot, perhaps).

    long story short- diodes can be used to clip the signal.

    imagine you took a sine-wave (a big S looking thing) and then tried to push it through a "pipe" that was smaller than it was (from peak to peak).

    what happens? well, the pipe can only carry so much of the signal, the parts that dont' fit? well, they get clipped off... hence "clipping"...

    the way the diodes here work are to clip the signal assymetrically (due to the two diodes being wired in reverse of each other).

    there's more to this at work, but that's a good enough start.

    as for putting this on a switch- it'd be simple. you could wire the diodes side by side (reversed from each other). then, take a DPDT switch, and wire it so that your signal passes through either diodes, or the "other" side of the switch, where you've wired in a little jumper connection.

    that'll completely remove the diodes from your path.

    btw- this is generally regarded to sound like crap.

    HOWEVER- when jack bruce started to have issues being able to crank the marshalls to "get his sound" on that SG bass (the eb3? i guess... right?), his tech wired in a diode in series with his bridge pickup, to add a little bit of fuzz/grit... to get that distorted sound at lower volume.
  13. shyanel


    Sep 14, 2005
    Is there any chance you could let me know exactly what the parts are called that i'd need to do it and maybe if I can be very cheeky could you email me a bit of a schematic or something.

    I REALLY wanna give this a shot, it's not as if I couldn't undo it once it's in and as i want to put it on my blend knob i'd be losing a knob I barely use.

    My Yamaha has 1V 1Bass +/- 1Treble +/- and 1 Blend I am right in thinking it'd be the blend i'd put it on, right?
  14. Where exactly do the diodes go?
  15. Matt H

    Matt H

    Jul 30, 2005
    Ithaca, NY
    the diodes go in series with the "hot" connection...

    where in the path you put them? that's up to you.
  16. Sorry but I have no clue what you mean by "series" and the "hot connection."
    Here's a picture of a control cavity of a bass, can you show me all this stuff that you are talking about?http://www.bassplayer.com/Pictures/web/q/c/v/washburnGJ7P1135.jpg
  17. Matt H

    Matt H

    Jul 30, 2005
    Ithaca, NY
    show you? no... but honestly, you should know the difference between hot and ground wires before you start messing with stuff.
  18. superfly


    Aug 4, 2004
    Diode tease. :D
  19. A9X


    Dec 27, 2003
    Sinny, Oztraya
    No. They go in the shunt path, ie from hot to ground. Putting them in series with the pickup will mean that they stop all signal until the threshold of the diode's forward conduction is passed. For a 1N914 that'll be somewhere above 275mV (see Fairchild 1N914 datasheet, p2 Vf vs If curve). Sonically, the effect will be somewhat like a noise gate with the threshold set very high, or to make use of your pipe analogy, only the bits of the signal that are above the pipe will be passed, ie the peaks.

    Putting them in shunt means that when the threshold voltage is exceed, the diodes will forward conduct and the signal that exceeds the threshold will be 'cut off'. The is somewhat similar to clipping in a solidstate amp where the signal has reached the voltage rails, ie can't go any higher.

    Note that in the StewMac page it states that the "Black Ice circuitry replaces the capacitor on a guitar's tone control" so it's in the shunt path where it should be.

    My earlier comment "That is providing you have enough level to drive the diodes. Might be a problem with some passive basses" was based upon the diodes being in the shunt path at the end of a large value series resistor (tone control pot), means that with some basses with pickups that generate a lowish signal eg many Barts, there may not be enough level from the pickups to drive the diodes on and create the desired distortion effect, or that the effect may be minimal or of limited range of usefulness. For $US27 that's a bit of a risk, but for the 10c two 1N914 / 1N4148 diodes and a few minutes, it could be a worthwhile experiment.

    How to> Buy two diodes - try your local Radio Shack or the like. On the cylindrical casing there is a white stripe on one end; see attachment below. Place the diodes so that the stripes are facing away from each other. Twist leads together at both ends to make a single 'composite' diode assembly and solder together. Unsolder tone control capacitor. Solder diodes in it's place; won't matter which way around you solder them in.

    Diode circuit symbol and drawing of the typical casing.