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Active pre- ON/OFF switching

Discussion in 'Pickups & Electronics [BG]' started by coyoteboy, Dec 16, 2003.


  1. coyoteboy

    coyoteboy easy there, Ned Supporting Member

    Mar 29, 2000
    Sactomato, CA
    I beleive I have seen active basses with an on/off switch for the preamp, and I'm curious about how difficult it may be to add this feature to an existing active pre-?

    Could one simply replace the volume knob with a pull switch and wire that switch either inline with the battery leads, or to the ouput? Might this also be used to save battery life w/o unplugging the cord every time??

    Thanks folks!
     
  2. When I was having my bass made I thought the same thing. That if I put it on passive that it wouldn't drain the battery. But that's not the case. The battery gets triggered as soon as you plug in the jack. Unless there is a way to bypass that somehow that I don't know of. I had an On/Off switch installed and I like it a lot.

    I'm sure if you had someone who knows what they're doing they could do the volume knob deal. That's what I have on mine, push/pull volume knob that turns the preamp on and off.
     
  3. coyoteboy

    coyoteboy easy there, Ned Supporting Member

    Mar 29, 2000
    Sactomato, CA
    Cool Beans! thanks.

    anyone else?
     
  4. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    as chump stain said, the bypass won't really stop battery drain as putting the lead in the jack completes the circuit.

    As to whether this can be added to an active pre: generally the answer is yes. You have a dpdt switch (either a push / pull on a volume pot or a separate on/off mini switch), and when off the pickup signal will bypass the preamp.
    Here's an example from the bart website: http://www.bartolini.net/1_wirngs/ppapsw_t.htm

    Some situations where the answer is no:

    1) where preamp pots are mounted on a circuit board
    2) where an active blend is being used - such as j/u-retro and demeter preamps
     
  5. pjbasser

    pjbasser

    Sep 26, 2003
    Sweden
    Well
    If u don´t mind using another cable when ur goin passive, use one with a stereo jack in the end goin to the bass. Then u won´t make ur preamp active since that middle-ring wont start the preamp...

    Otherwise it´s a good idea to rebuild your amp and put 9-18v on that lug, and by using only stereo-stereo cable you don´t have to worry about batteries...


    Keep the funk alive!

    Peder:p
     
  6. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Well, it depends on the preamp and how it's wired.

    That being said, there's a couple of nuances to your question.

    If you're just talking about the battery, then I'd think that most active basses have this feature already built in, the preamp battery should be disconnected when you unplug the instrument. If this doesn't happen, it's trivially easy to add this feature into your existing circuit. (If your basses is 18 volt and uses two batteries instead of one, it may be a little more difficult, but still doable).

    The other nuance though, is do you want your bass to still work when you turn off the power? In other words, did you have in mind for it to revert to passive mode when that happens? 'Cause that's a slightly more complicated equation, then it depends on what kind of pickups are in there, and at the very least you'll probably have to add a special switch to reconfigure the circuit pathways to allow this to happen. With some pickups (like the low impedance kind), this would be virtually impossible and I'd say "don't bother". With others it might be a trivial modification. But also if you choose to go passive, be aware that you may experience some increased levels of hum and noise (relative to what you're used to and what you have now).
     
  7. coyoteboy

    coyoteboy easy there, Ned Supporting Member

    Mar 29, 2000
    Sactomato, CA
    The basic idea I had was a mute, kill, deactivate, no sound, no longer draining the batteries kind of pull pot. I know that, at least in the case of my Zon and forthcoming NSEU6, that the preamp is turned on by the cable contact, I was wondering if that ciruit junction could be moved to a different location, say a pull pot at the volume knob.
     
  8. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Yes, absolutely. You can move it to a "real" switch if you want to, either one that's on a pot (like pull-out, or even the old style "radio pot" where you click on before you turn the knob), or just a toggle switch or something.

    Usually on the ones that use the jack-disconnect method, there's a wire that goes from the preamp to the jack. They actually use a "stereo" jack, and they attach the power wire to the "ring" connection (the one in the middle, that isn't really there on a mono plug). That way when you insert a mono plug, the ring shorts against ground, and that way the ground connection is made to the preamp, turning it on.

    All you have to do in this situation is disconnect the wire going to the jack, and connect it to your switch instead. Then connect the other end of the switch to ground.

    That's all there is to it. Piece o' cake!
     
  9. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    Nice one nonsqtr, it's so obvious in retrospect yet I would probably never thought of it.
     
  10. rdhbass

    rdhbass

    Jun 28, 2003
    Springfield, mo
    I too am interested in installing a "Kill" switch for my emg's. I have left my jack plugged in twice and drained the battery. So all I have to do is get an "off-on" miniswitch and wire it up between the "hot" wire and output jack? Is this possible, I just wanna be able to turn it off and leave my bass plugged in... thanks.
     
  11. RyanHelms

    RyanHelms

    Sep 20, 2003
    Cleveland, OH
    If you're talking about passive pups w/a preamp in the signal, then yeah you can very easly do the ole' swap-the-power-wire-to-a-switch trick. Thing is though, power switching can invite noise, i.e. a loud "pop". A 1M pulldown resistor from signal output to ground usually fixes a noisy stomp switch, but I don't know about in an instrument. If it's a good preamp though, there should already be plenty of DC filtering.

    With some pickups (like the low impedance kind), this would be virtually impossible and I'd say "don't bother". --nonsqtr

    Do you mean pickups that are themselves active, that need +V all the time? I'm not hip to active pups, that's why I ask. Makes sense though.
     
  12. rdhbass

    rdhbass

    Jun 28, 2003
    Springfield, mo
    Yes, the pickups themselves are active. I am just forgetful and have left the darn thing plugged in without thinking. Thats why I wanted to see if I could get a "kill" switch installed.