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Adding a LED to an active / passive switch ?

Discussion in 'Pickups & Electronics [BG]' started by matt8602, Dec 10, 2017.

  1. matt8602


    Dec 12, 2009
    I'm currently installing an OBP-3 in a new project bass with an active / passive switch (or actually, it's more a preamp bypass as the pickups are active EMG's). I'm following this diagram:


    I would like to add a LED on the DPDT switch, as an indicator when the preamp is ON.
    Can someone told me how to do / or edit the current diagram ?

    I'm also planning to put a 6.8k resistor to reduce power consumption from the LED. Does this sounds good ?
  2. You'll need another pole on your switch, otherwise the power from the battery will go straight to the preamp's input (not good).
  3. matt8602


    Dec 12, 2009
  4. exactly
    Last edited: Dec 10, 2017
  5. matt8602


    Dec 12, 2009
    Thank you.
    Will this work ?

    3PDT wiring 1.
  6. SteveCS


    Nov 19, 2014
    Hampshire, UK
    6.8k at 9V will barely light the LED. Proceed as follows...

    Get the Forward Voltage and Operating Current of the LED from the spec sheet. Say for example 2V at 20mA. With a 9V supply your resistor needs to drop 7.0V (9 - 2) at 0.02A. Use ohms law..

    = 7.0/0.02
    = 350ohms.

    Hope this helps...
  7. This is usually not agood idea. LEDs draw a lot of current, in fact much more current than your bass. You will be significantly reducing your battery life to keep the LED glowing.

    If you must have an LED, consider a low current flashing LED. Those wont reduce your battery life as dramatically as other LEDs.
    Flippy and FugaziBomb like this.
  8. matt8602


    Dec 12, 2009
    Thanks for the advices. I will try different LEDs and resistors and see if it's worthy or not. by the way, will the diagram I posted above will work ?
  9. The diagram will work.
  10. matt8602


    Dec 12, 2009
    Good, thanks!
    By the way, what's the real deal with low current leds ? Is there a big difference compare to a standard or high intensity led wired with a higher resistor to match low current led consumption ?
  11. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    why bother with the LED in the first place? you have EMGs, which means the bass is "active" whether the preamp is kicked in or not.

    if you can't tell from the sound whether the preamp is engaged why bother using it at all?
    FugaziBomb likes this.
  12. matt8602


    Dec 12, 2009
    I can tell a difference ! I think you misunderstood. As said it's a true bypass and not an active / passive switch as the bass is active anyway even with the preamp out. I like having both options to use the EMG's on their own with the active tone pot associated, which act different than the treble on the OBP-3. It just gives more tonal options and for example, I like having the mids cuts on the OBP-3 and do a quick switch on it just for slap parts, etc. The LED might sounds like a fancy stuff, but in live condition it helps avoiding confusion when you have 2 toggle switches close to each other.
  13. Wfrance3

    Wfrance3 Supporting Member

    May 29, 2014
    Tulsa, OK
    The light seems good, but active up passive down on a toggle works. Or the reverse if you like...
    Besides your ears can tell.
    Spidey2112 likes this.
  14. FugaziBomb


    Jun 5, 2017
    I went down this same road years and years ago only to find that the LED was a useless drain on my battery. Good luck...
    Killed_by_Death likes this.
  15. Ductapeman

    Ductapeman Ringmaster and Resident Geriatric Gold Supporting Member

    Feb 7, 2016
    The West Pole
    I am not a crook
    Years ago, when LEDs first became common enough to buy at the local electronics supply (1973?4?) I picked up a couple and, having room under the pickguard of my Jazz Bass, wired two of them into my pickguard, yellow and red, on a switch connected to a battery-- not connected to anything else in the bass, just a couple of lights. Great big old toggle switch, very obvious-- I labeled them "STUN" and "KILL," and when I started digging into a part I'd flip it to "KILL," and later everyone wanted to know what I had done to make my bass so much thicker when the red light came on--
  16. SteveCS


    Nov 19, 2014
    Hampshire, UK
    Indeed. Even in an ideal linear world a 20mA LED with a 10mA preamp equates to almost 70% reduction in battery life. In reality probably even worse... Personally I wouldn't bother.
    Ductapeman and nbsipics like this.
  17. Ductapeman

    Ductapeman Ringmaster and Resident Geriatric Gold Supporting Member

    Feb 7, 2016
    The West Pole
    I am not a crook
    Oh, but they're so much fun-- did you see the LED/fiber optic job that Mike Lull did on Roger Fisher's Strat? Looked like the fretboard was on fire-- it had a pretty hefty battery in it though as I recall. I've been toying with a Roland Midi setup with the 13-connector cord, and I now think that paralleling (?) a phantom-power line with the regular cord would be less fuss and would open up a lot of options-- have a couple up my sleeve myself, but have lost my work bench for a while--
  18. FunkHead

    FunkHead Supporting Member

    Mar 10, 2007
    Maybe a relay and separate power supply would work??
  19. Spidey2112


    Aug 3, 2016
    Keep it simple... life is hard enough, as it is...
  20. Flippy


    Jun 9, 2017
    Like a battery?

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