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Last question: How can I wire an LED into my 9v active bass?

Discussion in 'Pickups & Electronics [BG]' started by Fender32, Oct 6, 2013.

  1. Fender32


    Jun 23, 2005
    Kent, England
    I'm afraid that I've been asking for rather a lot of help in this part of the forum recently, but this is the very last question ... I promise :smug:!

    The situation is this;

    I have recently modified an active bass guitar by replacing the pickup, removing all of the previous circuitry and starting again from scratch. As it stands, I have all of the controls functioning exactly as I wanted them to and tonally speaking ... life is good :p!

    Just one, niggling issue remains :meh: - the bass has an LED installed, which used to illuminate when the (previous) active circuit was engaged. It was wired to a PCB, which is no longer part of the electronics. I have to find a way to power it with what is left :meh:.

    The bass now runs permanently in active mode, so I don't need any kind of switching on the LED. When the bass is plugged in, I want it to illuminate and when the jack is unplugged, I want the LED to go out again. Simple!

    The bass has 9v electronics and a stereo jack. The questions are; what value of resistor do I need for a 'normal' guitar LED in a 9v circuit and most importantly, how should the LED be wired in?

    Diagrams would be great, if anyone can oblige ;), but all comments are welcome. I've tried searching the forum already and when I Googled it, I could only find threads where people wanted complicated switching or wanted to LED to act as an indicator of battery life etc. Nothing that applies to my situation.

    I hope that someone will be able to help me sort this, as it is the final piece in the jigsaw puzzle and then my 'dream bass' will become a 'reality bass' :p!

  2. JustForSport


    Nov 17, 2011
    First, the resistor req'd is dependent on the LED color desired (and I'm not sure which is req'd with which color),.
    Second, I'd add a leg from the batt + to the ground leading back to the jack (switching terminal).
    Check continuity of circuit first so that plug insertion will complete LED circuit.
  3. Fender32


    Jun 23, 2005
    Kent, England
    Ah, sorry, didn't realise that colour played a part :meh:. It's a yellow LED.

    I'm sorry to say it, but I'm a bit of a dunce with all things electrical, so I'm not sure what you mean by 'a leg parallel to the ground leading back to the jack' :confused:!?

    Is there any way that you could explain as though you were talking to a 5 year old, please :D?
  4. Fender32


    Jun 23, 2005
    Kent, England
    Maybe I should invest in one of these kits - it has a 'beginners guide to working with LEDs' included in the price :p ...

    eBay link ...
  5. michaelandrew

    michaelandrew The bass player is always right.

    That kit could be an excellent investment: LEDs are fairly easy to deal with. First, Ohm's Law;

    I=V/R, V=IR, R=V/I

    Where I is current (Amps), V is voltage (Volts), R is resistance (Ohms).

    Most LEDs will take about 20 milliAmps, or 0.020 Amps (depending on size and colour, check the LED specs), so, for a 9V battery:

    R = V/I = 9/0.020 = 450 Ohms

    That's a conservative value that doesn't take account of the voltage drop across the LED (about 2V). Start will a larger value resistor, say 560 Ohms and see whether you get the brightness you want. A smaller resistor will give more brightness but reduces battery life, too small a value could damage the LED. Have a look at http://ledcalculator.net/.

    The LED will have a (+) lead and a (-) lead (on new LEDs, the + side has a longer lead). The (+) side of the LED goes to the positive (+) battery terminal, the other side goes to one side of the resistor and the other side of the resistor goes to ground (the negative (-) battery terminal). It doesn't matter which way 'round you have the resistor.

    Get the kit and a spare 9V battery - worst case you might burn out a few LEDs, but you'll learn a lot and it's kinda fun.;)
  6. Fender32


    Jun 23, 2005
    Kent, England
    Thanks for the insight, Mike :)!

    Actually, I have already ordered the kit :smug:. I figured that I was going to need at least a couple of the components in there and may well decide to change the colour of the LED in the future (if I replace the current gold hardware with black, for instance ;)), so it's worth having. Besides, with postage costs, even a single resistor would cost a pound!

    I just have to figure out how to tap into the 9v power running through the active circuit, without affecting the sound :confused:. Maybe I should put my volt meter to use, as just staring at all that 'spaghetti' is getting me nowhere :D.


  7. GrumpiusMaximus

    GrumpiusMaximus I've Seen Things You People Wouldn't Believe

    Mar 11, 2013
    Kent, United Kingdom
    Nice to see another Kentish bloke in a shed with a soldering iron!
  8. BassGyver


    Jun 29, 2004
    Get an "high intensity led", et run it with a lower current than 20mA. Your battery will last much longer...

    I use very high intensity blue leds as low as 0.2 microAmp, with enough brightness to use as a power indicator.
  9. The voltage is not 9V, it's the supply voltage minus the load voltage, which would be around 6V for the average LED.
  10. JustForSport


    Nov 17, 2011
    Here's a sketch from a Hohner BBass VI that you may find useful...

    Attached Files:

  11. Fender32


    Jun 23, 2005
    Kent, England
    A shed :eek:!? I can barely afford the rent on my tiny flat, let alone having enough wealth to also own a shed in Kent :D.

    Good tip, thanks :)!

    Good point, l6m. However, this may not apply in my case (read on ;)).

    Thank you for that, JFS :). I could kind of follow it, but I have come up with a simpler solution to the problem (I think) :) ....


    I forgot to mention something in the OP, which might have made things more simple :bag:.

    The bass originally had 18v active electronics and therefore ... two 9v battery holders. I'd only been using one battery, to keep the voltage at the right level for the new (9v) pre-amp, but it occurred to me last night that if I were to re-wire the second battery to be independent of the first (is that what you call switching from series to parallel wiring :meh:?), then I could have my own dedicated circuit for the LED and not worry about where to interrupt the power supply to the tone circuit :).

    I did that this morning and it worked! I had one battery for the active EQ and another, which was dedicated to supplying 9v (8.24v, according to the voltmeter ;)) to two 'virgin' wires (independent of the rest of the wiring). The next stage was to try and find a way to work the negative wire into the stereo jack socket, so that the power would only flow when a jack was inserted. That part was, with the help of the voltmeter, pretty easy :).

    So, as things stand, I have exactly what I need in order to go forward to the next stage. I have 9v of power going to two (currently) unattached wires, but only when the jack plug is inserted :hyper:.

    The final stage then, will be to just find the right combination of resistor and LED and solder them in between the '+' and '-' wires. How hard can that be :D!? As I said earlier, I have ordered a kit with about 50 resistors and LEDs and (most importantly) an instruction book on how to wire them up, so I reckon that the final part should be easy.

    Once that's done, my modifications to this bass will be complete and I can sit back and enjoy playing it. In all honestly, I bit off a little more than I could chew when I decided to strip out the electrics and start all over again with this bass, but thanks to all the TB members who've contributed to my threads, I have been able to get through it and succeed. God bless you all ;)!

  12. michaelandrew

    michaelandrew The bass player is always right.

    Correct. That's why my reply says:

    "That's a conservative value that doesn't take account of the voltage drop across the LED (about 2V)."

    It depends on the LED type. Looks like the OP is pretty well sorted now though. ;)
  13. bassbenj


    Aug 11, 2009
    I have LEDs on some of my basses and they are way cool! HOWEVER, they hog current and will run 9 v batteries down pretty fast. For this reason you are absolutely right to wire a second battery. That keep the bass playing when the LED drains the battery! Also try to keep the LED current drain as low as you can. Try to use a high intensity LED which is to say one as bright as possible for a given current. Older LEDs can operate on up currents in the range of 20 milliamps. A modern "bright" one [I like to use some ultra-bright blue ones from Radio Shack] are really decent with just a couple of milliamps.

    The key is to not worry about actual specs (unless you have them (See for example Mouser with ratings of brightness and current) ) but simply experiment. Start with a high series resistor (like 10K and work your way down until it's bright as you want. Try to pick the LED and resistor values that gives the most light for the least current.

    In my case the basses are usually powered over a stereo cable and I have them wired so the LEDs only light with external power. If you use a battery they do not light to save the battery. My next thing is to power the fretless neck LEDs from the external power.

    Good luck!
  14. Fender32


    Jun 23, 2005
    Kent, England
    Thanks for the input, bassbenj, I shall keep all that in mind and experiment with the different resistors and LEDs in my kit (when it arrives) :).

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