Wah Mod Done. Well Almost...

[CudBucket]

OK, so I finished the bypass/LED mod to my Rev. G Dunlop wah last night.  On the upside, it still works.  It wahs when it's supposed to and turns off when it's supposed to.  The only thing it doesn't do is light up the LED.  For the LED I used 24 AWG solid core wire because it's all I had.  I couldn't check for continuity because the battery in my multimeter died because I left it on.  I used a 2.2 K 1/4 watt resistor for limiting.  I guess I can try a lower value.  It's not that it's just dim because I shut off the light in the room and it's just off.

Anyway, I have one question.  It'll be stupid so bear with me.  I assume it's OK to clip the legs of the LED as necessary right?  Because that's what I did.

Anyway, I'm off to debug.

And thanks to all those who took time to answer my noob questions.

Dave

[CudBucket]

I think my problem may be the 2.2k limiting resistor.

According to the muzique.com calculator and the info on RadioShack.com (about the LED): I need a 274ohm resistor.  I put in 12volts for Voltage Supply value (since I'm not using a battery), 2.15 for the LED Forward Voltage (from the RS website), 36 for the LED current (36mA on the RS website).  It returns 274.  So tonight, on my way home from work I'm going to stop by RS and get a different resistor and see what happens.

Dave

[petemoore]

  2k2 should work, might be bright tho, I usually stick a 4k7 limiting resistor...then depending on how bright...end up with the 4k7.
  I don't think the 2k2 burned up the LED, this can be tested with the led/resistor across a battery, that's what I usually do...make an LED/R circuit and test it...noting with which polarity it lights, using the resistor as polarity marker [it's hard to see the LED's mark].
  If using a 3pdt switch, the LED wiring is the same as the test ^, except a lift switch [connection broken when SSw is in bypass mode], on a row of the switch 'unused for True Bypass'...then you have a PS/Switch/LED/resistor circuit, separate from the signal circuit, but sharing a row of the 3pdt used for bypass.

[CudBucket]

Well I did some testing regarding the dead blue LED on my wah.  I pulled it off the wah and with the 2.2K resistor still on, I tested it across a 9 volt battery (that read 9.46 volts on my MM).  No light no matter what polarity.  I thought maybe too much limiting so I tried it with a 470ohm resistor.  No good.  Then I tried a different green LED/bezel assembly I had and it worked with both resistors.

I then remembered the blue LED came two to a pack so I tried the other blue one.  It wouldn't work either.  I suppose I have to assume that both LEDs in the pack were bad.  Is this likely? 

Thanks.

Dave

[jonathan perez]

well, if you run an LED across a fresh battery, sans resistor, they will get fried.

the blues ones fry the best, and smell the worst.

i have a video demo of me burning a blue LED somewhere...if i find it, ill post it...

[RedHouse]

Ohm's law is your friend.

Since you have the "pack" the LED's came in, just look on it for the spec's and plug that into Ohm's Law.
(you can Google for the Ohm's Law wheel later, it's great stuff you will use a lot in this hobby)

We can use the V/I=R part of Ohm's Law, so say you have 9V and let's say the LED pack says it sucks down 20mA of current,

so:  9v / .020 = 450 Ohms

You would need a 450 Ohm limiting resistor in this case, now plug your actual numbers into this equation and feel good about the resistor you need.

{EDIT}
Never mind, I'm an idiot, and didn't read the above posts carefully, your numbers were 12v/36mA which would require a 333 Ohm resistor.

[CudBucket]

Haha!  No problem RedHouse.  I figured that even though Ohm's law tells me I need a 333ohm resistor, a 470 ohm resistor should work.  But no matter which one I used (470 or 2.2K), neither of the two blue LEDs that came in the same pack would work.  Now, I don't care about eating $1.29 on a couple of LEDs, I'm just trying to determine if I've done anything wrong.  For the record, the two green LEDs that came in the same pack work.  They're slightly different from the blue ones since they have their own chrom bezels attached and have, I believe 30mA values. So, 9v/.030 = 300ohms.  In this case, both the 470 and 2.2K resistors worked.

Go figure.

I'm going to pickup another two pack of blues today and see what happens.

Meanwhile, I'm waiting for a Red Fasel Inductor to come to continue my mods.

[David]

Hey, CB.  Not to sound like a smarta%*, but did you connect the LED properly?
On another note, with 9V, 1.5K limiting resistors have always worked pretty good for me.

[CudBucket]

Hey, CB.  Not to sound like a smarta%*, but did you connect the LED properly?
On another note, with 9V, 1.5K limiting resistors have always worked pretty good for me.

If you mean, did I put the resistor on the cathode leg, yes I did.  BTW, I'm only testing with the 9V battery.  My wah is a Rev. G with an AC jack and that's what I'll use for power.

Thanks!

Dave

[boogietube]

I just wanted to thank you Cudbucket, for posting that link to the wah wah mods in your previous post. Sorry you're having so much trouble. I've been wanting to mod my gcb-95 for some time now and couldn't figure the led thing out. Your post inspired me so I finished up that night.
I replaced the stock inductor with an Ariel FX halo , changed the sweep cap, vocal mod , gain mod,removed the buffer, true bypassed  and the blue led.  Had to replace the zener and the 1k to get the wires neatly in position.
All I can say is it sounds like a voice now. I can't believe it.
Thanks
Sean