High Output LEDs

[samrsmiley]

I'm attempting to build a tubescreamer, rangemaster, and OD250 clones (already breadboarded them, but yet to add LEDs) and was wondering if I need to add different resistors or circuits to get the high output LEDs to light up.  Looks like you mainly use a 4.7K resistor before the LED, but do high output lights change what you need resistor-wise?  Also can you swap out these high output LEDs in mass-prod pedals (BD2 and Maxon OD808), or do I need to change things there too?  I'm pretty new at this stuff, so if you could give me an explanation that would really really helpful!  I know it probably has to do with ohms law, and voltage drops... but not sure yet how to figure it out in a practical sense.  Thanks!

[foxfire]

different places sell different leds so your best bet is to just try it. start with 4.7k. most likely you'll blind yourself. i generally end up with somewhere around 10-15k. as for retro fitting new leds in old pedals, again it probably won't hurt to just go for it. unscientific i know but, it's how i learned.
rylan

[remmelt]

I usually just take a 10K pot and wire it in between, then dial in the "right" amount of brightness. Measure the pot, put in the nearest resistor value.

[darron]

good question. the super bright LEDs are often so because they have a much more focused viewing angle, so the light doesn't disperse in all directions. to protect the LED you can use the save low values resistors, which is pretty much anything over 1Kohm. So then the question comes to how bright you want it. Since the super brights are actually brighter, you can increase the resistor values and get a similar brightness. Will you run off battery or power supply? If off power supply you may as well have them as bright as you can get them without blinding you. With the 3mm vlear to blue LEDs that I used to use they were so bright that a 56K would be good enough to have them clearly visible in day and night, but that was with the intention of someone possibly using a battery one day instead of a power supple.

[Guitarfreak]

Sorry to bump this super old thread, but I am trying to replace the LED in my OD808 with a super bright and I've already had one burn out a few minutes after installation 

I can't seem to find the bias resistor and can't seem to find a good schematic which gives an R#.  I've attempted to trace it back and can't find a resistor on the immediate path which has a value which would say to me "LED bias resistor!" or whatever that means 

[Guitarfreak]

Ok, as an appendage to my previous post I have found that the LED still functions and is not burned out...yet.  It lights for a few seconds before fading as though it has burned out.  If I turn off the pedal and wait for it to cool it relights before repeating the process.  I have found what I think to be the LED bias resistor which reads 3k3.  What does this problem sound like?

[PRR]

Try a fresh battery.

[Guitarfreak]

Try a fresh battery.

It's powered by a Voodoo Labs PP2+

[jkokura]

Have you got the sag on? Double check with output you're using with the PP2. Is it just an LED issue, or is the pedal not working right?

Jacob

[Guitarfreak]

Have you got the sag on? Double check with output you're using with the PP2. Is it just an LED issue, or is the pedal not working right?

Jacob

The sag control is cool! 

alas, the I am not using a sag input.

[darron]

Try a fresh battery.

It's powered by a Voodoo Labs PP2+

try a fresh Voodoo Labs PP2+.... jk




leds can be damaged and half work.

as long as you have a limiter resistor of around 1k or greater and only feed it around the 9v,12v etc range you should be fine in all circumstances.

i'd replace the LED and put in another resistor of 1k just so you can be sure that you are doing the right thing. even if you think you had 3k3 then +1k makes it a safe 4k3.

[PRR]

> lights for a few seconds before fading

The OD808 uses an odd technique for the LED which makes it *very* sensitive to power voltage sag.

Where a normal LED feed will go half-bright when battery sags to 7V, the OD808 LED will go dark.

It may have done this before; or you may have upset a connection or joint while you were working.

The sag may be slow-down and slow-up due to large filter caps.

[merlinb]

The OD808 uses an odd technique for the LED which makes it *very* sensitive to power voltage sag.

Is it this circuit?
http://www.matsumin.net/diy/bunkai/od-808/OD-808_sch.BMP

That 5.6V zener doesn't appear to do anything useful. Surely getting rid of it is the answer?

(EDIT: Actually this circuit has a lot of unecessary parts, so perhaps it's not the right one).

[darron]

The zener in that schem looks like it is there to intentionally fade out the led on a dying battery.

[earthtonesaudio]

Your new MEGA BRIGHT LED probably has a higher forward drop and so there's not enough voltage for both it and the zener diode.  In other words the circuit "thinks" the battery is dead, even when it's not.

Short/remove the zener and prepare for early onset blindness.

[Guitarfreak]

Could I also mod the value of the resistor to a lower one or would removing the diode be the best option?  It is connected in series so would I need to jumper it?

[amptramp]

Remove the zener diode and increase the resistor value or you will need one of the items on this page:

http://hoodlum-welding.com/hoods.htm

Come to think of it, that would look awesome at a gig until you lost sight of everything else and fell off the stage.

[Guitarfreak]

Updates.

Removed diode: no LED lighting

Jumpered diode: LED lighting, still dies.

[darron]

is it as per the schematic that merlinb listed or not?

[Guitarfreak]

is it as per the schematic that merlinb listed or not?

It looks like the general gist, but I don't see any transistors in that schematic and there are 6 on my board.  The LED circuit does not come straight from VCC as that schematic would imply, it comes from the base of one of the transistors.