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High Output LEDs

Started by samrsmiley, August 12, 2008, 11:01:25 PM

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earthtonesaudio

Am I correct in assuming your pedal has an electronic bypass?  Meaning, it contains a couple BJTs wired as a toggle flip flop and perhaps some JFETs for switching?

If that is the case, it seems likely that you've wired the LED either backwards, or to the wrong point on the flip flop.  When you hit the switch, a pulse of current goes through the FF that toggles it, but it may also exceed the supply voltage.   If your LED is backwards it would light very briefly upon switching and then die.  I think it's possible that you'd get the same behavior if you connected the LED to some other point in the FF circuit, such as the base of one of the transistors.

The proper location for the LED in such a circuit is in place of the collector resistor of one of the transistors.  That is, it goes between collector and V+.

Of course if your pedal is mechanical bypass ignore all of the above.  I have no idea what's wrong. :)

Guitarfreak

Interesting idea.  I tried flipping the LED and got a slight flicker when switching, didn't even last the few seconds that it did in the other orientation.  Sheesh.  I'm waiting on a smaller value resistor to arrive so hopefully that will do the trick.

merlinb

If you actually provided us with a schematic then this problem could be fixed in about two seconds without any 'random component changes'.

Guitarfreak

Quote from: merlinb on September 27, 2010, 09:36:56 AM
If you actually provided us with a schematic then this problem could be fixed in about two seconds without any 'random component changes'.

Well that's the real trick then isn't it.  I haven't been able to find a schematic under the name of Maxon OD808 which I could say accurately describes the pedal PCB.  I think the Tubescreamer 808 schematic is the most accurate that I've seen.  I've heard that they aren't identical circuits though.  You should probably go off of that anyway.

http://www.schematicheaven.com/effects/ggg_ibanez_ts-808_ORIGINAL.pdf

Guitarfreak

Well I have news, apparently now the LED is remaining lit without problem.  I haven't done anything but let it sit unused for a while (I've been busy).  Anyone ever hear of a shy LED?

amptramp

Maybe shy of a little bit of flux on the solder joint.

Guitarfreak

Quote from: amptramp on September 30, 2010, 09:29:32 PM
Maybe shy of a little bit of flux on the solder joint.

Oh I flux it.  I flux it hard!  :icon_lol: