When I wire up LED I get a constant high pitch noise?

[daryl]

Just testing a BIG Muff pedal based on the GGG diagram:

http://www.generalguitargadgets.com/pdf/ggg_bmp_wiring.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
http://www.generalguitargadgets.com/pdf/ggg_bmp_vram_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

It works fine apart from when I wire up the LED It makes a constant high pitch noise? Remove the led and it works fine.

Anyone got any ideas? Bad Led?

[armdnrdy]

Did you try moving the LED wires away from other wires?

See this post:
http://www.diystompboxes.com/smfforum/index.php?topic=100099.0

[Kesh]

can you change the pitch of it with the sustain or other controls?

[daryl]

No the pitch stays the same no matter what you do with the controls.

[R.G.]

It's highly unlikely to be the LED. It's much more likely to be power supply impedance or wiring issues that the LED current drain is bringing out.

How's it powered? Battery? DC adapter? If there's enough voltage and current available and the wiring isn't too bad, a BFC across the +9V and power on the PCB might fix it. I'd try 100uF to 1000uF, paralleled by a 0.1uF.

If it's a too-saggy power supply or a bad wiring issue, that might not be enough. There could be other causes as well. I'm just guessing based on the post. Without more specifics, it's quite difficult to say, other than a standard LED cause that on its own.

[daryl]

It was a bad LED, put another one in when I got it back to my house this afternoon and all is good.

Put the old one back in just to make sure and sure enough it came back.  So just a bad LED.

[R.G.]

That's unexpected. Can you provide any more info? I'd like to understand how that happened.  It's that curiousity thing. 

[daryl]

The led's have been in my garage for a long time, I can only think that it somehow got moisture in it or wan a manufacturing defect??

[alparent]

Send the LED to R.G. so he can satisfy is curiosity!
And it might be profitable to all of us in the future.

The more R.G. knows ............... the better off we are all!

[PRR]

There are now LEDs with "flasher" chips inside.

*Maybe* if driven with a large resistor, they try to flash much-faster than designed?

I agree with R.G. The basic LED is a pretty tame and robust device. One of the few Silicon thingies which almost-can't do anything exciting. And isn't too likely to absorb water. So I too am very curious.

[daryl]

I'll see if I can find it in the trash tomorrow and triple test it.

[R.G.]

Right.

The pinnacle of weird stuff I ever saw on ordinary LED do was to be fed by a uC which would turn it off and then use it as a photodiode in the few tens of microseconds it was off to sense light. But even then, the LED was dancing the uC's tune.

I suppose an internal arc could do something like this, but I'd expect more random noise. My initial thought was a feedback reaction to some kind of power supply issue where the power shut down with the extra LED current, turning off the LED, which let the power supply come back up, which...

I suppose there could be photosensitivity on some of the other parts in the circuit, but I would not then expect a replacement LED to be different.

So I'm mystified. Never seen an oscillating LED before.  

Mother Nature is whispering to us. Just can't make out the words yet.

[Kesh]

LEDs work as narrow band photo detectors. It's called the Mims effect.