So I want to swap out the red LEDs on my metal muff (I’ve been using it for about 7 years now – still works wonderfully) for a nice blue – hate red LEDs. I don’t know, however, if the voltage running the red LEDs in the circuit is enough to power the new blue LEDs I want to put in. The forward voltage on the blue LEDs I’m going to use is 3.0-3.2 V, but for red it’s typically 2.0-2.5 V. So, I’m not sure if the applied voltage in the Metal Muff circuitry is enough to power the blue LEDs. I imagine they use a 300 Ohm resistor or something with an applied 5 V, which would keep the current under 20 mA (around 17 mA to be precise – just the V = I*R equation) and power any 5mm LED I want to put in there while keeping decent efficiency but I don’t know if they run a voltage of say 2.5 V just to do it or keep people from tampering with the board.

Anybody know anything about the LED voltage in the Metal Muff board?

My guess is they use the 5 Volts I described but I can’t be sure. Please let me know if you have an idea what they’re doing in that black box of theirs.

Also I wonder if they keep the 9 V input throughout the board and use a 450 Ohm resistor, which would also work fine for me. It would be easy to step down the voltage with a voltage divider though, but I don’t see why they would do that just for the LEDs.

The equation to calculate a more accurate ‘R’ would be (V – Vf) = I*R though, where Vf is the forward voltage of the LEDs. So I guess they could use 9 or 5 V or what ever so long as they keep ‘I’ around 20 mA.

I also realized I need to know the resistance they use for the LEDs. When I change the LED to one with a higher Vf, the (V-Vf) becomes smaller, and if I use the same resistor, the current will drop, giving off less photons, so my LED may not be bright enough to see if it drops significantly far below 20 mA. So that is also a problem

*** Question Solved I Think: https://www.ehx.com/forums/viewthread/2867/ (Using This) ***

The current draw for the Metal Muff is 24 mA (Which is generally close Maximum without frying the diode).

They also probably keep 9V everywhere throughout the pedal for simplicity.

So the red LED lights ~1.8-2.2 V (Vf), so say (9-1.9)/.024 = 296 ; So I bet they use a 300 Ohm resistor.

A blue LED at ~3.0-3.2 Vf would give a current of ~19 mA. The brightness difference here is basically unnoticeable to the human eye. Even a current at 10 mA would still be pretty close to the 24 mA brightness as the current to luminosity ratio isn’t linear (so I read).

So it looks like putting in some blue LEDs will be perfectly fine, as long as you don’t mess up the board. Putting in any color 5mm LED looks fine actually, in case anybody reading this wanted to try it.