Apollo Trem & LED Brightness

[Anonymous]

Hi folks,

I’m relatively new to pedal building, but I’m starting to get my head around the concepts.

My question relates to the Apollo Trem and LED brightness. I’ve used a purple LED for my build (with pulsing LED), and the LED is quite dim. My instinct would be to lower the resistance of the CLR, but in the case of the Apollo circuit there isn’t a clear CLR to my inexperienced eye. Taking a look at the schematic, might I achieve a brighter LED by increasing the value of R11? Or am I completely on the wrong track? Would love any advice.

Cheers

Edit: I should be clear, I’m not using the 3PDT breakout board on this build. The LED is wired directly to the main board.

[Playsforfun]

Hello Alistair. Up front I will tell you that I don’t understand the circuit completely. But focusing on the led choice color, it seems from what I read that purple just doesn’t have the ‘luminous intensity’ of some other color choices. I think you chose a dim color as far as led’s go. If purple has got to be the one then I would suggest a white led with purple dome. Hopefully for complete understanding, someone smarter than I will pop in below with the science behind it all. I only chose purple for a build once and had the same problem but because I wanted only purple I settled for dim. It worked out for me with a happy customer though.

[Billy]

Current determines how bright your LED is

As pff says it may well be your LED colour choice purple is a higher forward voltage around 3.6v and depending on the type UV, super bright etc may require much more current than your average 20mA for standard LEDs

Some purples need as much as 30mA to 40mA and beyond

The fixed CLR would be R10 the 330R in conjunction with the depth pot, R10 is obviously there when depth is set to 0 ohms CCW to make sure there is still some current limiting resistance protecting your LED

You may well be able to reduce R10 but would need to know the current rating for your LED then it’s just a case of a quick ohms law calculation to determine your CLR value or use a calculator like this

https://www.allaboutcircuits.com/tools/led-resistor-calculator/

The LED is part of the LFO circuit but changing R10 will not affect it

Whether or not it would be significantly brighter I don’t know, as it is with your depth at zero and R10 330R your current would be around 20mA dropping R10 to 220R would be around 40mA

First you need to know your LED current rating so you don’t burn it out

Also remember resistors have a tolerance rating metal film + or – 1% carbon 5% so a 220R metal film will range from 217 to 222 ohms carbon film 209 to 231

Pots have a 20% tolerance and it’s very unlikely it would be 0 ohms turned all the way down at the very least it’ll have a few ohms on it

Important if you’re getting near to your CLRs value limit

Use your meter to check resistor value to make sure it’s within the required range

[Anonymous]

Wow, awesome replies. My thanks to you both. It seems as though it may be easier to try and source a white LED with a purple dome (unfortunately the final colour is important to my aesthetic goal).

Billy that’s not to say your response wasn’t useful. You prompted me to go and read up on what diode forward voltage meant in practical terms. I think I have a much better understanding. So thanks again.

[Author]

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