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 Post subject: LED specs?
PostPosted: Wed Dec 01, 2021 1:20 pm 
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Hi,
I recently built a few examples of the Spring reverb kit. With one of them I need to trouble shoot a non functional LED. I probably put it in backwards, and I already trimmed the leads on the through holes of the PCB so I imagine it would be easier to replace the old one with a brand new LED.
I do not have any spares and figure I should buy a handful of them to keep on hand, but I realize I have no idea if there are any specific specs or if all 5mm LEDs are pretty much the same. Should I be looking for some particular specifications?
It seems like a lot of vendors sell commodity packs of 5mm LEDs at really low prices. Are there any reputable actually-really-made-it manufacturers that make it worthwhile to spend more money or are all LEDs the commodity they appear to be?

Thank you!


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 Post subject: Re: LED specs?
PostPosted: Wed Dec 01, 2021 1:24 pm 
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There may be minor variations among LEDs from different vendors, but IMO it's not worth worrying about. All 5mm diffused LEDs are going to work basically the same, and all 5mm water clear LEDs will work basically the same. (The water clear are much brighter and will need a higher value current limiting resistor than the 4.7k that BYOC kits assume—since they use diffused LEDs.)

You can order from Amazon or eBay, but my advice is to order from a pedal parts supplier. For example, BYOC!

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 Post subject: Re: LED specs?
PostPosted: Wed Dec 01, 2021 8:18 pm 
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Thank you for the info.

FWIW, when I placed my order for the Spring Reverb kits I selected the optional Blue LED which happens to be clear.

Should I have swapped out the current limit resistor to another value?

It seems like the 4.7kOhm resistor limits the current between 1mA for 9vDC power and 3mA for 18vDC power, while most of the 5mm LED specifications I have looked at rate 20mA as nominal use. I assume the 4.7kOhm resistor is specified in the BYOC circuit so as to conserve power and there is little chance of a clear LED seeming too bright or burning out due to excess current draw.

I was hoping to learn that Blue LEDs selling for $1.75 are somehow made to a better quality specification than the packages of Blue LEDs that sell for as little as $0.02 per unit.

Thank you for the info.


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 Post subject: Re: LED specs?
PostPosted: Thu Dec 02, 2021 8:13 am 
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I can't speak to any of the electronics math you cite; I only think of this on a practical level. The clear blue LEDs look awesome and are a great choice. I doubt you'll burn it out with only a 4k7 CLR, but it may be very bright. I usually use a 10k for clear LEDs, mainly because I somehow got about 200 1/8w ones that I'm trying to use up.

If you're interested in messing around a bit, you could use some perfboard to make an LED tester. Put a battery snap or DC jack on there and socket spots for the CLR and LED. Then you can find out exactly how bright any give LED will be. I suppose you could even wire a pot in place of the resistor so you can get exactly the brightness you like and then measure the resistance. 8)

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 Post subject: Re: LED specs?
PostPosted: Thu Dec 02, 2021 9:35 am 
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Thank you for the additional info.


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 Post subject: Re: LED specs?
PostPosted: Thu Dec 02, 2021 3:57 pm 
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follow up:

I pulled out the non functioning LED, saw that there was a flattened indication on the lens, and confirmed that I had installed it with reverse polarity, so I soldered it back in place with the correct orientation and it works just fine.

I had assumed the leads were to short to work with but was able to assemble everything so it worked out ok.

Thanks again for the helpful comments.


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 Post subject: Re: LED specs?
PostPosted: Fri Dec 03, 2021 7:25 am 
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Glad to hear. Always good to salvage a part!

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 Post subject: Re: LED specs?
PostPosted: Fri Dec 03, 2021 2:22 pm 
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Johnny Schemaddict wrote:
follow up:

I pulled out the non functioning LED, saw that there was a flattened indication on the lens, and confirmed that I had installed it with reverse polarity, so I soldered it back in place with the correct orientation and it works just fine.

I had assumed the leads were to short to work with but was able to assemble everything so it worked out ok.

Thanks again for the helpful comments.


If you can't identify the flat side of the plastic lens (maybe it's gotten a little melted or damaged), you can also hold the LED up to a light and look at the inner parts. You'll notice one of the inner "guts" is larger and wider, while the other is smaller and thinner. There's a mnemonic that works here: "flat, fat, cat". The flat side of the lens and fatter side of the "guts" indicate the cathode (negative) side of the LED. This is a much more reliable method than the length of the legs, since there is not a universal manufacturing standard for which leg should be longer.

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 Post subject: Re: LED specs?
PostPosted: Sun Dec 05, 2021 10:19 am 
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Thank you for the detailed tips.

Regarding the current limit resistor value discussed above; I was test driving the pedals in a sunlit room and the brightness seemed ok. Last night I had one of the examples of the newly assembled pedals on a pedal board in a darkened room and when I looked down to adjust the knobs on an adjacent pedal the clear blue LED on my BYOC Spring Reverb nearly blinded me. The relative brightness was so much greater than all the other lights.

I think I will revisit the PCB and swap out to a higher value current limiting resistor. :-)

Thank you!


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 Post subject: Re: LED specs?
PostPosted: Mon Dec 06, 2021 12:02 pm 
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And now you know. :mrgreen:

Keep in mind the flip side of this, which is that "normal" brightness is often not enough on an outdoor stage during the day. Not for me, at least!

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