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Changing colour of LED power light.

Discussion in 'd.i.y.' started by Oneandtwo, Jan 13, 2022.

  1. Oneandtwo

    Oneandtwo pfm Member

    I want to change the blue LED on the front of the Linn Radikal to green LED to match the rest of my Naim system. Can anyone suggest what spec LED I need to buy? I am completely clueless regarding LED suitability!
  2. mansr

    mansr Objectionist

    Take a look at the existing one and pick something with the same physical dimensions. Since green LEDs have lower voltage drop (2.1 V) than blue ones (~3 V), you may need to also replace the series resistor.
  3. martin clark

    martin clark pinko bodger

    That;s entirely true; and also - practically - the green one won't be as subjectively as bright, so buy a green LED (NOT a 'high brightness' type!, something with a low mcd rating) and just drop it in place, I doubt any such series resistor adjustment is needed.

    Here is one source to peruse - pick a diameter/fitment to match what you need:{%22LED%20Colour%22:[%22Green%22]}

    If its just such a plain 3 or 5mm green you need, close ot Naim colour, I can spare a couple to you free by post... pm me an address.
  4. Oneandtwo

    Oneandtwo pfm Member

    The blue one is too bright anyway, I’ll pop the case off this weekend and see what dimensions I need.

  5. earlofsodbury

    earlofsodbury Wastrel.

    Making some generalisations here because I've not dismantled a Radikal -

    How you proceed depends on how the current LED is mounted. With a bit of luck it'll just be glued to a hole in the faceplate with hot melt or tape and have a flylead connecting it to the main PCB. If not, you've a bit more dismantling to do.

    Unless it's already printed on the PCB, I'd suggest you first very carefully check voltage and polarity of the existing LED in-situ then match the replacement accordingly. You need to get it in the right voltage range as most LEDs will only give you their rated light output within some tenths of a volt of specified value, and obviously polarity is important.

    For a typical green LED I'd guess you're looking at Vf ~ 2.2, wavelength ~ 560nM, and intensity ~ 3 to 20mcd if you want something that's subtle.

    The new LED's leads will be unequal lengths, the longer is the anode.

    If there's a lot of hot melt, use a hairdryer to soften the glue first, saves damaging anything while dismantling.
  6. mansr

    mansr Objectionist

    Sorry, but that's not how LED voltages work. The voltage drop across a LED (or any diode) is constant once it is fully conducting, the amount determined by the wavelength of light emitted. If the per-photon energy is expressed in electron-volts, that is also the voltage drop. When connected to a fixed-voltage source, a current-limiting series resistor is required. Supposing the blue LED has a 3 V drop and is driven by a 5 V supply, the voltage across the series resistor will be 2 V. Substituting a green LED with a voltage drop closer to 2 V, the current will increase by nearly 50% which might be too much. You need to check the rated current of the replacement LED and work out a suitable resistor value to go with it. Limiting the current to less than the maximum simply reduces the brightness.
    earlofsodbury likes this.
  7. Mike Hanson

    Mike Hanson Lovely!

    Yeah, LEDs can be quite a hassle to get the right inline resistor. I usually start with a very large value (e.g. 100K or higher), then work my way down until I get to a suitable brightness.
  8. 337alant

    337alant Negatively Biased

  9. earlofsodbury

    earlofsodbury Wastrel.

    Quite right of course, I really should refrain from answering DIY threads after 2 sleepless nights...
  10. Oneandtwo

    Oneandtwo pfm Member

    I have had a quick look inside and the led appears to just be pushed into a holder in the front panel. It is attached to the main circuit board by a lead and plu so should be easy to swap around.
    Mike Hanson likes this.
  11. russel

    russel ./_dazed_and_confused

    Some green LEDS have started to use phosphor to generate the required wavelength and have a higher voltage drop.
  12. david ellwood

    david ellwood Kirabosi Kognoscente

    I’d simply disconnect it, and avoid any potential warranty problems.
  13. mansr

    mansr Objectionist

    I didn't know that. What is the advantage of this approach?
  14. russel

    russel ./_dazed_and_confused

    I suspect it’s for a broader spectrum or dual spectrum as they were recommended for measuring pulse.

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