HeinoExpress Posted October 30, 2022 Share Posted October 30, 2022 Just repaired the LED in my FBV MkII Express. While probably a lot of different LEDs will work just fine thanks to calibration I wanted something close to the original design which uses an infrared LED (the photo transistor has its peak sensitivity at IR wavelength). Also, some older Line 6 pedals use a circuit with 5V and a resistor to protect the LED while others like my FBV MkII Express, the HD500 series etc employ a 3.3V circuit with FET and resistor (the LED is switched on by the main board). This matters because LEDs in the visible spectrum like the white LEDs recommended in some other posts have a much higher drop voltage (typ 3.1 V) than the original IR LED (1.5 V). Obviously this has quite an impact especially if your circuit is supplied by 3.3V because the white LED while emit with much less intensity (running at only approx 2.9V /4 mA with a 3.3V circuit) and not hitting the photo transistor's peak sensitivity. I picked this IR LED as the best match I could find for the original LT5K83-AA (typ Vf=1.5V, If =20mA, Po =18mW radiant flux over sphere): AREM-80C0-LM000 (Vf = 1.4V, If= 19mA in 3.3V/100Ohm circuit of FBV MkII Express). Works great. Other good IR choices according to the data sheets: Würth 15414185BA210 AREM-90C0-KL000 AA3528F3S (might have a shorter lifetime than the above due to higher thermal load). All of these were available at DigiKey. Even red LEDs should be a good choice and provide a better source for the original photo transistor than a white LED, such as: AA3528SECKT/J3 In summary: Luckily we have lots of choices for a replacement. Quote Link to comment Share on other sites More sharing options...
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