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M-Audio EX-66 Active Speaker -

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    M-Audio EX-66 Active Speaker -

    Hello.

    Glad I found this forum since I really got started in electronics lately and from time to time I'm really kind of in dead end when it comes to troubleshooting a problem. So thanks in advance for every help.

    I have Problem with my Pair of M-Audio EX-66 speakers.

    I found a thread on this forum about these speakers that I will link here. I decided to start a new one because my Problem slightly differs and I wanted to keep it "clean" (https://www.badcaps.net/forum/showthread.php?t=33215)

    One of speakers just works fine. The other one has some kind of noise/hum. Its not very loud but still annoying. if you decrease the volume with the potentiometer on the back of the device, the hum gets louder. The more you approximate 0db the quieter it gets and nearly disappears.turning up the volume even more the general hiss gets too loud to really hear any hum. So I'm not sure if it may increase again.

    The other thing is that the lower the volume is set on both speakers the more the actual volume you hear will differ between them. With the potentiometer set to "0db" there is no difference. on "-40db" I increase the volume of the corresponding input signal from my PC about 10 db so they both match again.

    So what i have done so far. i swapped boards to see if the woofers were damaged but the problem swapped with the board.
    I checked for obviously bad caps but couldn't find anything. I cleaned of all the glue. There was a space on the board where it completely covered a big 100ohm resistor (unlike the board of the working speaker) that connected one pin of the potentiometer to the chassis. The glue got very solid there. It was cracked and inelastic.

    Since I don't have access to an oscilloscope at the moment. I was wondering what else I can do. Any suggestions what to check or what the problem i described could be?

    If you need further information, pictures or a sound sample of the hum please let me know.

    Thank you very much for all your help!

    #2
    Re: M-Audio EX-66 Active Speaker -

    yeah, i've come across some speakers that the glue had caused hum and crackling. but it seems you've cleared it.

    capacitors can be leaky or have a high esr without looking bad.
    is it 60hz hum from mains? maybe replace the main filter caps and any nearby the volume pot?

    does the low cutoff make any difference? that should help narrow it down a little. do also make sure there are no bad solder joints, such as: https://www.youtube.com/watch?v=fdfj7_czRcs

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