Emu XL-7 & MP-7 User's Group

Today i took a day off from work because i had certain bowel problems that i prefer not to detail in here :) So i took the XL-7 to my bed, put my headphones on, and there it was: that annoying 60hz rumble that comes from the headphones output. It was so loud that i couldn't focus on making music.

So, as i had some free time, i took my swiss army knive and opened the damn xl7. What i found, first than anything, is that the XL7 has a pretty neat inside design. No clutter or messy cables anywhere; in fact it is easier to disassemble than my PC. So i took the headphones board apart. It's a little one, that includes the volume knob, the on/off button and the headphones output. 

The headphones output has a tiny metal border that makes contact with the XL7's metal case. But then i figured out that the metal case is spray painted. There was paint around that area, so the headphone socket couldn't make contact with the case. I took my knive and peeled the painting from the inside in order to reveal the underlying metal.

Then i put everything back in its place but i didn't attach the screws to keep the XL7 assembled. I plugged the xl7 to test it (remember to unplug everything everytime you are working with it unless you want to test the unit ! shock hazard !)

But the humming was still there. I realized that when i moved the top part of the case and changed its position in relation with the lower part of the case, the humming varied its amplitude. In certain positions it almost dissapeared.

What i found, is that there are a couple of strips in the front and in the back of both case halves that don't have paint at all. The metal is exposed there. The builders relied on the contact between both halves in order to close the grounding circuit.

The circuit (i'm not electrician at all) goes like this:

headphone socket -------> upper part of the case -------> lower part of the case ---------> power supply casing -------> ground.

However, if the contact between the upper part of the case and the lower part of the case is lost by any cause, the ground circuit remains open, and what you get is that upsetting noise.

When i touched the naked strips of metal, i realized that they were sticky. The metal was visible, but it seemed rather opaque. I thought that it could have become sticky during the painting process, i guess that some adhesive tape or something else is used to cover the zone and then it must be removed later.

So i took again my swiss army knife, and started scratching the exposed metal strips on both the front and the back of both halves of the case. You must do this process by putting the unit upside down to avoid tiny metal debris from falling inside the unit (you don't want to short circuit your XL-7 !!!). I blowed into the unit to make sure that no metal parts were falling inside.

On scratching the metal, the shiny aluminum was revealed. It was very different from the rather opaque aspect it had before. I cleaned the strips to make sure that no metal debris was left, and then i reassembled both halves and attached the screws firmly.

So i plugged the unit to the mains, turned it on, and...




Voila ! the humming was gone !!!

Now i can use my XL7 everywhere... even at bed :) And it doesn't hum at all. Amazing that this hasn't occured to me before. 

I'll paste this solution in the files section, so it can be of help to other XL7 users.

Cheers,
Jose Saez AKA Nemmo (www.taliesin.cl)

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