You had lined all the mdf box inside with foil??
Then you have a 18 mm gap due to the MDF thickness...
the idea is put a rigid metal plate directly on the back of the amp plate, to close the top of the "u", electrically connect that plate trough to the metal of the amp plate ( scrap some paint if necessary, you want some good contact here.
Be safe!!!! Watchout you do not short anything!!!! There is mains voltage inside!!!
( edit) : for safety, It's better to put a plastic isolation sheet between the plate and the amp plate , leaving the electrical connection just on a small surface-
A clip holding the foil in place with some pressure where the foil electrically contacts the amp will be sufficient for this temporary test set-up.
Also the slits for ventilation on the amp plate are as many antenna's as you can dream of, so maybe if a) does not work try cover the whole thing. Be warned ventilation is going to be inexistant, so <watch any sign of overheathing, this is just a very temporary troubleshooting
Problem solved?
Then it's time to think of a more permanent functional ( safety/ventilation wise and aesthetics) solution
IF not,
Found this on a forum, a Behringer rep said :
“ RFI problems are always tricky to diagnose and cure. The first thing that I would try is to slightly move your speakers. Doing this will sometimes block the problem frequency and fix your problem. If that does not work I would try out a UPS (Uninterrupted power supply) and these can be purchased at your local computer store. The one you would want to look for would include an RFI filter. Proper grounding will help, also avoiding ground loops. Is there a computer monitor or other CRT-type device close by? If you turn it off, does the interference go away? Try a 2-prong to 3-prong adaptor briefly - does the RF go away? Sometimes it's carried by the ground lug. Try to eliminate any kind of ground loops by connecting your devices to one outlet.
We hope that we have been able to help you with this information. If the problem persists, feel free to contact us - we're here to help!
Best regards,
Your BEHRINGER Customer Support Team"
Try what they suggest . also You could start with ferrites right after the IEC inside the amp. I think it's not necessary to go and buy an ups just for a RFI filter, you could roll your own, provided you are a bit handy with soldering irons and oblige to safety ( especially while working with potentially lethal mains powered voltage).
PS: Also try to make a diy mains cable from Belden 19364. Earth the shielding of this cable on the wall socket side ( not the speakers side). If this does not help the FM, it will help boosting sound quality very effectively.
Then you have a 18 mm gap due to the MDF thickness...
the idea is put a rigid metal plate directly on the back of the amp plate, to close the top of the "u", electrically connect that plate trough to the metal of the amp plate ( scrap some paint if necessary, you want some good contact here.
Be safe!!!! Watchout you do not short anything!!!! There is mains voltage inside!!!
( edit) : for safety, It's better to put a plastic isolation sheet between the plate and the amp plate , leaving the electrical connection just on a small surface-
A clip holding the foil in place with some pressure where the foil electrically contacts the amp will be sufficient for this temporary test set-up.
Also the slits for ventilation on the amp plate are as many antenna's as you can dream of, so maybe if a) does not work try cover the whole thing. Be warned ventilation is going to be inexistant, so <watch any sign of overheathing, this is just a very temporary troubleshooting
Problem solved?
Then it's time to think of a more permanent functional ( safety/ventilation wise and aesthetics) solution
IF not,
Found this on a forum, a Behringer rep said :
“ RFI problems are always tricky to diagnose and cure. The first thing that I would try is to slightly move your speakers. Doing this will sometimes block the problem frequency and fix your problem. If that does not work I would try out a UPS (Uninterrupted power supply) and these can be purchased at your local computer store. The one you would want to look for would include an RFI filter. Proper grounding will help, also avoiding ground loops. Is there a computer monitor or other CRT-type device close by? If you turn it off, does the interference go away? Try a 2-prong to 3-prong adaptor briefly - does the RF go away? Sometimes it's carried by the ground lug. Try to eliminate any kind of ground loops by connecting your devices to one outlet.
We hope that we have been able to help you with this information. If the problem persists, feel free to contact us - we're here to help!
Best regards,
Your BEHRINGER Customer Support Team"
Try what they suggest . also You could start with ferrites right after the IEC inside the amp. I think it's not necessary to go and buy an ups just for a RFI filter, you could roll your own, provided you are a bit handy with soldering irons and oblige to safety ( especially while working with potentially lethal mains powered voltage).
PS: Also try to make a diy mains cable from Belden 19364. Earth the shielding of this cable on the wall socket side ( not the speakers side). If this does not help the FM, it will help boosting sound quality very effectively.
New developments
Yeah I contacted Behringer before and got the same reply. It's funny that they have a stock answer for a problem they don't acknowledge exists with their product.
I've got some new info about the speakers and I think I've solved the problem! First off they are not grounded at all. There's no 3rd prong on the power cable. I've had them plugged in for so long that I must of forgotten. And when I worked on the speakers I'd unplug it from the amp, not the power supply. So my faraday cage was not grounded either.
But the interesting development is that I recently moved the speakers to a friends house to see if the radio was a problem where he lived. They were quiet at his house. But when I got home I plugged them back in and... no radio!
This made me think that maybe the problem is that because the amp isn't grounded perhaps it's building up a charge somewhere that's somehow making something an antenna. That would explain why every time I'd change something about the speakers that required me to unplug them for a few minutes it would "fix" the problem. And then it would just come back. And when I grounded the tinfoil box to the amp plate I think I may of just discharged the amp plate to the tin foil. When I left the tinfoil box on it just built up a charge too and maybe that's why the radio got worse than it was before. I just built a bigger antenna. I can not back this theory up with any science. I just made it up.
But the good news is now it works! I just turn off the power supply when I'm done with the speakers and when I turn them back on there's no radio. This solution has worked for a few weeks now and there's no longer a tinfoil covered shoebox on the back of the amp. I'd be interested to know if this fix works for other people with the same problem. Or if anyone has a guess as to what's causing the problem in the first place. I'll post again if the radio comes back. But I think this may of done it!
Thanks again for everyone's help. You guys are teh roxzorz!
Mike
Yeah I contacted Behringer before and got the same reply. It's funny that they have a stock answer for a problem they don't acknowledge exists with their product.
I've got some new info about the speakers and I think I've solved the problem! First off they are not grounded at all. There's no 3rd prong on the power cable. I've had them plugged in for so long that I must of forgotten. And when I worked on the speakers I'd unplug it from the amp, not the power supply. So my faraday cage was not grounded either.
But the interesting development is that I recently moved the speakers to a friends house to see if the radio was a problem where he lived. They were quiet at his house. But when I got home I plugged them back in and... no radio!
This made me think that maybe the problem is that because the amp isn't grounded perhaps it's building up a charge somewhere that's somehow making something an antenna. That would explain why every time I'd change something about the speakers that required me to unplug them for a few minutes it would "fix" the problem. And then it would just come back. And when I grounded the tinfoil box to the amp plate I think I may of just discharged the amp plate to the tin foil. When I left the tinfoil box on it just built up a charge too and maybe that's why the radio got worse than it was before. I just built a bigger antenna. I can not back this theory up with any science. I just made it up.
But the good news is now it works! I just turn off the power supply when I'm done with the speakers and when I turn them back on there's no radio. This solution has worked for a few weeks now and there's no longer a tinfoil covered shoebox on the back of the amp. I'd be interested to know if this fix works for other people with the same problem. Or if anyone has a guess as to what's causing the problem in the first place. I'll post again if the radio comes back. But I think this may of done it!
Thanks again for everyone's help. You guys are teh roxzorz!
Mike
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