DI box

[Tabitha]

Has anyone needed to install a DI box to reduce hum in speakers? If so how the heck to they connect........ HELP!!!!!

[GPW]

Tab' , being a musician , a DI box is usually used to pick off a line level signal from a speaker output ....Not to reduce Hum ...  Unless you have something different . Hum is usually the result of a faulty power supply ... What are you using that makes Hum ?

[noseoil]

Is it a regular automotive CD/radio deck with the hum from the speakers? Is it there all the time, or is there some other electrical item on your system which makes this hum? Is it a "60 cycle" hum? The inverter comes to mind as was already mentioned, but other electrical appliances can contribute to it if they're on at the same time.

[pchast]

I seem to remember Auto stores used to sell a capacitor/coil pair that could be used to
clean up the power to the radio.... before spark plug wires went all to carbon instead of copper.

[Tabitha]

We run an XM radio hooked into a 12 volt amp with speakers. We didn't have the hum until I added the last few usb ports in the cabin now I have a hum.

[GPW]

Maybe it’s your wiring? Try disconnecting the new USB ports (temporarily) Sounds like your wiring is making a “ground loop” ...

[noseoil]

Tabitha, I appreciate your post on this problem. The USB ports I've added will be switched, hopefully it will help to isolate the problem in the future. If it turns out to be the USB's which are causing the problem, you might consider the use of a switch to keep them cold, unless they're actually in charging mode with something plugged in. Here's what I did, because I didn't want to have the blue LED's on all the time while sleeping.

I'm wondering if I will have the same issue with my CD deck, once I finally get to that point in the build. Hmmm........

[Greg M]

A lot of USB converters will cause hum like that. It's the switching power supply that's built into them. A power line filter on the car stereo's 12 volt lines will probably clean it up.

[Greg M]

Something like this: http://www.parts-express.com/pyramid-ns ... r--265-047

[Shadow Catcher]

We have an XM receiver that is fed through a car stereo. I have one automotive style power point and a Belkin USB adapter which can power/charge the cell phones or iPad. Normally when we are on 120AC we just use the wall warts there are four 120 outlets at the head of the bed.

[Tabitha]

Thank you everyone I'm thinking it is a ground loop that's why I had questions about the DI box.

Thank you Greg I think I'm going to try the box you recommended, I'll keep you posted.