Hi,

I have an older mirage ps12-90 powered subwoofer. It worked great for years but now when you use rca line level inputs there is a humming sound. This does not happen when using speaker level inputs. I am wondering if it is the shielding around the input itself or maybe some sort of other internal problem that may not be as obvious. Regardless, I am hoping someone might be able to help me out with some troubleshooting or suggestions. Thank you

-rob

If you have cable TV, that is probably the problem. Insert a ground breaking device to where ever your cable television comes into your system. They make some costly ones, but a simple 1:1 ground isolator can be made by getting two 300:75 ohm balluns at radio shack and soldering the two 300 ohm ends together and inserting that assembly into your cable. Most likely it's a ground loop problem, and this should solve it.

Rob, Matt's idea could certainly be valid. Temporarily disconnect your cable TV cable. What he is suggesting looks something like this, if you use one of each type (one tubular, with wires and a female F-connector, and one rectangular, with screws and a male F-connector):



What has changed since the sub last worked with the line-level input? You might also try the substitution method; try another interconnect cable, or see (if the sub's power cord doesn't have a polarized plug) if flipping the plug helps.

Larry
www.fineelectricco.com







This message was edited by Larry Fine on 05/21/02 16:52.49.

Thanks guys, I will get back to you tomorrow after I get a chance to play around witrh it a little more. I appreciate the suggestions.

-rob

Did you ever figure out what it was?

Inquiring minds want to know!

Have you tried using a 3 prong -> 2 prong power adapter? This is probably the easiest thing that you can do (it worked for me!)

Besides being a fire hazard and against all electrical code...it works. ; )

I had a similar problem. After hunting for days, I found 1) a poorly shield cable going to the sub, and 2) an ungrounded cable line. After I fixed both, everything was quiet. That humming was driving me insane.

Merrill