Odd Amplifier/Radio Interference Problem

[normalicy]

OK, so I just purchased an Avionixx AXT 1200.2 (same as the Elemental Designs nine.1) amp off of ebay that "works perfectly". Of course, being the nosy person that I am, I opened it up before installation & was(n't) suprised to find that it had been repaired (rather extensively to me moderately trained eyes). This of course could be fine or it could be a bad omen.

Move on to today when I finally have a chance to hook it up & I play a CD. It sounds great to me. Then I switched on the radio.... nothing but white noise. I try almost every station & even the best sound like they are a point or two off from where they should be. So, I did a bit of trouble shooting & find that the upon unplugging the RCAs on the amp, the stations come completely back (amp is only hooked to the sub). My only current thought is that it's kicking some really nasty stuff back through the ground. Anyone experience this before?

[ppia600]

Where is the amp, is it in the trunk? I've heard of class "d" amps causing some interference with radio band, but if its that bad maybe the deck's antenna cable isn't shielded well near the amp. What kind of vehicle do you have it in?

[Eva]

I think that the amplifier was not repaired properly and as a result it's producing a significant RF potential between RCA ground and 12V ground. The cause could be be an insulation problem between supply transformer windings or between the power transistors and the heatsink.

[normalicy]

I had considered the amps proximity to the antenna as a factor & it is Class D (or Class T as they call it). The car is a Catera & the amp is in the trunk. However, the antenna is supposed to be built into the rear window, so I suppose that could be a factor. The antenna's insulation shouldn't have compromised, but I guess something might have happened. But nothing is visible.

I tend to believe your theory Eva, however, that sounds like quite a bit of work to fix. Is it not?

[ppia600]

If you have an aftermarket radio, try plugging a temporary antenna in behind the deck and route it to the front of the car to see if the noise changes. Otherwise it could be an rca problem like Eva mentioned. You could always try a ground loop isolator on the rca inputs of the amp as well.

[normalicy]

Actually, I was considering a ground loop isolator (haven't had the time with the holidays though). I'll probably try that first over the antenna thing, because pulling the radio out of this car is a pain.