I had an amp installed last week by a terrible place in berkeley(Best Auto Stereo) and to fix the alternator whine they put two noise filters inbetween the RCA's and the amp. I've heard about noise filters in passing, but never needed them before. (Seeing as they were replacing the exact same amp, i'm suspect about actualy needing them). I've got a few quiestions...

1) Do they lower sound quality? I go by the theory that anything in between the head unit and the amp must be bad, but I've been wrong before.

2) Because they're lazy and didn't open up the dash, they put them on backwards according to the markings. What's the the difference? I assume i'll just reverse them myself when i get some time....

Matthew

Noise filters don't pass low frequencies very well - you *will* notice this if you have a sub...

Hugo

Do they lower sound quality?

Supposedly, they work by converting the signal into optical, breaking the electrical connection. Dunno exactly how they pull it off, but as Hugo said, they don't necessarily have the full range of frequencies and you might lose some of the extremely low frequencies. Like Hugo said, I wouldn't worry too much about it if you don't have a subwoofer. Most regular car speakers can't reproduce those low frequencies so you won't miss them.

Someone once posted a description of the frequency response of a certain brand of opto-isolator, and it sounded pretty good. The one by Radio Shack, however, doesn't pass the low frequencies well. Anyone have a link to the good one so that I can put it in the FAQ?

they put them on backwards according to the markings. What's the the difference?

They are just two independent line-level channels. So if they made them backwards like this:

Empeg Left ---> Isolator Right In--->Isolator Right Out---> Amp Left
Empeg Right ---> Isolator Left In--->Isolator Left Out---> Amp Right

Then it makes no difference at all.

How to check: Move the balance and fader controls on the empeg and listen to make sure they go in the correct directions for all four channels.

Finally, understand that ground loops can (with some care and time) be solved without using the isolators. An isolator is just an easy/quick fix. Please click here.

Thanks tony. Yeah, I plan to redo just about everything this summer and hope that the ground loops disapear.

The inputs are backwards in the sense that they have an amp side and a stereo side, and mine are reveresed. Everything seemed to work fine untill this morning, when I got in the car and the empeg started up, started playing music and shut down the display. After the third pullout-putin, it worked normally. Is this a known bug? I havn't seen anything about it, so it could be related to having the wrong amount of resistance on the RCAs? The dash is still half-open, so I'll either return the noise filters or move them to the empeg side of things.

Matthew