My son and I installed his new Sony CD player with a 120 watt amp, we are experiencing a alternator whine when the car is running. We used the RCA cables and installed a ground loop isolator on them and still have a little noise.
The only deviation from instructions is I used a ACC hot wire instead of a wire from Batt straight to the amp. This is in a 88 TBird with premium sound system. That is why I used that wire it was in the trunk feeding the old amp. Any help will be appreciated. Thanks.

Bill

Well I'm not sure what you mean by using an ACC hot wire instead of a wire from batt straight to amp... I'm guessing you are using the remote power (switched source to turn the amp on and off) to power the amp? If this is the case, it's not a good idea. I don't know what guage the wire is, but chances are it isn't big enough. For 120watt amp, small as it is, you should have about a 10ga wire, at least in my opinion. Go ahead and run a new wire all the way to the battery back to the + of the amp, and have it fused within 12" of the terminal. That may be part of your problem. Secondly, when you run a new power wire (please... I have seen too many hack installs), make sure to run it on the other side from the RCA cables. Running your power wire next to your RCA cables can cause noise. I generally run my RCA's down one side by themselves, and run my remote turn on and power wire down the other side. I have never needed a ground loop isolator and have never had any noise, and I have probably installed 50 stereos before. Also running a proper sized power wire will help minimize headlight dimming, probably not an issue for a 120 watt amp but an FYI.

Usually engine noise comes from a long ground wire and/or bad ground. Ground it as close as possible to the amp.

Like 72 said, You need a large hot wire going straight to the battery.

I agree to make sure the ground is CLEAN not on a painted surface and is the same size as the B+ lead. If the ground is on a painted surface sand the metal down to bare and resecure it..

The ignition is one of the dirtiest areas in an electrical system. If it were me I would run an 8 gauge fused wire directly from the battery. Use the same sized ground and keep it as short as possible.

I just did this exercise...and I chased my tail for weeks. Do what everyone says with the wiring (It sounds like you did and just ran the switched lead to ACC), but first disconnect the antenna lead with the motor running and see if the noise goes away. There are two ways noise can get into the system, via the power leads and via RF into the antenna. It's worth a quick check on the antenna to eliminate that as a source. I did and it solved my problem.

Chuck

Thanks for everyones great input. We will be trying those things tomorrow and I will post back how it turns out. Thanks again.

Bill

Didn't think about antenna but sounds logical.

Update, the problem was I was lazy and did not run a dedicated wire from the battery to the amp. that cut out about 80%. Installed a filter in the line and solved it 100%. Those fords have real noisey alternators