Grounding?

[04X3]

I have a USAspec pa12 that I just got installed. Lately, I've noticed a high pitch whine, specifically at higher volumes. It's not unbearable, and if I turn the volume down I can't hear it. Is this a grounding issue? If so, where? In the trunk area or in the center console where the PA12 unit is?

[big bob]

You have a voltage differential between either the amp or radio and the USASpec. Move the ground of the USASpec to either the radio or the amp to test if the problem goes away. It's most likely at the radio, since the amp is AC coupled.

[04X3]

Thanks for the reply big bob,

Where is this ground located and what color is the wire? Do I have to rip apart the dash to do it? I heard common grounds were not a good idea, but I will try this as soon as I know how to lol

Thanks for the help

[big bob]

I'm sorry, I know noting about the USASpec or the way it is installed in your car, since it is not available in the UK. On BMWs GND is brown.

[04X3]

Bob,
thanks for all your help. I tried moving the wires a bit today, and that helped. Unfortunately, the iPod cable got a little smooshed and the wire almost got cut (I nicked it a bit) and after a little while I heard cell phone interference. I moved the wire back to original position with the magnet on the bottom of the cable close to the unit, and the sound seems to have improved (can't hear the whine anymore). If it acts up again, I guess I'll just buy a new cable and try my luck. I don't think it is a grounding problem now as moving the magnet seems to affect the noise and this setup seems to have fixed the problem for the time being.

[big bob]

Good stuff, thanks for the update.

[04X3]

Problem still exists. The cable is definitely nicked and the noise started when I tried to route an aux cable with with ipod cable through the same, small hole in the center console. Must have nicked the cable then
Anyways, I've bought another cable but if that doesn't work then back to the shop it is.

[big bob]

Damage to the shielded cable could easily cause the effects you are describing.

[04X3]

Alright, I installed the new one and the noise is considerably better. However, when the volume is full or when it is close to full, I can hear a quiet hiss from the unit (sometimes when I change songs I hear a tick as the unit is working). Is this normal? I can't really remember from before... I think my cable from the USAspec to the radio is fine, don't think I nicked that one while moving wires...but that's not even shielded is it?

However, I can only hear the hiss on very few songs and when in the middle of a song with a pause of silence while the volume is high. Am I good or am I getting excessive feedback from the unit?

All in all though, I'm satisfied.

[big bob]

Poor SNR (hiss) could be a number of things, not limited to the fundamental SNR of the MP3 file and player, the SNR of the USASpec and the USASpec gain setting that defines the SNR between the USAspec and the radio.