2nd Gen Non-Engine/Transmission Noisy XM radio - Truck power issues

[BroncoMarc]

I seem to have some noise issues in my truck's electrical system. I just got an XM radio and I plugged it into the front input of my Aiwa radio. I've also used this input with my battery operated MP3 player.



With the XM radio I get a ton of noise. I get a whine with the truck not running, and the XM raidio not even turned on. It's a little worse with the XM turned on, and a lot worse with the truck running. Every little thing changes the noise. . engine RPM, hitting the brakes, etc...



I've narrowed it down to my truck's electrical system. I tested the XM in another vehicle and it sounded fine. I tried running the power to another vehicle and plugged it into my truck's radio and it sounded fine. This also make sense since my battery operated MP3 player sounds good.



What could cause noisy power?

 

[BTowler]

Bad ground, check the connections.

 

[BroncoMarc]

I just tried running a 'supplement' ground from the battery to the outer part of the power port. . It didn't help. Both power ports do the same thing.

 

[EricBu12]

Then you need to get a RF noise filter for the power side of the unit. Your local radio shack or equiv. will have it.

 

[DF5152]

something else is going on u should have no noise if the truck is not running?

 

[BTowler]

Originally posted by DF5152

something else is going on u should have no noise if the truck is not running?

Thats why my first thought was a ground problem or ground loop.

 

[tp0d]

Yea, you should have completely clean power from the truck side with the engine off. The alternator is the only source of AC hum. Did you try putting the ignition in the 'accessory' position? I think this just turns on the radio without the PCM, etc.



My guess is your XM doesnt like your radio w/ the same ground. I have also seen some crappy front inputs, I cant vouch for the quality of them. Best thing I could recommend is to buy a 20-30$ FM modulator for the XM, the FM radio side response will usually be MUCH better than any kind of aux input the radio has built in. Probably give you some better low level gain as well. And it can eliminate the ground loop between the radio and the XM, being that an 1/8" jack has a solid ground on it. The radio shack power isolation xformers work well, you could also try a 50,000uf 30vdc capacitor in series with the positive feed.



good luck



-j

 

[BTowler]

I have to disagree with jkomaromi's post, line input will give you better frequency response than an fm signal, it would be better to have rca inputs than a 1/8" jack, but line level has a greater dynamic range than an fm signal does. If you have hum with the engine off and the key in the accessory position, it is a ground loop problem and will be difficult to correct since there is no metal chassis on the xm to connect to the radio chassis. This is where he is right that the best way to eliminate the hum will be the fm modulator.

 

[tp0d]

Well, I just go from personal experience from some of my installs. The 1/8" jack is a bother, unplugging and replugging wears the contacts (allowing for less response and more static), and I've seen a few the victim of a hard bump, and shear off part of the face of the unit and/or the plug. As for the frequency response, FM is typically 30-15k, human ears cant distinguish anything at or past those limits, so its a moot point...



-j

 

[BroncoMarc]

What exactly is a ground loop?



The front 1/8" input works great for my MP3 player, but that's battery operated which is why I'm suspecting something weird with the power going to the power outlet.



I just thought of something else my truck was doing a while back. I started to do a torque converter lock-up switch, but when I put the jumper in to replace the relay it made my alternator whine when the key is on. Could this be related?

 

[BTowler]

I don't know exactly how to explain what is going on, but I should actually say that you need a ground loop. A ground loop is when you connect the chassis of your audio equipment with a wire that allows them to share a better common ground. As far as the alternator whining, I've never heard of the alternator itself whining unless a bearing is going out.



jkomaromi, the upper limit of human hearing is in the 18k to 20k range on average, unless you have hearing problems. You are right about mechanical wear on the jack, which is why I stated rca inputs are the better choice.

 

[DF5152]

where r u drawing power for the XM unit

 

[BroncoMarc]

I've tried both power outlets (Cig. lighters)

 

[GMincher]

PEOPLE!!!! Those who drive Cummins don't need all this radio nonsense!!!! You have beautiful music as long as you're in motion! Now if you drive some lil' front drive 4 cyl. , THEN you need a system!! I'm messing with you... but I'm serious at the same time.

 

[datablitz]

i had the same problem, solved it with a ground wire from the metal frame of the radio (the am/fm deck) to the body... . solved my hum

 

[BroncoMarc]

Just went out and tried that. . I ran a wire from the metal cassis the radio slides into (all I could get to without taking the radio out) to the ground of the same cig lighter the XM power is plugged into. It didn't change the hum/whine at all, but it produced static when I moved the wire around.



I also tried running the power cord directly to the battery (tip of the plug to the + and a wire from the plug to the -). . Got the same results.

 

[BroncoMarc]

I'm almost convinced it's a ground loop problem. . I got a wireless FM modulator today and it works great with it. Not quite the quality of a direct connection, but no whine!



I'm going to look for a ground loop isolator so I can use my direct connection. . Hopefully that will fix it.

 

[tp0d]

Good to hear it mreiter... . Depending on the quality of the modulator, that will affect output quality. Easier overall IMHO... Anyways, Radio Shak sells an RCA ground loop isolator (all it is, is a small transformer sandwiched between two stereo RCA connections. ) The ground loop you hear is DC being introduced into the AC input stream, and the transformer will not pass DC. I believe they're less than $10. The connection issue is there tho, but you can probably get some rca-1/8" adapters there too... . Just watch prices, Radio $hak can beat ya over the head sometimes. .



good luck



-j

 

[BroncoMarc]

FIXED ! ! !



Finally went out today and got a Rat Shack ground loop isolator. It's clear as a bell now!



The modulator was acceptable, but there was a little bit of staic since none of the frequencies the modulator used were completely clear here in Cincy.





Thanks for all the suggestions!



- Marc