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AM Interference - Alternator? Ignition?


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Skezza
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May 24, 2012, 5:47 AM

Post #1 of 4 (1171 views)
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AM Interference - Alternator? Ignition? Sign In

Hello everyone,

I wish I'd known this forum existed a week or so ago. I've been fumbling around trying to fix my radio.

Don't be fooled by anything I write, I know literally next to nothing about car stereos. I'm a software engineer by profession, so unless there's an app for that I'm pretty much screwed lol! Please look past my noviceness :P

I bought a new car stereo about 3 weeks ago. It isn't a Pioneer or an Alpine. So, I guess it could be simply not a very good head unit and yes, I'm keeping an open mind.

A little background, the car is a W reg (2000) VW Lupo. Great little car. The old radio was one of those VW BETA's. Tape deck, 7 watt output, Not great quality audio (mushy), although seemingly a reasonable internal antenna (and suppressor?). I decided not to go for the OEM CD Player replacement for a number of reasons and opted for an aftermarket stereo with Bluetooth, USB, etc etc etc.

To put it simply. My car speaker & audio setup is VERY simple. In fact, taking the radio out altogether is the only thing that could make it simpler. I have 2 speakers... passenger door, driver door. That is it. No sub, no parcel shelf speakers, no rear fitted speakers. So the interference ISN'T coming from RCA cables or amplifiers or whatever.

I've slowly and surely widdled down the initial issues and now I'm down to just the AM Interference. Unfortunately, I actually listen to a lot of AM radio because almost all sports is broadcast over AM, so it's a bit of a pain not being able to hear it as a clear as my old OEM stereo, which, while the audio quality was lower, had a lot less interference. The interference on the AM just a few days ago was unbearable so I'm actually in a better position than I was when I started but I feel like I'm so close to having eliminated almost all of it.

The interference is a crackle, like popcorn popping. It isn't there when the engine is off. It DOESN'T whine, but it does get louder as I drive faster. Here's the catch. Sometimes... in fact, a lot of the time, when I hit 3k revs it goes. It literally disappears, then as I get faster and pass sort of 3.5k revs it sometimes returns but as soon as I get slower, it almost always returns. If I take my foot off the accelerator it always returns. This is very sort of, hit and miss. It isn't definitive which is why I genuinely am stumped by this. There isn't that much else I can tell you. If I could just eliminate this, then the stereo is a real hit and to be fair, since it's just a crackle now, rather than the complete mush (was like complete TV static) that was a week ago, I can probably live with it, but I'd love to get rid of it.

I was recommended an alternator interference suppressor by some kid in a shop who was clearly more interested in talking to his mate about getting +1 BHP out of a 1l Fiesta. I got one the other day which is essentially a 3 micro-farad capacitor that clamps on the alternator.

I haven't fitted this yet as I was hoping some of you could guide me in any other direction that might help before I do. I can see this being a real pain as none of the wires going into my alternator seem to be colour coded. Multimeter it is.

I have a video which I'll see if I can upload to youtube in the next hour or so, it does demonstrate the 3k rev thing.

Thanks :D


Discretesignals
Veteran / Moderator
Discretesignals profile image

May 24, 2012, 4:08 PM

Post #2 of 4 (1086 views)
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Re: AM Interference - Alternator? Ignition? [In reply to] Sign In

We don't have the vehicle here in the states, but if the noise in the AM band occurs with the engine running and sounds like popping or crackling noise, you could be picking up ignition noise. Inspect your plug wires if you have them and make sure they aren't flash burnt or leaking. There are so many solenoids and electrical components it's hard to determine what is causing the noise on your radio. It is also important to make sure that all your ground connections in the engine bay are clean and tight.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Skezza
New User

May 25, 2012, 4:03 AM

Post #3 of 4 (1056 views)
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Re: AM Interference - Alternator? Ignition? [In reply to] Sign In


In Reply To
We don't have the vehicle here in the states, but if the noise in the AM band occurs with the engine running and sounds like popping or crackling noise, you could be picking up ignition noise. Inspect your plug wires if you have them and make sure they aren't flash burnt or leaking. There are so many solenoids and electrical components it's hard to determine what is causing the noise on your radio. It is also important to make sure that all your ground connections in the engine bay are clean and tight.


Thanks for your reply. Mechanically, the vehicle is similar to a Polo from 1998-2005 which I guess you do have in the states right? The main differences of course were size, chassis and of course, price.

That sounds rather beastly Laugh so I might have a friend of mine go over that.

So you don't believe it's caused by the alternator? I've got an alternator suppressor here but wasn't sure if I should fit it. perhaps I'll fit it, see if it makes any noticeable difference, then decide how to proceed lol.

Thanks :D


Discretesignals
Veteran / Moderator
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May 25, 2012, 8:28 PM

Post #4 of 4 (1023 views)
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Re: AM Interference - Alternator? Ignition? [In reply to] Sign In

We don't have the Polo here in the states either. Usually an alternator will make a whining noise instead of popping. If you think the alternator may be generating RFI that your picking up on the AM band, unplug the electrical connector from the alternator. This will shut the alternator off. With the alternator turned off and engine running, see if your noise disappears.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on May 25, 2012, 8:28 PM)




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