Stereo Interference.

[Skezza]

Hey,

I bought a new car stereo about 3 weeks ago and I'm getting a lot of interference on the AM band. 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 (was only available in UK). Great little car, similar to the Polo just smaller. The old radio was one of the 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 a head unit and 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 widdled down a lot of the 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 and it seems to pop at the rate of the tickover when stationary. 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 always returns. If I take my foot off the accelerator it always returns. This is very sort of, hit and miss. It isn't black and white 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 1 litre 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, if that helps. I also have a picture of the alternator if it comes to identifying the live/earth lol.

Any help would be brill //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Thanks //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

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[All_Logix 10+ year member]

Humm interesting issue. I am not familiar with this supressor, but from the way you described it, it sounds like a emf supressor? I would say that is going to just chill out any AC ripple from the alt, but your battery generally does a pretty good job of that. I would try getting one of those rubber antennas you can pick up, plug it in the back and just see if the issue is still there. I would also like to ask if it is possible that this vehicle had a power antenna?

 

[maylar 10+ year member]

You might be better off checking in with the VW forums, as it may be more vehicle than audio gear related.

AM radio interference can be a royal pain to trace. There are filters that you can put on the head unit power wires, and on the alternator (as you have). Most of the noise is radiated though, not conducted. Your ignition wires and spark plugs should be resistor types. As a last resort moving the antenna away from the engine can help a lot.

 

[Skezza]

When you say a power antenna? I know the OEM radio had like an antenna booster built in, because I had to buy a special adapter which kind of looks like a thin tube that I assume connects to ignition to boost the signal enough to pick up AM at all.

I haven't thought about trying a rubber antenna actually (i don't actually own one), what would doing this prove? Would it prove it's the aerial if the noise goes?

 

[Skezza]

You might be better off checking in with the VW forums, as it may be more vehicle than audio gear related.
AM radio interference can be a royal pain to trace. There are filters that you can put on the head unit power wires, and on the alternator (as you have). Most of the noise is radiated though, not conducted. Your ignition wires and spark plugs should be resistor types. As a last resort moving the antenna away from the engine can help a lot.

Yeah, I made a post at Club Lupo a week ago but I had a pretty limited response and I figured AM interference is a common issue.
When you say radiated, that means it's static right? (I'm a bit of a noob if you haven't figured out lol ) So it's not interference being transferred through wires, it's being picked up by components?

 

[Skezza]

Out of curiosity, would loctite on the thread of the external antenna make a difference?

I had a bee sting aerial stolen off my car once so I added a bit of loctite when I replaced it just to make it a bit harder.

 

[maylar 10+ year member]

Yeah, I made a post at Club Lupo a week ago but I had a pretty limited response and I figured AM interference is a common issue.
When you say radiated, that means it's static right? (I'm a bit of a noob if you haven't figured out lol ) So it's not interference being transferred through wires, it's being picked up by components?

Radiated means it's RF energy getting into your antenna. AM radio interference was the reason car makers went to carbon ignition wires and resistor spark plugs years ago. They keep the ignition sparks from radiating noise.

There is also noise that goes through the wiring, but most modern radios are pretty good at filtering that out.

Here are a couple of articles you should check out:

Car Radio Reception Article 2 of 2 - C. Crane Company (800) 522-8863

How to Remove Car Radio Static | eHow.com