Intermittent audio distortion (2004 VW Golf)

I have a 2004 VW Golf, with the original AM/FM/CD receiver replaced with a Kenwood receiver that has MP3 and Sirius radio capability.

In general, it works fine. However, there is an intermittent problem with distorted crackling in high frequencies on the left channel only.

I'm trying to locate the source of the problem so I can get it fixed (or fix it myself). I assume it could be any of the following:

==> an intermittent defect in the aftermarket receiver

==> a problem in the wiring harness

==> something in the power amplifier (still the original VW unit in the back of the car)

==> a defective connector plugging into the power amplifier

==> the left tweeter (front corner of the driver's-side door, near the side-view mirror)

or maybe something else entirely.

Any of these things are likely to be expensive to have an outsider troubleshoot. I went to the car stereo shop that installed the aftermarket receiver three years ago, and they said it would cost $$$ to tear things apart and find it (even if they ended up not being able to find the problem at all -- the problem is intermittent, and the guy I talked to wasn't able to hear the static even when it was happening -- probably messed up his hearing from listening to too much rock music cranked all the way up :-}). I'm sure the VW dealer would refuse to do a thing unless the Kenwood receiver were removed and the original radio put back in first -- and even then, it would probably be my luck to have the problem go away for a while, only to come back after they were done.

So . . . any ideas of how I can try to track down the problem myself?

At one time, I thought the problem might be with one of the two connectors that plug into the power amplifier behind a panel in the hatch space. If the static came, the next time I parked I would jiggle this connector -- or unplug it and put it back in -- and when I started up the car again, the static was gone, at least for a while. However, sometimes the static goes away on its own, even if I don't do anything at all. So maybe it's not the connector -- or, alternatively, maybe random vibrations are causing a connection to go flaky, and later be OK, and then later go flaky again . . . .

I should probably take a look at the tweeter and the wiring to the tweeter, but I'm not sure how to remove the black triangular grille over the tweeter without breaking something. Any suggestions from VW fans?

Rich Wales === Palo Alto, CA, USA === snipped-for-privacy@richw.org

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Reply to
Rich Wales
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Short and sweet, no.

As mentioned, intermittent problems are very difficult to find even for professionals with good equipment.

I think you are wasting your time, unless you really get lucky and find a bad connection, etc - and the odds of that being the problem are low.

Usually in cases like this you are better off to scrap the old radio and buy a new one.

But good luck, in case you care to try.

Reply to
HLS

Here is a general approach. Try unit isolation. This is basically trial and error instead of using special audio test equipment.

Does the Kenwood receiver have outputs capable of driving speakers? If yes, then bypass the power amp and just drive around listening to the Kenwood by itself for a while. If the distortion goes away, then it was related to the Kenwood or the wiring from the Kenwood to the power amp.

You can substitute an alternate device for every link in the chain: receiver, wiring to amp, amp, wiring to speakers, speakers. If you have the original VW radio, you could stick that back in and listen to that with the power amp for a while.

One other thing to check is whether you have a mismatch between the receiver and the power amp. Does the problem occur only when you have the volume cranked up? If yes, and the amp has a separate volume control, then turn the receiver volume down and the power amp volume up.

Check for good ground and power connections to the receiver and amp. A poor connection on any of these could result in the symptom you describe.

Best of luck, this isn't an easy one.

--Dave

Reply to
Dave Allured

=3D=3D=3D =A0 =A0 snipped-for-privacy@richw.orghttp://www.richw.org=A0 =3D=3D=3D =A0http:/=/en.wikipedia.org/wiki/User:Richwales If this was originally a Monsoon system, the problem may *be* the aftermarket head unit. I seem to recall that the "line level" inputs to the amp were lower level than standard, and a standard line level output may cause distortion. I also may be getting this confused with the older Aktiv systems so verify this before you run with it.

nate

Reply to
N8N

Switch the connections between left and right channels, e.g. feed the left channel of the receiver into the right channel of the amp. If the problem remains on the left channel then switch the outputs of the amp.

Reply to
Mike Walsh

The original sound system was, indeed, a Monsoon system. The power amp and speakers in the car are still the original equipment; only the receiver was replaced (with a Kenwood KDC-X679).

Indeed, the car stereo installer told me at the time that he was putting in some extra parts between the new receiver and the existing power amp to compensate for the nonstandard expectations of the Monsoon amp. I don't know exactly what they put in, but I imagine it may have been something as simple as a resistive voltage divider on each output. If this extra step had not been taken, I assume I would be getting nasty distortion all the time (not just sometimes), and on all four speaker outputs (not just front left).

I suppose it's conceivable that there could be something defective about the voltage divider circuit on the front left channel -- though I would tend to think that something like that would affect all sounds on the front left, whereas the problem appears to affect only the highs.

The idea of swapping left and right outputs and seeing if the static moves to the other side might be good, except that the audio output from this receiver is on an integrated wiring harness with a single multi-pin connector in the back of the receiver.

Rich Wales === Palo Alto, CA, USA === snipped-for-privacy@richw.org

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Reply to
Rich Wales

Ouch. I meant to type: "If the distortion goes away, then it was related to the POWER AMP or the wiring from the Kenwood to the power amp."

I like Mike's advice too, about switching right and left channels.

--Dave

Reply to
Dave Allured

Well, now, after pulling out my aftermarket radio and having a look at the installer's wiring job, I do know exactly what they put in to adapt the Kenwood radio to my Monsoon amplifier:

NOTHING. (!!!!)

The two wiring harnesses (Kenwood's own plug and its associated wires, and the back half of the original VW cable plugging into the back of the dashboard) simply have the corresponding wires spliced together, with no special gizmos of any sort in between.

My first thought went along the lines of "Yea, yea; Nay, nay" (Matthew 5:34-37) -- along with wondering if, perhaps, there might still be some basis to sue the installer for fraud, misrepresentation, etc., even though the installation job was done three years ago.

I was baffled, though, that the sound has GENERALLY been quite good (except for this intermittent crackling issue) -- whereas I had been given to understand that without any level adapters, the sound quality should have been horrid, throughout the entire system, all the time, all these years, because of the mismatched levels.

I wrote Crutchfield's tech support (I was, and still am, thinking of using them as a supplier for future upgrades) and asked them about the Monsoon level mismatch issue. For what it may or may not be worth, the two Crutchfield techs who corresponded with me on my question insisted that NO special adapter circuitry is necessary to interface my (2004 Golf) Monsoon amp with an aftermarket stereo -- that their own research suggested that recent-vintage Monsoon amps can be driven from speaker-level signals straight from a replacement stereo -- and that while older Monsoon amps did apparently require special adapter circuitry, this was NOT required in my case.

So maybe -- just maybe -- the installer did know what he was doing after all.

Interestingly, after I (carefully!) shoved the radio back into the car, the sound quality was fine and has continued to be fine -- no more static (at least, not yet; we'll see what it's like on my drive home from work today). If the static doesn't come back for some time, that MIGHT suggest a poor-quality crimping job in the wiring harness (on the wires carrying the front-left signal), and that my pulling the radio out and pushing it back in may have mechanically stabilized the wires in a "good" position for the time being.

Or, alternatively, there might be an intermittent problem in the level-sensing circuitry that (according to Crutchfield) allows my Monsoon amp to work OK with either low or high input levels. Or it could be in the stereo. If the problem persists, I may try recrimping the wire connections -- or, if I get really ambitious, try switching the front-left and front-right wires in the wiring harness and see if the scratchy sounds switch sides or not.

Rich Wales === Palo Alto, CA, USA === snipped-for-privacy@richw.org

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Reply to
Rich Wales

Not surprisingly, the static DID eventually return -- though, again, only intermittently.

And this brings up an intriguing (disturbing) possibility. It's quite possible, I imagine, that a design flaw in this level-sensing circuit might have gone unnoticed by the Monsoon system designers, since the flaw would never show up in normal operation as part of a factory-original Monsoon installation.

And, if this is the case, my VW dealer could most likely never be convinced to acknowledge the problem or replace the amplifier under warranty -- since if (as they surely would demand) I were to reinstall the original radio before they would even begin to investigate the problem, the circuit in question would not be exercised and everything would work fine -- thus "proving" that the problem was in the aftermarket radio and not in the amp!!

The most likely possibilities now seem to be the following:

(1) A problem in my Kenwood KDC-X679 receiver -- can probably be ruled out by swapping front-left and front-right outputs from the receiver and seeing if the static moves or stays put, though this would require resplicing in the wiring harness.

(2) A problem in my factory-original Monsoon amplifier -- may be difficult or impossible to diagnose, but might be possible to bypass by installing the level-adjusting circuitry that the stereo installer "should" have included in the wiring harness in the first place but didn't.

(3) Any of various wiring problems, including poor crimping, bad connectors, or speaker issues.

Assuming I want to pursue this myself (since I'm unlikely to get anyone else to pursue it for me without it costing an arm and a leg), EXACTLY what sort of "level-adjusting" module or custom circuit would I need to use in order to adapt the speaker-level outputs from my aftermarket radio to drive my Monsoon amplifier as originally conceived (bypassing the alleged adaptive level sensing that's supposed to make adjusting the level unnecessary)?

Rich Wales === Palo Alto, CA, USA === snipped-for-privacy@richw.org

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Reply to
Rich Wales

(3) Any of various wiring problems, including poor crimping, bad connectors, or speaker issues.

This is were I would start. Make sure all connections are clean and tight and eliminate all the poor crimps by soldering and shrink wrapping. Only then can you procede in your troubleshooting, if that does not take care of the problem. I would also double check all grounds in your audio system as well.

Reply to
Mike

I *may* finally have managed to pinpoint the cause of the intermittent static in the front left tweeter of my 2004 VW Golf (with aftermarket Kenwood receiver and stock Monsoon amplifier and speakers).

Over the weekend, I put a few layers of electrical tape on either side of the big plug that (I believe) is what carries audio signals to and from the amplifier -- and then I pushed the plug in firmly, all the way, so it's held in place not only by the clips on the long sides (where I naturally didn't put electrical tape), but also by the extra bulk of the (slightly squishy) tape.

The static problem appears to have basically disappeared. There may have been a couple spurts of brief static, which went away on their own, but for the most part, I'm hearing great sound now (including clean highs out of that tweeter).

So it looks (or, shall I say, sounds?) like the main cause of the static problem was an intermittently bad contact in the connection to the amplifier. Presumably, the vibrations of driving would cause the plug to jiggle slightly, resulting in a bad connection (most likely in the wiring going to the front left tweeter, since no other speaker was ever affected). Sometimes, more vibration would make the connection become "good" again -- making the issue that much harder to track down.

The plug was snapped "properly" into place, as far as I can tell, so the bad contact must presumably be something very subtle.

Two questions.

First, does this sound reasonable? Does this sort of thing happen in real life? :-}

And second, is there a more "proper" way to fix a problem like this, or is padding the plug with electrical tape for a tight fit as good a solution as anything else?

Rich Wales === Palo Alto, CA, USA === snipped-for-privacy@richw.org

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Reply to
Rich Wales

Sounds entirely reasonable. It's possible there's just oxidation and/or corrosion on the contacts, especially if you live near an ocean (salty air).

What you can try doing to cleaning the contacts both on the plug and on the amp - use some contact cleaner or isopropyl alcohol (the higher percentage, the better). Then when it's dry, apply a little light grease to the contacts before reconnecting them, ideally something sold for battery terminals for exactly the same purpose: preventing further oxidation/corrosion.

Reply to
Matt Ion

Rich,

It may be that you need to get a line output converter (LOC). These are designed to convert the signal level of high level speaker outputs to low level voltages (usually 4V + or minus). As I recall, the OEM Monsoon amps do not have low level interconnects so you will have a mismatched output level that will either over or underdrive your head unit and cause the distortion you describe. Some of the better modules are adjustable for tuning to different head units. You may want to do a search for a 'PAC' unit or look at Crutchfield. Do you know if your installer kept the Monsoon amplifier wired up or if he's simply using the amp in the head unit?

Good luck. If you need more help, get in touch. Andrew.

See if this helps:

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Reply to
AWN

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