Perhaps someone can explain this?
I have a 98 Audi A6 2.5 TDi and have just replaced the original Audi Concert System head unit with a Sony CD player head-unit.
The new Sony unit creates a background buzz in the back-left speakers, which appears to be vehicle speed related (i.e. you can hear it increase in frequency with speed and it is silent when the car is stationary!). The engine speed does not affect it.
The shop that fitted the unit have tried at least 4 different head units in place of the Sony one and they all see to buzz in the one speaker. They have also tried fitting a suppressor on the mains line, which made no difference.
The original Audi unit didn't do this, so I am puzzled as to why non-Audi kit does it.
Any thoughts as to what I am missing!?
Dave
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Suggest that the speaker wire is picking up interference, but from where is a mystery. Also why then would the original radio unit not have the interference? Have you re-fitted it and if so, is it still interference-free, or did something get disturbed when you removed it?
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Ok its interference.
There are two types
There is electrical interference that rises in pitch or loudness or frequency with engine revs. So rev the engine to see if its that.
Cure is to earth the radio head body, the autochanger body, screen the autochanger connection cable, put chokes into power feed to autochanger and radio etc etc. Any car audio shop can diagnose and fix this.
And there is speed interference - caused by static from tyres and wheels. Only heard when moving - rises in frequency/pitch/loudness with speed - not engine revs. Sounds like yours. This is not common and will mystify a lot of car radio bods.
The only cure is to earth strap the suspension components on the side affected, or change the tyres or check and change the brake pads (if they rub they can generate static). You could try screening* the speaker wires on the side affected - this would help to cure it and also if it was picking up abs/traction control pulses
*you would have to buy screened twin core cable, and relay speaker wires from audio output to speaker.
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Does it do it in wet weather too?
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I would assume you mean by head unit a pre amp using seperate power amp.if so a connection to power amp from head may not be connected properly ie the power amp/speakers aren`t getting full signal.could be wrong?
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The quality of the radio earth can also have an effect. Complete radios nearly all have a bolt on the back of the case which should be attached by a heavy bit of cable or braid to a part of the cars structure.
I've never dealt with split units, but I would imagine a similar treatment of each unit to be a good idea if possible.
The reason for this is internal eath connections are often too poor to be effective and the case instead of functioning as a sheild, is being an aerial.
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Thanks for the varied responses.
To be clear, ONLY the actual head unit has been changed from the original factory fitted Audi Concert tape/tuner to a Sony CD/MP3/Tuner. No other modifications have been made to the wiring, speakers or amplification.
The buzzing is definitely SPEED related. It is completely silent when stationary & ticking over, but becomes faster and louder as the car builds up speed.
I asked the fitting dealer (Halfords) for a refund as we were clearly reaching the limits of their knowledge. Unfortunately, I was a little too prompt in selling the old Audi head unit on Ebay and now have a car with no stereo!
I will take the car to a specialist car-audio place and get them to fit the unit and pre-warn them of the problems. I take on board the suggestion to replace the cabling with shielded cables to the speaker affected. Presumably 'shielded' just means tightly twisted pair cabling?
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>Presumably 'shielded' just means tightly twisted pair cabling?
No it means twin core cable with an outer sheath of braid or foil covering the two inner cores. The braid or foil can be earthed (at one end only to prevent a earth loop and causing a hum)
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dave, i also have an A6 with a concert stereo. i always thought they were quite good units, how come you changed it?
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DBA,
I changed the Audi unit because
a) it was developing a fault with the volume knob, where it would jump to full-volume or complete silence when trying to adjust the volume. From searching the Internet, it would appear this fault is pretty common on Audi units of the same age.
b) it was a tape desk - I have no tapes anymore.
c) I wanted to fit a unit that could play MP3 files - the sheer number of MP3 files on one CD means that you don't need to fit a disc-changer.
Dave
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Dave,
Did you ever get to the bottom of the buzzing problem? I've got the same on my A3 having recently installed a new Sony head unit. However I get the buzz when the ignition is on full or the car is started.
I agree it's very frustrating as the original Concert unit doesn't do it.
I've read that it may be something to do with the gains to the amp powering the rear speakers, hence hearing it one side (the standard amp is situated in the left hand side of the boot). But I don't really understand what "gain" is.
Let me know if you solved it.
Cheers
Dan
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Dan
Don't overlook the fact that most VAG audio units have a speed-sensor feed [usually from the ABS ECU] and a built-in diagnostic circuit [K-line, or now CAN-HI/LO] hard-wired in their ISO plugs.
If these two systems aren't properly disabled, they can show all sorts of weird effects on non-standard units and may even cause multiple ECU [and scanner] damage.
Keep any head-unit removal keys handy; as you may need them if you ever suffer a problem requiring a scanner to be connected. Most clued-up places won't even connect their expensive scan-tools to any VAG [or GM] car with a non-factory unit still wired-in.
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My Son informs me that this is a common problem and the Bose Amp in the rear N/S has to be disconnected and bypassed so the Sony drives the rear speaker directly. Check what subwoofers are fitted as some are driven from the bose amp and will require the amp to drive them. Regards Peter
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Screwloose,
Thanks for the advice, what do you mean by "properly disable"?
I'm quite sure that you're on the right tracks as the buzz comes in when the ignition is on and therefore when something is being activated.
I tried to get near the speaker this weekend to check connections etc but this proved to be more than a simple task.
BTW the ABS light came on for a little while today, could this all relate?
Regards
Dan
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Dan
"Disable" as in - disconnect that unit and urgently consult an audio specialist.
I've just had a look at an A3 ABS ECU's wiring diagram and it's all part of a fully-networked CAN-BUS system.
There's a good chance that the factory radio was an essential node in that network, so it's distinctly possible that other systems are reacting to it's replacement.
Sadly; with these networked cars, making changes to anything is like walking in a minefield.
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Dan,
I also have an A3 (non Bose). Retaining the original headunit, I have installed an Ipod using the dension icelink cable. As soon as the ipod is selected I get interference (even without the ipod attached). The noise does get worse as the ignition is swtiched on and reving of the engine occurs.
I bought a Ground Loop suppressor today from the local Halfords, but it is only for units upto 5amps...the Audi concert runs a 7.5, so I refunded it and I'm looking at getting a better unit.
Have you had any success in solving your interference?
Cheers :)
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