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A3 non-Bose - new head unit with buzzing noise!

Discussion in 'In-Car Entertainment' started by AndyJMX, Feb 15, 2010.

  1. AndyJMX
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    AndyJMX New Member

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    Hi all,

    New to the forums but in need of some advice! I recently bought a 2003 Audi A3 1.8T which came with the standard Concert CD player and non-Bose speakers etc. I got the head unit replaced through Halfords to a Sony one with bluetooth etc, but I get a buzzing noise, particularly through the rear speakers, and which raises and lowers in pitch with the accelerator. It is especially noticeable on low volume levels and is present whichever mode the head unit is on. I took it back to Halfords initially, and they tried different harnesses, head units etc but the buzzing noise was still there.

    I've seen some similar threads but they all seem to refer to the Bose system. Can anyone help me out? Much appreciated,

    Cheers,
    Andy
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  2. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    The buzzing is the puny rear amp. All non Bose Audi systems have the front speakers connected directly to the HU and the rears separately amped via a tiny amp located inside the tupperware subwoofer. This amp also "powers" the sub.
    Checkout which adapter the muppets at Halfords have used. It should be a PC9-404 which is the RCA input adapter like this:
    http://www.carstereos4u.co.uk/audi-...utoleads-pc9-404-harness-adaptor-819863--.php
    If they have stupidly charged you £40 for the speaker input adapter (PC9-401) then this is the source of the interference. Take it back and get the correct one. The 404 uses a very cheap hi-lo converter which takes the rear speaker output from the Sony and reduces it back down to pre-out level to feed to the rear amp. This adapter is prone to interference as it is a piece of garbage.
    If they have used the correct RCA adapter, it should be plugged into the rear RCA's on the Sony and rarely gives interference problems, but it's not unknown as the stock Audi wiring to the rear amp is poor, as is the amp itself. The amp is in an open frame with no shielding from electrical interference (alternator whine) and the low level rear pre-out signals are not shielded properly at the HU. I would rewire the rears directly to the HU and use the Halfords adapter purely for the sub (if it has a dedicated sub pre-out), as the Sony will have a far superior and more powerful internal amp than the Audi/Nokia garbage. If you don't want to do that then you could try attaching a decent earth lead from the chassis of the HU directly to the chassis of the car, behind the glovebox, keeping it as short as possible. If this does nothing then with the HU turned on and at zero volume and the engine running so you can hear the whine, try grouding this lead on different parts of the car chassis and see if you can find a spot that works. As a last resort you could buy a ground loop isolator from Maplins and connect this between the rear RCA's of the Sony and the adapter. Good luck, hope one of the above sorts it out.
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  3. AndyJMX
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    AndyJMX New Member

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    Thanks mate, that's really helpful! Might have to get my hands dirty and try a few options - nothing's ever simple is it? :) If not your explanation will come in handy if I have to explain the problem to a dedicated ICE shop which I think will be the next stop.
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