Interference on rear speakers after fitting Sony head unit

Veedub68

Member
Good morning fellow A2 peeps. I have recently fitted a Sony head unit with steering column mounted remote, which is really useful. However there is interference from the rear speakers, only when the engine is running. It's very annoying as the rear offside tweeter is quite close to my ear, so for now I have disconnected the plug in the wiring adapter I bought, that serves the rear speakers. all works fine apart from this. Any advice would be appreciated, as I'm missing the surround effect of having the rear speakers. The adapter I have used is shown in the attached photo. I hope it's the correct one. My car doesn't have Bose.
 

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Sounds like a grounding loop to me - I'd google that for suggestions around how you'd tackle

Another long shot might be poor cable shielding especially if there has been cable splicing but grounding issue is more likely
 
Assuming it wasn't there with the OEM HU, then it's likely to be the adapter that's the root cause. The suspects are:
Switched 12 Volts from HU to rear amp,
Negative to rear amp
Line out, L & R (if both L & R rear speakers are affected, or whichever if just one side),
Screen on Line Out cable not grounded.
The low level of the audio signal from HU line out to amp input is very sensitive to interference. You need to look at the pin out for the Sony, and the Chorus/Concert (label on case), then sketch out the OEM pins, and their equivalent from the Sony. Once you have that in front of you, you can check that the adapter matches it. Logical approach will, usually win over guessing, but it's a bit long winded (who me?) Mac.
 
Assuming it wasn't there with the OEM HU, then it's likely to be the adapter that's the root cause. The suspects are:
Switched 12 Volts from HU to rear amp,
Negative to rear amp
Line out, L & R (if both L & R rear speakers are affected, or whichever if just one side),
Screen on Line Out cable not grounded.
The low level of the audio signal from HU line out to amp input is very sensitive to interference. You need to look at the pin out for the Sony, and the Chorus/Concert (label on case), then sketch out the OEM pins, and their equivalent from the Sony. Once you have that in front of you, you can check that the adapter matches it. Logical approach will, usually win over guessing, but it's a bit long winded (who me?) Mac.
I do like a good home-made diagram. What the hell, it's raining, so it'll give me something to do ?
 
One thing to bear in mind is that the front and rear speakers on an A2 use different amplifiers, the front are powered by the head unit, the rears from an amplifier under the driver's footwell.
 
I do have one blaupunkt amp from when i had bose fitted if needed (have all the stock speakers too to be fair). Though highly unlikely to have failed (never heard of any of these failing?).
 
One thing to bear in mind is that the front and rear speakers on an A2 use different amplifiers, the front are powered by the head unit, the rears from an amplifier under the driver's footwell.
That amp, for the rear drivers, is fed from the HU L & R line outputs. Hence pickup on those cables will give noise on the rears only.. Mac.
 
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