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Aftermarket HU Problems

grumbas Nov 14, 2007

  1. grumbas

    grumbas Member

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    Hi, new to the forum having just got my first Audi!

    I'm looking at replacing the concert on my S3 as it's got a dodgy volume control.

    I've seen in various places that replacing with aftermarket units can cause the Bose setup to 'pop'.

    My question is, has anyone tried this with the new Alpine IDA-X001? As I understand it these pops are caused by the hu grounding the pre-outs to stop electrical noise being amplified. As this Alpine unit has no moving parts to generate noise, will the problem largely be eliminated?

    Thoughts please!

    Cheers
    Graham
     
  2. shufti

    shufti Member

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    i think most of the probs with bose speakers from an aftermarket head unit are caused because the bose speakers run at 2 ohm.... well they do in an a6 bose..... if they are 2 ohm in your a3 they will likely fry any head unit as i doubt that runs stable less than 4 ohm

    i'm replace the lot if i were you, the bose system is overated
     
  3. AndyMac

    AndyMac Moderator Staff Member Moderator

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    No you were right the first time, the popping is caused by the RCA's being grounded. This has nothing to do with moving parts.
    The speaker impedance is irrelevant as all the speakers run off the Bose amp which is 2 ohm stable.
    You will pretty much get the popping with an Alpine HU as it has high voltage pre-outs, unless you use the speaker input adapter, which will degrade the quality. Much better to upgrade the speakers and run them directly from the HU, with the sub running off the sub pre-outs on the Alpine. The sub will pop but very quietly.
     
  4. grumbas

    grumbas Member

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    Now I'm confused!

    The way I understood it was the RCAs only get grounded during electrically noisy activity, specifically power on/off and skipping tracks. With the latter I'd assumed this would be due to 'noise' from the motor on the cd mechanism?

    Surely the RCA's wouldn't be grounded the whole time, so with this particular Alpine unit which I'd expect not to generate any electrical noise, am I wrong in assume I'll only get the popping on power on/off.

    Andy, totally agree with you on replacing the speakers and re-cabling but at the moment I haven't got the time, money or inclination! Really looking for the best short term solution until the upgrade bug hits at a later date. I'm also guessing the 6" components about to come out of my Impreza wont fit the S3?

    Thanks for your help!
     
  5. dualmono21

    dualmono21 Well-Known Member VCDS Map User

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    im afraid you will get this phenomenon with pretty much any aftermarket headunit BUT its not the fault of the headunit unfortunatly its the amplifier which causes the problem (the headunit itself is actually silent as it uses something called a noise gate when skipping tracks or fast forwarding with the exception of pioneer head units whos units dont noise gate when fast forwarding )the only way to cure this is to change the amplifier or run off the head unit
    the former is a far more reliable and better sounding option
     
  6. grumbas

    grumbas Member

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    Thanks for the input, from what you're saying it only occurs when carrying out cd player related functions?

    So I guess you're confirming that as this particular Alpine unit doesn't have a cd player (ipod only) the problem shouldn't manifest itself in my desired setup?

    I agree a more comprehensive re-wire would give the best results, but I'm limited on time and want to get shot of my concert unit with its busted volume knob asap!!

    Thanks again!
     
  7. AndyMac

    AndyMac Moderator Staff Member Moderator

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    Grounding the pre-outs is just an industry wide design standard to avoid clicks & hiss when switching between anything on the HU. It is not just related to mechanical noise, and even if it was I doubt Alpine would redesign their pre-amp stage just for HU's with passive sources such as Radio/i-POD. As Dual has said already the problem is the Audi amp, not the aftermarket HU. Audi/Panasonic use such cheapshit components in the HU and such mickey mouse wiring that they needed to use a different method for reducing noise in the system. This involves a bizarre capacitor array on the input stage to the amp that filters noise. However as soon as you ground the input to this stage i.e. the RCA's then you discharge the capacitors very quickly which causes the pop.
    If you're just after a quick fix then buy a new Concert off ebay and hope it doesn't develop the inherrent volume problem, or alternatively wire in 2 capacitors on the RCA's to the rear amp which will delay the earthing effect. This has been well documented on here and seems to do the trick. A ground loop isolator on the RCA's may also work, but don't think anyone's tried this.
     
  8. grumbas

    grumbas Member

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    Well I splashed out on the new HU in the end, and just thought I'd post up the results...

    As already documented the capacitors in line worked a treat, but I remember why I don't like soldering now! Maplins didn't seem to have any 15uF caps as mentioned elsewhere on here but 22uF seem to do the job just fine.

    I also tried a ground loop isolator and this worked perfectly, but theres no way 2 of the ones Maplins sell are going to fit behind the HU with all the adapter harnesses etc.

    What I did notice with both setups though was a lot more 'noise' at low volume than with the standard concert HU. This might have something to do with the fact I was using the main battery feed to trigger the Bose amp whilst I was testing (see below).

    Now onto the next problem - the new Alpine HU is only pushing out 1.2v on the remote trigger and .25v on the power antenna - I think it'll be going back to the supplier on Monday!

    How easy or not is it to switch the Bose amp for another? Are all the necessary wires in place and its just a case of extending them to the new position? Just remembered I've got a 5ch Alpine amp in the loft that could be dusted down.
     
  9. AndyMac

    AndyMac Moderator Staff Member Moderator

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    As already said many times, with the Bose setup you really need to ditch all the Bose ****. A new amp will probably sound worse if it's left driving the Shitty Bose speakers.
     

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