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Help with correct lead for replacing rear amp only

Discussion in 'In-Car Entertainment' started by StuBill, May 30, 2013.

  1. StuBill
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    StuBill New Member

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    [May 30, 2013]
    I'm working on a modest upgrade to the stock system in my 2010 A4, but despite loads of great reading here I am still a bit confused with leads.
    I have replaced the tupperware sub on the rear shelf with a JL 10", and now am looking to replace the amp in the rear cubby hole in the boot. I'm not planning to replace the HU (concert non bose). Is there a lead that jsut converts the current plug into the rear stock amp to allow wiring to an aftermarket amp fitted in the same place without hacking the original wiring to bits ?
    I believe I would still need power feed for the upgraded amp, but that's no bother as the battery is in the boot.
    Many thanks.
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  3. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [May 30, 2013]
    No there is no OTS adapter, just strip the end off an RCA lead and solder small blade terminals to the left, right, screen and remote and then plug these into the Audi plug. Avoids hacking the stock wiring.
    You will need a 4channel amp if you want to keep the rears
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  4. StuBill
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    StuBill New Member

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    [May 30, 2013]
    Cheers Andy, that's a fine solution.
    Sorry if I am being dim though, if I use the L/R pre outs for amp channel 1/2 on the rears, do I split it to feed channel 3/4 for the sub, or bridge the amp output to all 3 speakers ? Thanks again, I am sure this is basic stuff, lol.
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  5. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [May 30, 2013]
    On most 4 ch amps you can set the input mode so that the ch 1 & 2 input also feed ch 3 & 4, if not then just use Y splitters
    If you have an aftermarket HU then you can simply rewire the rears to the HU and use a 2ch or mono amp just for the sub
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  6. StuBill
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    StuBill New Member

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    [May 31, 2013]
    Got it, thanks again Andy. That gives me some options on the wiring.
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  7. StuBill
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    StuBill New Member

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    [Jun 1, 2013]
    In case anyone is interested, after a little fishing around the rear amp, the mating connector half (amp side) of the rear loom is a Tyco connector, part number 1534046-1, stocked by Farnell : 1863527.
    I have a couple on the way :)
    I may either make up an interface loom wiring off the PCB pins of one of the connectors, or even look at designing a small interface PCB + enclosure with RCA's and a 12V remote connection (I design PCB for a living which makes it much easier :)) .

    Edit : could even do the speaker feeds back through it too....would be very neat !
    Last edited: Jun 1, 2013
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  8. StuBill
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    StuBill New Member

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    [Jul 1, 2013]
    OK, I now have the OEM 32pin connector (not easy to get hold of but managed it:whistle2:) and a new 4 channel amp, but have quickly hit the first hurdle. It appears the front speakers are driven or at least 'routed' through the amp in the boot also on the B8. Seems a strange way to do things. I assumed the fronts were driven off the head unit ? Does this mean to cover front, rears and sub I need a 5 channel amp (or a 4 and a mono) ? Or is there another way that I am missing. The new amp has speaker level inputs (and converter) so I suppose I could do it that way for the rears and sub, although I would rather do it at line level. Any thoughts ?
    Thanks very much.
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  9. StuBill
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    StuBill New Member

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    [Jul 4, 2013]
    I don't suppose anyone has a link or diagram for the pin out of the 32way connector that goes into the rear amp on a B8 (non B&O) ? I have found a diagram by trawling the web, but it is incorrect for this model (wires not in positions as shown). It's driving me nuts. The connector is split into 2 portions, a group of 22pins and a group of 10pins. All thin wires into the 10pin portion (guessing pre outs, microphone etc.) and thicker gauge wires into the 22pin portion (speakers and power).
    I can buzz the sub speaker wires through and find the 12V switched with a multimeter, but how the heck do I work out which pre-out is which (and the shield).
    Cheers all.
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  10. dualmono21
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    dualmono21 Well-Known Member

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    [Jul 8, 2013]
    im quite surprised theres no adaptor available on the market there usually is
    have you spoken to a good independant car audio store ???

    if you still cant source a lead its possible to do it yourself
    youll need an oscilloscope and a 1khz and 50hz test tone recorded onto a disc at 0db referance

    set the oscilloscope and you should see a wave format , when you increase volume the wave form should increase and when you turn it down it should go down
    use the fader and balance controls to tell you which signals are for which speakers
    the shields are usually all connected to ground so its possible to narrow that down by using a multimeter again
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  11. s8craig
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    s8craig Active Member VCDS Map User

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    [Jul 8, 2013]
    I think you need a 6 channel setup as the A4/A5/Q5 has center and sub speakers driven by the amp.

    Multi-pin connector, 32-pin (T32h)

    1 - Terminal 30
    2 - Terminal 31
    3 - Subwoofer in rear shelf -R157- (+)
    4 - Front left loudspeaker (+)
    5 - Front right loudspeaker (+)
    6 - Rear left loudspeaker (+)
    7 - Rear right loudspeaker (+)
    8 - Centre mid-range and treble loudspeaker -R158- (+)
    13 - CAN bus High (Infotainment)
    14 - CAN Bus Low (Infotainment)
    15 - Subwoofer in rear shelf -R157- (–)
    16 - Front left loudspeaker (–)
    17 - Front right loudspeaker (–)
    18 - Rear left loudspeaker (–)
    19 - Rear right loudspeaker (–)
    20 - Centre mid-range and treble loudspeaker -R158- (–)
    23 - Signal (+), rear right from radio -R-
    24 - Signal (+), rear left from radio -R-
    25 - Signal (+), front right from radio -R-
    26 - Signal (+), front left from radio -R-
    28 - Signal (–), rear right from radio -R-
    29 - Signal (–), rear left from radio -R-
    30 - Signal (–), front right from radio -R-
    31 - Signal (–), front left from radio -R-
    #10
  12. StuBill
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    StuBill New Member

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    [Jul 8, 2013]
    Thanks very much guys. I was kind of resigned to having to test out the signals with DVM/scope, but that pin out table looks spot on for the B8 CAN Bus amp :thumbsup:
    Haven't been able to find any off the shelf adaptor either online or through local car audio specialists unfortunately.

    @s8craig - yeah, I think your spot on with the 6 channel set-up. I could live with loosing the front centre speaker and going for 5, but I believe leaving that out will loose the Bluetooth phone audio which is a PITA.

    One other quick question (excuse my ignorance), on the audio signals from the head unit, I notice each line has a dedicated negative. Is that effectively the same as individual 'shield' lines for each channel - so correct to connect them to the outer of an RCA ?

    Cheers.
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  13. dualmono21
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    dualmono21 Well-Known Member

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    [Jul 9, 2013]
    yes thats correct
    i would however ensure they are individual as they could be fused to stop any earhting problems from coming back up the rca,s and destroying the main board of the headunit or amp
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  14. StuBill
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    StuBill New Member

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    [Jul 9, 2013]
    Great, thanks again dualmono.
    I'll be sure not to common the line level negatives up, and will keep them separate for each RCA.
    Cheers.
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