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      09-10-2019, 07:07 PM   #1
lewiszman
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Question Z4M with DSP - Aftermarket Head Unit, OEM DSP and Speakers - Check my work

Hi guys,

I've been scouring the interwebs for someone else's hard work in a solution for installing an aftermarket head unit while retaining the factory DSP amp and speakers. One method was to splice the factory radio into the DSP, leave it in the trunk. Didn't appeal to me, and I looked for a cleaner solution without luck.

I've developed a plan, could you guys check my work below and let me know if I've missed or misinterpreted something?

Here are the assumptions:
- The car is a 2006 Z4M
- The car is not equipped with a OEM CD changer
- Aftermarket head unit will be an Alpine ILX-F309 "Halo9" with the following RCA pre-outs: 2-channel Front, 2-channel Rear, and 2-channel Sub
- We are keeping OEM DSP amp, and speakers
- We don't want to splice in a factory head unit and keep it in the trunk


1. The biggest issue seems to be the DSP's input is a RG174 coax cable rather than the standard RCA pre-out inputs you find on aftermarket amps.

2. As such, virtually no aftermarket head units have coax pre-outs. So we have to convert the RCA pre-outs to a coax signal/connector.

3. Grom Audio sells a DSP adapter (link) that converts signal from a 6-pin connector to coax.

4. We cut the RCA pre-outs on the Alpine HU, pin it out to a matching 6-pin connector on the Grom unit, which gives us a coax connection to the DSP.

So my question is... Is my plan sound? (pun intended). I'm not an electrical or audio specialist, so I don't know if the differences are just the connections or if there is a difference in signal as well.

Please advise, interwebs! Thank you!
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      09-10-2019, 07:59 PM   #2
GuidoK
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1. Have you actually looked at if your amp uses the coax cable with the amp?
Most DSP amps don't use the coax input. Afaik all DSP amps have the physical input, but if its not used, it also doesnt work. My guess its programmable to use or not (probably with ncs expert).
If the coax imput is used, its afaik only used with the CD, as the coax runs from cd changer to amp (the headunit doesnt have coax out).
For the rest the amp has normal line inputs. you can look up the wiring in WDS.
I think DSP amps in cars without nav mostly use the coax input.
2. the biggest issue is not to use coax/dsp input, but having your amp switched on when the HU also switches on. The amp gets a signal to turn on. I dont know if this is via Ibus/Kbus or if its a dedicated hi/low line as used in aftermarket amps.
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Last edited by GuidoK; 09-10-2019 at 08:11 PM..
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      09-11-2019, 08:42 AM   #3
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The following applies to the Top HiFi with NAV, DSP and Carver subs system. I do not know if this is true for the other audio options.

Volume control take place in the factory amplifier. The factory head unit digitally communicates (via the KBus as I understand it) to the amplifier and tells it to increase or decrease the amplifier gain. If a factory head unit is not connected to the amplifier, you will not be able to adjust the amplifier volume (gain).

If you could just set the amplifier volume to full, leave it there and then connect a non-factory that might seem to be a solution. But you can't do this. The factory amplifier volume is reset every time you turn off the car. Try this, play a tune at a loud volume and turn off the car. Now restart the car...volume is reset to a lower setting.

If you are going through the hassle of replacing the head unit, then go the extra mile and replace the amp and speakers. In the end you will get an immensely better sounding audio experience.

Last edited by elerner61; 09-11-2019 at 08:47 AM..
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      09-11-2019, 10:17 AM   #4
GuidoK
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Quote:
Originally Posted by elerner61 View Post

If you are going through the hassle of replacing the head unit, then go the extra mile and replace the amp and speakers. In the end you will get an immensely better sounding audio experience.
That can get quite expensive. There are 10 speakers individually controlled.
You'd either need a 10 channel full DSP amp or 2 5 channel full DSP amps if you want something similar to the existing system
I think especially with the amps a lot of quality gains can be made, TBH I think the speakes are quite good.
Especially to get a woofer into the small carver enclosures that is suited to that space (in regard to Thiele-Small parameters) is quite difficult. That requires some extensive modelling.
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Last edited by GuidoK; 09-11-2019 at 10:30 AM..
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      09-11-2019, 10:26 AM   #5
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The original DSP amp will not work with aftermarket head units. You will need an aftermarket amp as well. A standard one will do, but you will need to figure out the wiring on the amp connector.

Refer to my post for more info.
https://www.zpost.com/forums/showthread.php?t=1539151
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