After market head unit p38

[wayneg]

My latest project a late 99 P38 has no Stereo head unit installed. It appears an after market unit has been fitted in the past. Having done some reading I see there can be problems getting the door amps to spark into life with an after market unit. Has anyone fitted an after market unit? If so any problems and if so how were they overcome. I am not interested in fitting a second hand original and dont care about controls on the steering wheel. I hope to fit something with bluetooth, MP3, and front Aux and USB inputs.

[Scouse]

What model Range Rover do you have?
Some only had a basic sound system & used a garden variety Eurovox head unit.

[wayneg]

It has the Harman Kardon setup with 3 speakers and amps in each door + Sub in the back. Its a late 99 4.6

[3toes]

Think you need to have a look around the internet. Seem to remember seeing something about needing some kind of adaptor to connect to a non standard head unit. Not sure why thisd was though. Also that there are differences between the two head units that were fitted and this will impact on what you need. This is though from memory so may be wrong or incorrectly applied.

[Jezzaol]

I fitted one to my P38, I had to track down which original wires powered up the amps and I then hooked them up to Ignition, chopped the original plug slightly and it fitted to the loom I had, I also got the radio antena adaptor from Jaycar.

Cheers and hope that helps

[wayneg]

I am getting there slowly and have found out that there is a grey and black wire on the original radio wiring that is the power feed for the Amps. This can be connected to the blue, electric aerial power lead from an after market head unit and switches on the amps with the head unit. The speaker outputs need to be attenuated before reaching the amps (whatever that means). My understanding is the speaker output from the after market unit will already be amplified so needs to be Un-amplified. Without the attenuator this will cause interference and high volumes with low head unit volume. There is a circuit diagram on another board that describes how to make the attenuator involving 5 separate resistors. I have e-mailed this to an electronics wiz I know and he says its unnecessarily complicated and my understanding from his reply is a 580 ohm resistor across each of the speaker wire + and - will work. I am now awaiting confirmation from him.
Any views on that?

Wikki, An attenuator is effectively the opposite of an amplifier, though the two work by different methods. While an amplifier provides gain, an attenuator provides loss,

[wayneg]

Have just got the info back on where the resistor needs to go. It goes inline on the + pos wire of each speaker feed between head unit and amp. The Ohms resistance is not critical and might need to be different for different powered head units. The advice was to start with a 330 ohm 1w resistor, then if still to loud increase the resistance to 580 ohms or more. Sounds very easy and better still cheap.

[rathies]

if your amps need an 'attenuated' signal just use the RCA signal outputs on the deck instead of the speaker connections. it will give you the right signal, all you will need to do is buy some rca plugs from jaycar or similar and solder leads onto them. assuming you buy a 'good' head unit it should have front, rear and sub rca's.

[wayneg]

My unit only has RCA`s for fronts not rears so this is not an option for me. As the 4 Resistors are only 10c each from Dick Smith Its almost free.

[p38arover]

Have just got the info back on where the resistor needs to go. It goes inline on the + pos wire of each speaker feed between head unit and amp. The Ohms resistance is not critical and might need to be different for different powered head units. The advice was to start with a 330 ohm 1w resistor, then if still to loud increase the resistance to 580 ohms or more. Sounds very easy and better still cheap.

No.

You need an impedance matching attenuator network.

The diagram for such a circuit was written up on the Rangerovers.net forum in the P38A section.

[wayneg]

No.

You need an impedance matching attenuator network.

The diagram for such a circuit was written up on the Rangerovers.net forum in the P38A section.

With due respect, As I dont have a clue I have sent the above mentioned circuit diagram to a friend who is a master electronics engineer from the USA Bob Terry. (We both have similar extremely complex cars, Mercedes R129 SL500 roadsters). He is renowned for his expertise in motor vehicle electronics and is acknowledged as the most knowledgeable in this field on the Mercedes website Benzword.org. It is to him I have sought advise and it is his interpretation of the circuit being unnecessarily complex. He has given me the info regarding the resistor required. Make of it what you will. I will be using his advice.

Reply fro Bob Terry
That "pi" attenuator is designed for radio frequency signals! It will work fine for audio, but it is unnecessarily complicated.

Those 3 120-ohm resistors are in parallel, so their effective resistance is 40 ohms. The designer surely went with 3 resistors instead of one for the added power handling. At any rate, those 120-ohm resistors serve no purpose in an audio application.

The 47-ohm resistor is also not needed for audio.

You only need the 330-ohm resistor. Actually, since the 47-ohm is eliminated, you probably ought to have a value approximatedly double 330 such as 580, 620, or 680.



2nd reply
The 580 goes from the "+" of the speaker wire to the "+" input on the amp. The value of the 580 is not critical...But its optimum value depends on how powerful the head unit is: more powerful = larger resistor. Since resistors are really inexpensive, I suggest getting 3 values: 330, 580, 1.2K. Those are approximations, so no need to get exactly those values.

3rd reply after thanking him for the info
It's simple, neat, and easy to put a resistor in series with a speaker lead. Hopefully nobody has gone to the fuss of building that "pi" network!

[M.Allison]

G'day,

I have fitted an aftermarket sound system to my p38 its around 146DB lol, My background is i have installed sound systems for 4 years now and have had a fascination with sound for around 6. I have spent over 10 thousand on my sound systems 5 of which was on my rangey. :wasntme:

This is what i did,

I bought a new JVC head unit $380 and some front splits $200 and a set of rear splits is advisable but not necessary coaxial $80 will be fine. I would recommend getting a small speaker amp for $180 - 200. then run new speaker wire (you should be able to get that free) then all you need to do is run the RCA from your "fronts" if thats all you have, to your speaker amp and run all 4 wires from the fronts of the amp (because unless you are watching a DVD movie with 5.1 surround it makes no difference).

so all up it will cost around $720 including the head unit and the necessary wire i can guaranty you it will sound unbelievable.

The reason why i suggest this is because no one really understands what the major difference an aftermarket sound system sounds like compared to "stock".

Thats my 2 cents.

Thanks Mike

[p38arover]

With due respect, As I dont have a clue I have sent the above mentioned circuit diagram to a friend who is a master electronics engineer from the USA Bob Terry.

Reply fro Bob Terry
That "pi" attenuator is designed for radio frequency signals! It will work fine for audio, but it is unnecessarily complicated.

I don't know what a master electronics engineer is - many jobs overseas have the name of "engineer" attached to blokes who do servicing, e.g., field engineer. They are not engineers.

I disagree that pi networks are for RF. We always used them to attentuate audio in telecomms circuits when I was doing that stuff many years ago. Using a pi network allows impedance matching and accurate level adjustment. Merely using a series resistor means you'll be mucking around getting the right value to do the job.