Owners who want to install an aftermarket stereo
head unit wth more modern capabilities in their 1995-2002 Range Rovers
are frustrated by the fact that most replacement head units are
incompatible with the rest of the Range Rover stereo system -- namely
the built-in amplifiers that drive the multitude of speakers, and the
steering wheel controls. Ray
Ambler, a Rangerovers.net member, has pioneered the process of
interfacing these aftermarket units and has kindly provided the
information on this page for making the
built-in P38 stereo amplifiers and steering wheel controls work with
any head unit. Ray's
solution allows you to use the built in
amps on a standard high level output from basically any stereo head
(Skip this if not interested!)
The input impedence of the Range Rover's Harmon Kardan door amplifiers
is approximately 70 ohms. This is why
when you drive them with the full output from the usual aftermarket
head (with an output impedance of 4 to 8 ohms) the
volume has to be kept low. The "low power" original Alpine unit has an
output impedence of about 70 ohms and this is what confuses most
installers. When you use the line out feeds (1000 ohms or above) you
will get hissing / interference or just low volume.
To solve this problem, you need to create
an attenuator capable of giving a suitable load to the head unit,
provide matching to the door amps and reduce the audio level by 20dB.
Easily done with a pi or T attenuator. Remember that the attenuator has
to handle the power from the head unit. In my case I tested the head
unit into a 16 ohm load and it was fine. This means that full volume
requires the attenuator to handle about 2 watts making it small and
easy to build using 1 watt resistors in series / parallel
configuration. Remember to use carbon or metal film components, not
wire wound or you will produce undesirable inductive loading.
Instructions for Assembling the Interface
1. Purchase an ISO male to ISO female head unit lead from a motor
factor or car audio stockist.
2. Construct 4 off the circuit shown. Parts from Maplin or similar.
Use carbon or metal film resistors, not
3. Cut each speaker pair of wires in turn and connect in the circuit.
4. Repeat for the other 3 channels.
5. Insulate the components so as not to short onto anything when
You now have an inline adaptor lead that will attenuate the speaker
level to the correct value and provide impedence matching for the head
unit and HK door amplifiers.
Plug and Play!
Setup and Testing
For owners with the DSP system (Amplifier by
in doors), it must be pointed out that the original head unit volume
must be turned up to set high volume on the DSP amplifier prior to
removal. Ignoring this easy step will result in poor volume from the
aftermarket head unit.
As a guide to volume levels with the
attenuator fitted (4 needed),
my volume goes from zero to 50. level 8 is fine for gentle listening.
level 30 is mindblowing. Any higher is clear but should be listened to
from another county / state! The JVC headunit has a software menu that
limits the max volume to 30
Wheel Control Interfacing
Note that most aftermarket head units may
not allow immediate control from the Range Rover's steering wheel
buttons. However this problem has also been solved by Ray Anderson.
Steering wheel interfaces are available for all later Alpine
equipped P38a to allow full use of the buttons. Ray specified the exact
requirements and worked with www.nexxia.co.uk
who now produce the necessary interface. Ray's prototype, interfaced to
a JVC head unit has been perfect since install over 12 months ago.