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1995-2002 Range Rover P38A
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Discussion Starter #1
2001 Vogue with HK Premium Sound System and (binned) Sat Nav.

I'm trying to diagnose a fault in my DSP (not output to the subwoofer). My electronics knowledge is a little sketchy but I think I see what most of the components on the DSP board do but I'm having a crisis of confidence over how the DSP and head unit interacts with regard to volume, tone controls and subwoofer level.

Clearly the head unit outputs two line out signals to the DSP and the DSP uses a bunch of op amps to filter these signals and then feeds them to 16 separate amplifiers to drive the various speakers (two per door x 2 channels). The sub-woofer amp is in the subwoofer box so the DSP sends it a line out type signal, but the filtering appears to be done in the DSP (a few more op-amps - If you put a normal audio signal into the subwoofer you can hear the full frequency range).

So far so good but how does the head unit control volume / tone / balance / fade / subwoofer level and DSP mode? I think they communicate digitally and the DSP uses a DA converter to control the frequency response and gain of the filters. Have I got this right or does the head unit control the gain and tone etc.?

Looking at the circuit diagram I can't see anything that looks like a comms bus between the head unit and the DSP (which is why I'm having the crisis). There is a wire from Pin 10 on C0922 (the 'extra' connector on the head unit) to Pin 27 on the DSP is that it? The ETM seems a bit sketchy over this connector (it's in two halves 0921 & 0922) but I can't see some of the supposedly populated connections on the diagram. Is this my missing databus.

Can anybody point me in the right direction?
 

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1995-2002 Range Rover P38A
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1995-2002 Range Rover P38A
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121 Posts
Discussion Starter #3
Thanks very much for that. The discussion on that thread suggests pin 10 is indeed my missing data bus. Marty suggests that the 'undocumented' wiring includes an analogue subwoofer output from the head unit to the DSP. I shall be investigating those in the morning! Does seem rather odd to use a separate analogue input for the sub but use the DSP to implement the fade function.
 

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1995-2002 Range Rover P38A
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Sounds like you are on to it. I just had to laugh when you mention something which is indeed odd as being "Odd" on a P-38.........Odd and P-38 engineering are synonymous!
I will be curious as to what you find out, having a dead HK premium system as well
 

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1995-2002 Range Rover P38A
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Discussion Starter #5
"Curiouser and curiouser" Cried Alice.

I've been doing a bit of further investigation by connecting the audio outputs from the head unit to an external amplifier. I've come to the following conclusions.

The left and right audio outputs from the head unit on C0092 are indeed line outputs and the voltage level (volume) is not affected by the volume setting on the head unit. My ears also tell me that these outputs are not affected by the bass, treble, balance, fade and subwoofer settings. This is not a huge surprise as we know that the DSP must provide the fade functionality. Given the sophistication / complexity of the DSP it's not surprising that HK chose to do the tone control with it as well.

There is indeed an audio output on pins 1 & 4 on C0921 (subwoofer output according to Marty). The signal level is affected by the head unit volume and the subwoofer settings. As best as I can tell the frequency range of this output is the complete audio range i.e. it is not filtered to remove the high frequencies. I can't hear any effect on the tone controls on this output.

Now for the Alice in wonderland bit. This 'subwoofer' output from th head unit is connected to pins 39 & 40 on the DSP but, wait for it, these pins are not connected to any circuitry on the DSP board. I've checked at least four times and can find no continuity between these pins on connector C0491 and the headers that are on the main DSP board. The DSP uses a daughter board at right angles to the main board to connect the rather oddly laid out connector to the two layer headers on the main board. Unfortunately this daughter board appears to have at least 4 layers so I can't visually trace the tracks. Whilst this may seem strange at first I think there may be an explanation. The head unit is made by Alpine whereas the audio system was designed by HK so maybe HK had to live with what the head unit gave them and decided not to use the subwoofer output from the head unit but rather to produce it within the DSP themselves. This also explains why this wiring is not shown on the P38 ETM i.e. it doesn't do anything so it would be confusing to show it.

All very interesting but hasn't got me much further with fixing my DSP.
 
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