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Premium Member
1997 P38 4.6 HSE
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14 Posts
Discussion Starter #1 (Edited)
** Edit ***
I have found that the buzzing only happens when I turn on the running and/or headlights. At least I know the amp isn't blown and I can find a solution. If anyone can save me time, please feel free to pipe in
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I just got done sorting out connecting a new double DIN head unit to the original door amps and speakers. I’ve read up on need of attenuators and that results vary depending on original head unit. I have no idea what that is or the color of the clip (pink or not) because both were missing. I thought my amp wire pairs were cut elsewhere too until I realized I needed to run switched power to black/greys to wake the amps. Boom! Great and loud sound- sub and all! I figured I must have the system that plays nice with high-outs of new HU’s because I didn’t hear loud whining. I did get some low level rpm whine, but I could live with it or try ground strapping the HU or other noise eliminator. Any thoughts on this is welcome.

So, I found the loud buzzing only happens when I turn the running and/or headlights on. This is great news after a huge disappointment to arrive home from jamming around the block to find a loud buzz. I turned my lights on mid-drive, but didn't notice due to loud music. I am sure I can find a solution for this, but advice is very welcome.

Specs of the state of current install and wiring:
-New Kenwood mechless double-DIN
-Original HK amps and speakers - 11 speaker system - sub is black plastic box with no visible woofers.
-New head unit was wired with an unknown constant power source that was done before me and tapped to original harness for switched power, ground, and illum. The large ground strap is not connected, as I didn't know yesterday what it was for.
-I tapped the switched power to the black/greys to wake the amps. Perhaps I should first try this from the amp wake out on the new head unit?

UNKNOWNS
There is a relay wired from taps into the original power ISO harness. I don't know what it is or what it does. MAYBE this has something to do with the EAS disable spring replacement in the truck. I haven't traced wires, but there are photos in my other "Hot-wires and gremlins" post. The relay taps to a purple with red trace into the constant 12v, while another red with blue trace taps into the switched power. I have yet to figure either.
 

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549 Posts
There's plenty of threads on this subject on here and Landyzone. You have three choices:
  1. Install 5 proper audio balancing transformers between the Head Unit Line Out & the HK amplifiers. (result = no buzz & perfect sound)
  2. Experiment with attenuators and other bodges between HU speaker out & HK Amps to get it working as best you can. (results = various)
  3. Put up with the low level buzz and don't use the lights !! (probably not legal anywhere)
 

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Premium Member
1997 P38 4.6 HSE
Joined
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14 Posts
Discussion Starter #3
Thanks for taking the time to read my post and reply. I haven't checked Landyzone.

Connecting the actual amp-waking power out from the new head unit to the amp-waker gray-black wires SUBSTANTIALLY reduced that buzz from the lights. However, the wine is more noticeable now, and after driving for an hour today, certainly a no-go. I'm currently connected to speaker outs and seem to max at 50% of the total volume range where the sheer loudness is too much too handle, rather than distortion being the problem. I have yet to try line-out. The ads say it's 2V. It's a Kenwood DMX4707S. I remember a thread saying the original HK wants 3V? it seems like I'm only getting the whine on on the front passenger side, which is the only wiring I investigated and messed with. I noticed a lot of system wiring clusters in and around that front corner of the car and that wire cluster going to that door. Perhaps there is interference noise? Perhaps I just need a ground loop eliminator for power? The unknown in this situation yet is that I still haven't traced the source of the power feed that was hacked in. Am I better in the long run to go with the line outs with balancing transformers? Literally, the audio sounds fantastic, albeit over-juiced. I'm somewhere between not easily impressed and audiophile as reference.

Thanks again for taking the time.
 

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1995-2002 Range Rover P38A
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190 Posts
The number one thing to do first is to check all your grounds.

Every piece in the system needs to be securely earthed, preferably to the same point on the chassis. My car doesn't have door amps, so I've never done any measurements but I reckon there will be voltage differential between the chassis and the door frames. Tie everything in the system to the one, secure, tight, bright and clean earth point somewhere then go from there.

First principles, first.

Solder and heat shrink everything and use good shielded cable for the low level signals. It may not cure the fault but it's the only way to wire it all up.

Tom
 

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LEGACY VENDOR
1995-2002 Range Rover P38A
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4,199 Posts
If you've connected the head unit amplified outputs directly to the amplifiers as they are, then you're over-driving the amplifier inputs. Either make up the attenuator circuits (google or search on here for Ray Ambler P38 Attenuator, or something like that - he was the guy who first devised them), or put in some line isolating transformers and run off the RCA pre-outs.

I've used both, and the attenuators are easy to make and work well. I've actually just switched to line isolating transformers, and I now have a slight detectable whine on mine, but I need to check some of the grounding still as I've moved things around up front lately!

Currently you are amplifying and amplified signal - which won't be helping with the volume of your whine either.
 

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Premium Member
1997 P38 4.6 HSE
Joined
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14 Posts
Discussion Starter #6
Thanks a lot for feedback. I think I will try balancing/isolating transformers on the pre-outs or by a cheap unit that does that and allows increasing voltage of the pre-outs just in case.

Now to figure out the best string wheel interface. I am definitely missing quick buttons without looking. My unit is a non-manual button touch only, so I'm definitely feeling unsafe and tedious about using touch-screen volume. I'll do my obligatory searching for the recommended unit for that :)
 

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Premium Member
1997 P38 4.6 HSE
Joined
·
14 Posts
Discussion Starter #7
There's plenty of threads on this subject on here and Landyzone. You have three choices:
  1. Install 5 proper audio balancing transformers between the Head Unit Line Out & the HK amplifiers. (result = no buzz & perfect sound)
  2. Experiment with attenuators and other bodges between HU speaker out & HK Amps to get it working as best you can. (results = various)
  3. Put up with the low level buzz and don't use the lights !! (probably not legal anywhere)
Thanks for the feedback
 

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Premium Member
1997 P38 4.6 HSE
Joined
·
14 Posts
Discussion Starter #8
If you've connected the head unit amplified outputs directly to the amplifiers as they are, then you're over-driving the amplifier inputs. Either make up the attenuator circuits (google or search on here for Ray Ambler P38 Attenuator, or something like that - he was the guy who first devised them), or put in some line isolating transformers and run off the RCA pre-outs.

I've used both, and the attenuators are easy to make and work well. I've actually just switched to line isolating transformers, and I now have a slight detectable whine on mine, but I need to check some of the grounding still as I've moved things around up front lately!

Currently you are amplifying and amplified signal - which won't be helping with the volume of your whine either.
I'm going with the same PAC SWI-RC unit you used for steering wheel and a couple PAC SNI-1's for the isolating transformers. I'll post an update after all is installed.
 

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549 Posts
I used five of these transformers Z1604 | Through Hole Audio Transformer 600Ω 2mW | RS Components based on frequency response, etc. Those "PAC SNI-1" provide isolation, but not true balancing unless you fully isolate the output RCA from grounds.

My transformer Primary is connected to Head Unit RCA outputs. Secondary outer connections go direct to Harman Kardon Inputs, with centre tap unused. This way you get some step-up on the signal. Secondary winding is NOT grounded.

Transformers should be close to Head Unit, because you get more noise ingress on the RCA wiring than the balanced pairs. Use twisted pair to connect to the original 10-pin HK HU connector, so you then have proper balancing all the way to the door amps.

Also I re-checked all the door amplifier grounds and sorted any that were bad. Usual kick panel connector issues. Finally double check that the Head Unit RCA connectors are properly grounded, and also the HU chassis.
 
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