Isolated DC power supply ...?

[captainobvious]

I'm almost betting that it is being induced on the signal line... I thought that running my audio lines around the same path of the factory harness would be a tidy-neat way to do things...... Boy, was that a bad move.

Well that's a bitch if true. Although...using the same signal path of RCA's to the back, when I use just the HU with no line driver after it, I don't hear the noise. Which would make me suspect that the either (A) The noise is just below audible level and when gain is boosted, I'm pushing it into that range, or (B) the line drivers ground isn't isolated and/or the unit has an issue? I suppose the best way to test would be to connected it to a separate power source like an external battery and see what happens...? Thoughts?

[chad]

Well, if the line driver has a differential input then it could be amplifying shit that is running up and down the shield.

In the end I HAD TO move my signal lines and ran them smack down the passenger side footwell. But hondas are an electrical bitch, especially ones made in the UK..

[cajunner]

so, no noise at all when taking the line driver out?

maybe it's one of those "connect the ground/shield on one end of the RCA plug" fixes.

since, you're one component extra in the from, to, from to sweepstakes.

or you could just run an isolated source (mp3 player) into the line driver and see what gives, and then bring the line driver to the trunk, stick a couple of little wires to the amp's power terminals, and fire it up back there using both the signals (alternatively) from the deck and mp3 player.

[captainobvious]

CAJ- Good troubleshooting tips. I'll give these a shot. TBH, I haven't tried running a zero db track and pumping up the volume yet, but I haven't heard the noise at zero volume or any of the range in normal listening like I was hearing with the line drive rin the chain. I'll also check this as that will be important in determining if I'm getting the noise from the source and amplifying it with the gain stage of the Tru piece.

Chad- I haven't taken the cover off of the Tru Line8 yet to see if it has a selectable ground/isolation/"x" ohm switch or pins, but it's possible it does. I better have a look in there. Unfortunately, I have found ZERO documentation on this piece on the web (bought it used). I'll post up what I find.
You guys rock, thanks!

EDIT:
I also remembered that I have an Audiocontrol Matrix 6 channel line driver which I know for certain has the selectable grounding/isolation options too sitting in the closet. I'm going to troubleshoot the issue first though to see why I'm getting the noise before I bring more equipment in to further complicate things.

[chad]

EDIT:
I also remembered that I have an Audiocontrol Matrix 6 channel line driver which I know for certain has the selectable grounding/isolation options too sitting in the closet. I'm going to troubleshoot the issue first though to see why I'm getting the noise before I bring more equipment in to further complicate things.

I had one of those, it rocked.. but the audiophools would hate it because it used 4560 op amps IIRC. Maybe 4580's

[cajunner]

I like to think ground loop when encountering alternator whine, maybe a DMM check of your potentials would show something, but usually not unless it's bad.

if you're powering the deck off the factory power circuit, then the line driver has a different ground, that could be all you need to know.

[captainobvious]

Both the deck and the LD were supplied by a shared direct 4ga power run direct from the battery and a 4 ga ground to a location on the frame in the cabin nearby. I had also tried grounding both units to the same location of the amps and also tried grounding the head unit separately- neither of which solved the noise problem.

In other news, I just took off the cover of the TRU Line8...there is no setting for ground isolation. I'm assuming it's either built in to the circuit, or there isn't any. In addition, I just ran my zero bit test track (this is with only the HU connected in the signal chain) and from 0 volume all the way up, with the accessory position on first and then with the engine started and while revving. No noise is audible, even with my ear to the mid/tweet. So this seems to finger the line driver as I would think I'd hear SOME sort of noise through the speakers at high volume in the worst of conditions if it was originating from the source.

[captainobvious]

I had one of those, it rocked.. but the audiophools would hate it because it used 4560 op amps IIRC. Maybe 4580's

Pssshhh
.005% THD, FR of 10hz-100Khz +/-1db, and S/N of -110db in it's stock form pretty much says all you need to know. You're not making audible improvements on that.

[PaulD]

why do you NEED the line driver ?

And yes, I have fiber out on the deck and fiber in on the processor - makes life easier.

[captainobvious]

I guess technically I don't "need" it. I wanted to maximize my signal voltage before sending back to the amps to reduce noise and keep amp gains at minimum. My HU does clip at a volume just above where I like to listen to it at. So making sure I have adequate voltage out and avoiding running into that clipping range is crucial.