want your insite on hiss issue

Hi all! New to the forum but have been 'lurking' for a time as I educated myself. I hope someone can point me in a new direction on this problem... I originally posted this to another message board but have no replys and after reading on this board about problems similar to mine I decided to post here and see what might be said.  Sorry for the length ....!  Hope someone can help!

Car...Pontiac Trans AmStereo... Alpine iDA-X100 HUImprint sound processorKicker 500W sub ampKicker 4x90~W amp (at 2 olms)1 farad capStealth sub boxAmps mounted on rear wall rack. Power for amps runs down drivers side to top part of amp rack, to the cap then to both amps, and is 4 gauge. Grounding is 4 gauge and in 2 seperate places on rear of car. Ai-net cable to Imprint runs from HU across passenger side dash then down passenger side to Imprint unit under pass seat. RCA's run from Imprint down passenger side to rear amp rack behind bottom of rack to amps. Speaker wire runs from bottom of amp rack back down passenger side to pass rear speaker and both front speakers. Drivers side rear speaker runs down bottom of amp rack then as far away from the power cable as possible to speaker. All HU and imprint power and ground through wiring harness w/ extra ground. Amps well grounded to rear metal of car. All cables run under carpet in car split tubing. Whole interior dynamatted. My probem is pink noise type or interstation FM-like hiss through all 4 speakers, fronts and rears and the sub channel. With car OFF and no input to the HU (In USB or i-pod mode) with the HU at 0 volume, no hiss...with HU volumes above 0 increasing hiss with the pronounced rise in the last 1/4 volume. I turned the 4 channel amps gain down for now and the hiss is much less but I think this is a bandaid because I think I have more headroom here. I tried running different RCAs from the Imprint module to the amp with same result. If I unhook the RCAs from either the amp or the Imprint the hiss goes away. I took the cap out of the chain but this did not help (I did not think it would). I am hooking up another HU tomorrow to see if it is the HU. And while I am at it I will try a RCA direct connect from the HU to the amp to see if the Imprint is causing it. After that I will try another amp and Imprint (if I can find one). I do not think it is a wiring issue except for possibily the Ai-net cable or the speaker wire to the drivers side rear which is close to the amp power wire. I suspect equipment for a couple reasons... The HU was hooked to power without me realizing it throughout the dynamat and interior re-install during which my car battery died so I put my charger on it for the better part of 3 weeks. The HU has also been in and out a dozen times as I messed with wiring, settings switches, etc. The 4 channel amp was purchased at the Circuit City firesale but was new AFAIK. The Imprint came from Crutchfield and sat on the workbench for this install but was initially hooked up as a loopthrough back to the HU RCAs which act as inputs if you don't have an external amp and then the sound is output through the harness to factory wires/amp (monsoon stereo system). I ran it like this for a short time.

Quick update here....(the next day)

Took the Imprint out of the equation and hooked up the HU RCA outs to front, rear and sub and the noise dropped so much as to be typical system hiss/noise. At least thats what I would think is typical. The Imprint changes the HU 2 volt outs to 4 volt but I think this is not the reason for the increased noise, but rather just the amplification of an exhisting problem. I guess I was in denial to think it was not wiring but now I think it is either the Ai-net cable routing OR the power lead connection being hooked up with the HU wiring harness, OR bad ground for the Imprint, OR the Imprint unit itself. Running out of time today so I will start checking these tomorrow. Could also be the Ai-net plug on the HU. I will check that with the extra HU I have.

Update 2...(Yesterday)

Rerouted the Ai-net cable...no change.. Hiss still at unacceptable levels.Tried a different HU (same model) and the hiss was reduced to acceptable levels. This leads me to believe that the original HU is defective. I think at this point I will rule out the amp or the RCA and speaker wiring. I still suspect the Imprint unit but I see no basis for this. Would like to try another one.I am still going to move the Imprints power leads since I am installing the bluetooth adaptor later today. I will tie the power for the Imprint and bluetooth seperate from the HU. I do not expect any change.....but I am learning to expect the unexpected on this install...!!

Thanks for your patience on this LONG post!

VmanJeff

I have not seen this problem on an Alpine deck in nearly 20 years, but you need to at least do the test at the top of the following page. Just do the test with the meter. If it is a new deck, you should try and get it replaced if it does not have ground on the shield of the RCA jacks on back of the unit.

FIRST, the signal and speaker wires CANNOT be the cause of any noise. There is no way for RCA or speaker wires to pick up noise in a car stereo, we've been over that and over that in this very forum. I run ALL of my cables on one side of the car, due to space restraints, and I have no noise. I *did* have noise, but then I found out it was a ground loop, and after properly grounding all components - from the engine bay to the amplifiers - the noise is gone. Now: The X100 really ISN'T an audiophile piece... (Having done some experimenting with it myself, I know this...) Since you said that the noise starts, or becomes more audible when you turn the volume up only one click from "zero" to "one", this should be your first clue to the offending piece. The Imprint is doing just what it is supposed to be doing, it is a pre-amp, and it is not selective in the signal it boosts. Rather than using the Imprint to boost ANY signal, why not just set it for "unity gain", if it is possible? This means that if there are any boost or cut options within the Imprint, simply don't use them, this will give you at LEAST a 3dB cut with the hiss. As I am not familiar with it I can only offer this as a suggestion. Since you mention headroom by name, I think you need to understand better what headroom is. When you turn the gain on your amp down, you are actually IMPROVING the headroom in a system, by not making the amplifier run WFO all the time. Because it makes LOWER continuous output, there is MORE power available in both continuous as well as peak output. THAT is headroom. Not continuous loudness. Almost guaranteed... The hiss you are hearing is in the deck. Not because of any RCA grounding issue, but because that's the way the deck IS.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Thanks to all for the input. 

"I am an idiot"..... The HU does not use the RCA pre-outs to connect to the Imprint module.  It uses a dedicated cable called an Ai-net cable so the RCA's on the HU are not used.  But I will check these anyway just for kicks.  The Imprint unit has RCA 4 volt pre-outs and these are connected to the amps. 

"haemphyst"......  I have read with interest many of your answers to others and hoped you might comment.  The Imprint unit does not have any unity settings.  It 'ups' the output volts from 2 to 4 and It enables Alpines licensed "Audysey" <sp> sound shaping routines.  With an optional mic and laptop program you 'tune' the sound through software for EQ and soundstage.  It also has settings to improve the sound of compressed mp3's and FM radio.  I think it hits the mark as I like the sound I am getting.  My use of headroom was wrong, as you pointed out. I simply ment that I felt the system should be capable of higher volumes as the sound was undistorted at higher gains but the hiss was very iritating, so when I turned the gains down I was not getting LOUD.  Here is what I came up with.

OMG..... I worked all night last evening and had sometime to research. I read lots on the big 3, grounding the RCA outs from the HU and even one where the guy cut the negative side of the speaker leads.

This all got me to thinking....Used to be that cars had a sheetmetal skeleton under the dash and the radio was screwed to it...good ground there!!. Today we have super strong plactic/fiberglass/etc. framework (a 2000 Firebird TA) and the only ground is the one through the wiring harness, so I had a thought....I ran another ground wire from the Imprints ground (on pass side) across to the other side of the dash and tied it in with the ground from the wiring harness, which was already tied in to the harness and the dash. Then I tapped off this ground and ran to another point under the drivers side. THEN I ran 2 ground wires from the chassie of the HU and tied these 2 into the others. And finally, I cut and taped all the harnesses speaker wires which I no longer needed since I was now using the pre-outs.I then finished the bluetooth install and plugged everything back together.....fired her up...set my HU and Imprint levels/settings and ......... NOTHING! Like others have said..... a little bit of hiss is normal....And there was a lil' bit. I needed to turn up the HU volume a bit more to hear it....but, I tell you, I think I solved the issue! I will check the gains on the amps tomorrow and get my final settings worked out.  This was with the 2nd HU and, if you recall, the 2nd HU did not have the levels of hiss I was getting from the original one.Thanks for the posts and I hope this helps someone out there! 

VmanJeff