Pink noise-like hiss problem

[VmanJeff]

Hi all! New to the forum but have been 'lurking' for a time as I re-educated myself. I hope someone can point me in a new direction on this problem...

Car...Pontiac ***** Am

Stereo... Alpine iDA-X100 HU

Imprint sound processor

Kicker 500W sub amp

Kicker 4x90~W amp (at 2 olms)

1 farad cap

Stealth sub box

Amps 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. NO hiss (that I can detect) through the subwoofer. 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 (but remember, no sub noise) 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. I ran it like this for a short time.

I could go on and on...sorry to be soooo long but the more info the better in some cases, I think! Anyway, I am was hoping for some ideas I might not have thought of... Thanks for ALL replys!!

Jeff

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[VmanJeff]

Quick update here....

The noise IS hearable through the subwoofer with the gain all the way up. It was not auidable wth normal gains.

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.

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.

Any other thoughts??

 

[VmanJeff]

Update 2...

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...!!

As always.....any thoughts here?? Or am I typing to myself //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif

Jeff

 

[ace_800 5,000+ posts]

I would suspect the HU as well, if you have switched out the RCA's and etc.

Also, IMHO lose the cap and do the big 3.

 

[DidUHearThat? 10+ year member]

IMO, it sounds like you have your gains set incorrectly. A small amount of hiss is normal, but should not be very noticeable.

You can either set the gains with a meter, or by ear. To set it by ear, turn the gain all the way down, then turn the H/U volume up to 70%. Then slowly turn the gain up till you hear it distort, then turn it back a little bit.

Now the hiss should be gone, and your head room should be near even throught. When your HU is running near max, your amp should be too, and no hiss at lower levels.

 

[VmanJeff]

IMO, it sounds like you have your gains set incorrectly. A small amount of hiss is normal, but should not be very noticeable.
You can either set the gains with a meter, or by ear. To set it by ear, turn the gain all the way down, then turn the H/U volume up to 70%. Then slowly turn the gain up till you hear it distort, then turn it back a little bit.

Now the hiss should be gone, and your head room should be near even throught. When your HU is running near max, your amp should be too, and no hiss at lower levels.

I thought this too....at first...but I set and re-set the gains til I felt I had a handle on the proceedure and how is should sound. I do not have a meter but I used the method you describe and used diffrent music along the way. I understand a small amount of hiss is normal and it should be covered by normal driving, but the amount I was getting was hearable while driving at moderate listening levels! And my car has a souped up 350ci with headers and LOUD exhaust, etc. etc. It was set-up for drag racing. Also, when I switched the HU's the hiss level was much lower with the same gains so I thank you for the thought. I am by no mens an expert with the gains but I think I am getting a better understanding as I troubleshoot.

One think I find ironic.... I spent my whole life in the chase for NO NOISE in my audio and home theater (or 'as good as I can get' fidelity) only to come full circle and have to put up with this again! Burn all tapes and records! JK...but you get my point...! I compress all my audio at at least 196kbs and know what original recording hiss sounds like so I initially thought...my God, did I create a car audio system with such high level of fidelity that I now hear mp3 sound for what it really is!!??? Silly consumer.....Not with these components!

Thanks for the replys!!

Jeff

 

[VmanJeff]

I would suspect the HU as well, if you have switched out the RCA's and etc.
Also, IMHO lose the cap and do the big 3.

Ace-800.... I just learned about the big 3 and will get to tis this weekend... I have a high volume fuel pump which recommended basically double grounding the battery to the frame so this part is done. I can do the other 2 without too much trouble... but why loose the cap?

 

[ace_800 5,000+ posts]

There is a thread on the forum that goes into depth on why, but basically it is just making your alt work harder for charging the cap and the battery. With your setup, since it is not to much power, with doing the big3 you will get better current running though you vehicle and not have dimming.

 

[VmanJeff]

OK Ace_800...I will work on the big 3 tomorrow......but now for something completely different......!! //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

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 "DidUhearThat" 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.

Thanks for the posts and I hope this helps someone out there!

 

[DBfan187 5,000+ posts]

hiss is usually a gain issue