#1693351 - 08/13/09 08:58 PM
Line Level EQ / Gain control? (Another hissing issue)
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bnovak
SD Ralph Wiggum
Registered: 07/08/09
Posts: 53
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I was just flipping through one of the other posts about hiss, and I think I've got the same issue.
Setup is in my Expedition with the factory amplifier (35x4+85x1 for sub) Had an Alpine CDA9883A replaced it with the IVA-D106. HU is wired via high level (speaker wire) outputs to the inputs of the factory amplifier. Factory amplifier only seems to accept high level inputs as I tried wiring in via RCA out on IVA and got nothing.
Well, long story short, I know have a really bad hiss. I kinda wish I had an alternator whine since sometimes that's easier to track down 
The hiss seems to be a constant level independant of the source volume or source selection(cd/dvd/tuner)it's really most noticeable with the CD or DVD (especially DVD!) since the tuner drowns it out most of the time. The only time it goes away is if I mute or turn volume to zero.
So.....I guess I need to figure out a way to gain down the high level inputs? Can I do this with a passive network or resistors? (sorry, I work in the semiconductor biz but am lousy with analog audio) Or, do I need to find some sort of high level in, high level out gain controller?
Like I said, I tried using a low level signal into the amp but that was a no go, and I am getting (what I can tell is) a clean signal, it just has an over-riding constant hiss. There is no change in pitch, tone or volume with the volume increased on the HU.
And of course, it's a day after I told someone else NOT to use a LOC 
Any ideas? Thanks in advance.
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#1693369 - 08/14/09 12:07 AM
Re: Line Level EQ / Gain control? (Another hissing issue)
[Re: bnovak]
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keep_hope_alive
in another life, i'm a serial killer
SD I Power Bombed the Undertaker
Registered: 04/24/07
Posts: 13370
Loc: Quad Cities, IL
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Pacific Accessory Corporation (PAC) has the correct interface for adding an aftermarket HU to a factory amplifier. buy the correct adapter and your problems are solved.
http://www.pac-audio.com/
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#1693628 - 08/14/09 11:44 AM
Re: Line Level EQ / Gain control? (Another hissing issue)
[Re: keep_hope_alive]
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bnovak
SD Ralph Wiggum
Registered: 07/08/09
Posts: 53
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thanks hope. I'll give that a shot.
like I said, just confused as to why one unit worked fine, and the second unit hooked up exactly the same way wouldn't. Didn't think 1w in power would make that much of a difference!
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#1693722 - 08/14/09 06:07 PM
Re: Line Level EQ / Gain control? (Another hissing issue)
[Re: bnovak]
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keep_hope_alive
in another life, i'm a serial killer
SD I Power Bombed the Undertaker
Registered: 04/24/07
Posts: 13370
Loc: Quad Cities, IL
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do you still have the other HU you can install and see if the problem goes away. if so, it may be related to the new head unit.
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#1693727 - 08/14/09 06:46 PM
Re: Line Level EQ / Gain control? (Another hissing issue)
[Re: keep_hope_alive]
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bnovak
SD Ralph Wiggum
Registered: 07/08/09
Posts: 53
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yeah I still have the old one, and no, it doesn't re-produce the same issue, so it definently has something to do with the new HU.
I ordered a PAC OEM so I'll try adjusting the gain's and see if it helps.
I'll keep you posted.
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#1693798 - 08/15/09 06:25 AM
Re: Line Level EQ / Gain control? (Another hissing issue)
[Re: bnovak]
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keep_hope_alive
in another life, i'm a serial killer
SD I Power Bombed the Undertaker
Registered: 04/24/07
Posts: 13370
Loc: Quad Cities, IL
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regardless, you should use the PAC device when interfacing with a factory amp. good luck!
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#1698160 - 08/26/09 09:35 AM
Re: Line Level EQ / Gain control? (Another hissing issue)
[Re: keep_hope_alive]
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bnovak
SD Ralph Wiggum
Registered: 07/08/09
Posts: 53
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Well, now it gets interesting.
I installed the PAC OEM module the other night and noticed things are a little weird. (and of course, I didn't check this BEFORE I installed it, so I don't know if it was happening before.)
Now, I only have the hissing on the front channels. The PAC helped a little, but I've got it gained down almost as far as it goes. The weird part is that the rears have no hissing whatsoever, at any gain adjusted level. Full on, full off, anywhere in between it doesn't matter.
I didn't think it was possible, but the only thing I can think of is that my front components are not compatible  with the factory amp, but the back speakers (coaxial 6x8) are since there's no hissing from them? the measured impedance is pretty darn close on both sets of speakers (3.86 front versus 3.89 rear) so I can't see 3/100's making the amp that fussy....nor have I ever heard or seen this type of issue before, but I guess it could be possible. I'll havta go and re-measure the impedance of the factory speakers I took out of the doors.
oh well. Guess it's a good enough excuse to rip the factory amps out and go with a 5 channel
any other ideas?
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#1698186 - 08/26/09 10:36 AM
Re: Line Level EQ / Gain control? (Another hissing issue)
[Re: bnovak]
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keep_hope_alive
in another life, i'm a serial killer
SD I Power Bombed the Undertaker
Registered: 04/24/07
Posts: 13370
Loc: Quad Cities, IL
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swap the signal wires going into the factory amp. swap front with rear. see if the hissing moves.
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#1698600 - 08/27/09 09:40 AM
Re: Line Level EQ / Gain control? (Another hissing issue)
[Re: keep_hope_alive]
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bnovak
SD Ralph Wiggum
Registered: 07/08/09
Posts: 53
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yep, that's on the list of things to try. I'm also going to try and wire the components straight to the head unit and see if it still persists.
it wouldn't be fun if it worked the first time, right? 
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