line drivers, preamps, filters, good or bad?

I seen an old thread about the use of pre amps & filters that turned into a huge "coke vs pepsi" type debate.  But it never answered the original question. 

I had a Punch mono with 2 10", and an infinty reference 4 channel hooked to a factory stereo, loud, but poor SQ. When i bought a JVC KWXG/700 to replace the stock deck, (at 2.5 volts preamp for the rca cables). There was simply hardly any power for the amps and a loud buzzing. I had to turn the gains all the way up to get "ok-ish" volume.  When i asked the local stereo shop, he sold me a "line driver and some inline patch cable filters". Though these products did fix the volume & buzzing problems, i could only wonder at what expense to SQ?  Was there something i missed during the install? i retraced my steps countless times, replaced & moved patch cables etc.... Ive never had to use these products before..... why now? 

Car audio is better than it used to be, but there's still a wide variety of specs and not so much conforming to standards.

Matching various components piece by piece by input impedence, sensitivy and noise isnt easy. You can't always take the specs at face value either.

Depending on the output specs of one unit and the inputs specs of another, a line driver (amplifier\filter) is required.

They arent evil and if you require one to begin with, you're going to hear anything that says "wow that Class-A system sounds like $#@! now".

I know just enough to be dangerous. VERY dangerous.

Those Infinity amps may have a voltage input switch, if so are they on the right setting? and simply sorry for asking power on one side of the vehicle at wire,rcas, remote on the other, good clean ground(no paint), are the rcas covered behind the deck at not touching medal?Chadillac

Thanks for the advice guys.

 I thought the infinity must of had some switch like that but couldnt find anything. The Rockford mono also suffered the same decrease in input power though.... So i thought either 2.5 volts or JVC quality must be the reason??

extra equipment like EQ's and line drivers can be very prone to noise. any brand can get noise but low end brands are almost a sure thing. ALL GROUNDS need to be good ones on this type of equipment. line drivers are very useful when it comes to sound quality or SPL. they allow you to turn your amp's gain down and shouldn't be used like a volume booster to make your system extra loud because this introduces extra distortion that you amp then must process plus adding its own small amount of distortion before it even gets to the speakers. if you keep your line driver turned up then, yeah, you will have hiss in your system. every piece of electronics has a small amount of hiss in the signal. when you add a line driver all it does is amplify that hiss. the good thing is that you should only hear that hiss if you have the LD turned way up AND your amp turned way up plus whatever else you have installed in-line with the RCA's. i use a JVC KD-AVX77 with a kenwood 9-band eq and a Cache active crossover with line driver and i have no noise or hiss. only when i turn my radio up way past listening level can you hear the hiss in my system. everything has its own solid ground to bare metal and all of my middle of the line RCAs avoid crossing anything that carries more that 10A of current. the RCA are also as short as possible so i dont have extra rolled up under the carpet. so, the answer to your question about the effectiveness of line drivers is yes they do help and they have their own uses. they only cause problems when they aren't used or installed the right way. and you should never need to use a filter if your stuff is installed the right way.

Thanks for the reply soundnsecurity, originaly i did have the rca's running along both power cables to the back on each side of the vehicle.  The buzz was horrible, i moved the rca's down the middle and it was much better. Unfortunatley the low signal to the amps was unchanged. Since im thinking on upgrading the deck ive been reading the spec's on many of them to see most are in the 2-2.5 volt preamp range. so 2.5 shouldnt be a bad level for an amp, right? All of my equipment was made from the same time period so i know aged with new isnt the problem.

Do those inline filters reduce sound quality?

im not exactly sure about the filters reducing sound quality but i would imagine it filters out some frequencies in the music itself so i would say yes but most people never notice it at all. a 2.5 volt output isn't bad. it usually matches up with the amp's gain at 1/3 to 1/2 of the way up. if you keep looking there are a few decks out there that give you 4 to 5 volts on the RCA output the JVC KD-R900 is one of them.

Sounds like a bad ground at the deck and you've found slight improvements by moving other things around.  You shouldn't need a line driver to get the signal back 12 feet from the deck to the amp.

https://www.the12volt.com/installbay/forum_posts.asp?tid=48376&KW=DYohn&tpn=2

https://www.the12volt.com/installbay/forum_posts.asp?tid=82401

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Never thought about double checking the ground on the deck. I just "assumed" it was good because i used the original ground wire from the stock deck. Might have to dig back there and have a look see. Thanks Steve