high-pitch squeal
 

my car has a basic 4ch factory audio system,
quite some time ago I tapped in a line-out converter behind the radio (I cut the rear speaker leads and hooked the loc to those leads.)
I then ran a set of rca cables to a sub in the trunk with a dedicated amp mounted to the sub box.
That has worked fine, great bass, other than the fact of not having the rear speakers hooked up for a while now.

Recently, I installed a second amp in the trunk to drive the rear speakers, I ran a set of rca''s from the output of the sub amp over to the new amp.
When I fired it all up there is an extremely high pitch squeal coming out of the rear speakers. The audio works but is almost drowned out by the high pitch tone. sort of sounds like feedback but is a steady tone.

I disconnected the rca's that were feeding the sub amp and ran them straight into the new amp (I thought there was some kind of crap being introduced by daisy-chaining the signal via the sub amp),
but not so, it still squealed...

the high-pitch squeal is still there even with the sub amp bypassed altogether.

I thought maybe there is something wrong with the new amp, so I got my hands on a couple of different amps, tried each one with the same results. so I don't think it is the amp.

so it must be something in the signal coming from the radio thru the line-out converter.
hmmm...a line-out converter could add a high pitch squeal?? weird.....

the bass amp works great, I guess it just filters out all the high stuff.

but what could cause such a horrendous sound for the rest of the signal??

how can I fix this problem?

Thanks

The high pitch squeal is oscillation. You have a bad LOC, or a ground loop problem, causing the LOC to oscillate.

Good luck with that. :)

the loc has a fifth wire on it that I did not hookup.
it looked like a separate ground wire to me, the car-audio shop said it did not need to be hooked up to anything.
hmmm...maybe thats cuz I was just doing the sub hookups back then.
is anyone familiar with a separate ground cable on a loc??
could it help fix my problem?

or should I just get a new loc?

thanks!

that IS a ground, try hookin it up, I hope it works 4 u

yep, that was it.
once I connected the ground it was quite a bit better, I also had to turn down the gain on the amp to its lowest level.
That got rid of 99% of the high pitch squeal.
I'm pretty sure I can still hear something when the radio is turned down all the way, maybe my ears are gimped now, maybe dogs can hear it, I dunno, but with the volume up it all sounds great now.

Thanks!

add a neg to the deck and a neg to the rca"s and at your amps have them go to the same place for the neg

Perhaps the sound you're still hearing is induced by the alternator ? Check if the pitch changes as you rev your engine. If that's the case, make sure your signal wire and power wire are seperated as much as possible.

I have that problem in my car right now, but I'm too lazy to fix it, so I just listen to music loud enough to drown it out. (damn stock power wire that runs the full length / width of the trunk.

no it doesn't seem to be alternator related. it is steady regardless of rpm.