Just finished the install on my amp...this post for more info....here is my problem...

I have a Kenwood Ecelon KDC-X689 head unit with a MTX Thunder 895 5 channel amp. When I ran the speaker wire I tapped into the stock wiring from the amp to the speakers by the head unit because the doors of my 05 F150 have an actual large plug instead of just a rubber boot and I did not want to drill holes in the doors.

I noticed after the install that I can hear a slight hissing sound from the speakers. It gets a little louder if I turn the gain on the amp up, but engine speed and all that have no effect. The head unit has settings for CD, Tuner, Aux and Stand-By. I hear the hissing on everything except for the Stand-By mode.

I am thinking that it is from the head unit and not the amp since the noise goes away when I switch it to Stand-By. I figuire if it was coming from the amp I would hear it all the time the amp was powered. Could it be the ground on the head unit? It is grounded through the factory wiring with an adapter. Also, if it makes a difference I have the head unit internal amp shut off and am using shielded RCA's from KnuKonceptz and they are run about 3 feet away from the amp power line.

It could also be a gain setting issue I am new to all of this. According to the amp directions I set the gain my playing a song with the head unit set to 3/5 full volume. It says to turn the gain up until you hear distortion, but I turned it up all the way and did not hear anything I thought was distortion. Maybe I was wrong. Anyway I backed the gain off a little just to be safe.


Thanks!

Dave

 

By Stand by I'm guessing that it is like mute. If it is mute then the HU might be cutting the rca signal from the amp to the speakers, thus it might be an amp problem. My guess would be a bad ground. Is the ground on bare metal? How long is your ground wire? Also, I see that those RCA patch cables are pretty long. You have 5 volt pre amp outs put but maybe by the time the signal gets to the amp its distorted a bit with "hissing" noise.

 

The Stand-by actually shuts the amp off. Upon further looking I decided to check the amp alone by unhooking any incoming wires from the head unit (RCA's and remote turn on.) I powered the amp up to turn on by jumping the remote from a different source (the amp power lead) and disconnect the RCA's and the noise is there, so it is not coming from the head unit. It is in the amp. The ground is on bare metal and is about 3 feet long. I tune the amp gain all the way up and really hear it. Is it a ground issue or just the amp quality? If it is the amp, how can I best reduce it?

Thanks!

Dave

 

It sounds like a ground problem to me as well. Try shortening the length of your ground wire.

 

What length should it be? I have heard too long is bad and I have also heard too short is bad.

Dave

 

i've heard 5-8 inches is the number. I keep mine at 8-9" if possible. You could also try some bigger guage wire. Try a 2 or 4 guage wire if the amp will accept it.

 

My first thought would be the gain being set too high. That 3/5 should actually be 3/4. At least, every thing I have ever seen about setting says 3/4. At 3/5, the volume would be at a lower volume than at 3/4. You might try that. Also, if you turn the gains down to get rid of the hiss, do you have acceptable volume level? If so, then that is the answer.

Hiss is a very difficult problem but, improperly set gains can really cause alot of problems with hissing.

 

I agree that it could be the gains. I would definately recheck them and adjust. It should be at 3/4 volume level. If you could have someone in back adjusting the gains as you sit up front listening for the distortion/hiss. You could also recheck the ground. I have my amp located in roughly the same spot and have my amp grounded to a bolt that is on the floor just below where the amp is.

 

That 3/5 was a typo. It should have been 3/4. I turned the gain down until the hiss was gone and the volume is "ok." I guess I will try the ground on maybe the seatbelt bolt and shorten the ground cable. I think it is is related to the gain though, since the only way it changes is through turning the gain up. Wouldn't a bad ground cause something like static, or alternator whine?

I am still trying to figuire out what "clipping" sounds like. Anyone have a sound clip of it or can explain it so I understand. I have yet to find a good explanation of clipping, other than see what a clipped sound wave looks like and I do not have an osciliscope t see that.

Thanks!
Dave

 

Check this out for more info on clipping: http://www.bcae1.com/2ltlpwr.htm

You should use a DMM to set your gains properly (if you dont have a Oscope). I would still shorten the ground cable and make sure you have a good connection. Do you have a "pop" when your amp turns on/off? The only other thing I can guess if you still have the hiss after setting the gains and fixing your ground wire is that the mosfets in the amp are bad.

 

No pop when I shut off the amp. I saw a tutorial on how to set the amp with a DMM somewhere, but cannot remember where I saw it. Could you point in the direction to set the gain with a DMM?

Thanks!
Dave

 

Email me for it. brypink@***.net

 

sent it off. Will using an Ipod with an indepenant volume control on it have much effect on the volt's I am reading?

Dave

 

I wouldn't think so. I wouldn't have it connected while setting the gain. Sorry, I haven't dabbled with an iPod yet.

 

i never used the rca's your using but even though they say there shielded they may well be a bad set or just not shealded good enough...i would try using monster cable rca's....from my experiance it wouldnt be your gain or your ground causing the problom...but i have come across rca's causing nose...