More engine noise,

raroberts

I have read the various threads about engine noise, and I learned quit a bit. I have a little but different configuration and would like your expert comments.

I installed a 4-chan Polk amp (c400.4) under the rear seat and 4 new speakers in the stock positions (Ford F250 crew cab). I did not replace the stock head unit.

For each channel, I soldered the signal cables (included in street wires amp wiring kit, 8 gauge power cable) to the stock wires that went to the stock speakers and ran them back to the amp. The amp is switched to use high level input.

I ran speaker wires (18 gauge) from the new speakers back to the amp. There is one speaker and signal wire (left front) running on the same side of the truck as the power cable.

I could not locate the radio on signal wire to wire to the amp, so I used a "hot while ignition/acc on" source for the AMPs "turn on" signal. So the amp is on when the ignition is on, wether the head unit is on or not.

My issue is engine noise.
The noise can be heard when the head unit is on or off (the amp is always on).
The noise does not get louder as volume is increased.

Crutchfield tech support said the noise had to be coming from a speaker wire because the volume of the noise stays constant. Comments?

All the threads I read about this issue focused on the signal/RCA cable as the source of the noise. It makes sense the noise would be amplified according to the volume level if the RCAs were the source of the noise.

I also saw a post that said high level inputs can induce more noise than low level inputs. Would it make sense for me to put a high-level to low-level converter close to the head unit and run low level signal back to the amp?

The gound to the amp is short (2 feet) and goes to an existing ground post on the body. It looks to be a good ground (no paint, heavy stud and bolt (3/8")

Thanks for anything you guys can tell me. I am good at mechanical and logical things, but I am totally ingnorant about electronics.
Randy

neomagus00

simply based on the observation that it doesn't change with volume, i'm inclined to believe crutchfield. you could perhaps move the left front speaker wire to somewhere else? (i ran mine through the console area over to the right speaker, then they shared a path).

the issue with the high-level inputs is noise. the high-levels themselves aren't often the culprit, but instead the noisy already-amped signal from the stock HU. if you can live with it, i'd reccommend an aftermarket headunit, just to be sure on this end (plus, it makes other things like xovering easier, and less noise to boot). thus, adding a converter in the path is likely to just add more noise.

MacLeod

If the noise persists with the head unit OFF then its not coming from the head unit so its coming from your wiring and since youre using speaker level inputs Im betting its coming from that.

I think Neo had the best suggestion. Buy an aftermarket head unit and run RCA's to your amps and I would be willing to bet it would get rid of your noise.

Circuit City has plenty of very good h/u's For $100-150 with free install so there is really no reason not to get one unless youre car's stock h/u is one that has HVAC and other controls in it which the SuperDuty does not.

LittleCar_w/12s

Here's my suggestion:

>>as it is set up, listen for the noise with the setup on. See if the noise changes volume when changing the amp's gain.

Also know that an aftermarket amp will be expecting more speaker-level voltage than stock decks will output. This causes you to need to turn up the gain further, which amplifies noise in the deck output or the lines.

>>Second, I reccomend taking off the speaker-level inputs at the amp, and lying them aside. With the deck off for it's sake, turn the vehicle on and listen for the noise. If it doesn't go away, the problem is in the source power or the speaker wires. While you can't test it with the power disconnected, you can check with only one speaker connected at a time. This can isolate it if it is a speaker-wire problem.

Just to be sure that you are testing the speakers using a clean source, take a cd-player and a headphone-to-RCA adapter cable to use as your amps source.

>>At this point if all the speaker outputs show noise when tested singly, you have a ground or power problem. Another problem may be where the turn-on lead is connected. You can test this by bypassing the power-on to the positive terminal on the amp instead. The power filtering in the amp should keep it clean.

1- check noise -vs- amp gain setting
2- check noise -vs- no signal or external (cd-player/walkman) signal
3- Check speaker leads one at a time
4- check power-on lead and power cables.

I had a terrible noise once, and it turned out to be a cut on the power-on signal wire rubbing paint on the car body. You never know.

Keep us updated.

raroberts

Thanks for the input. This all may be moot for me now.

I was getting an annoying "screaching" noise in my right front speaker during high volume, and from what I could tell it was when the drums in a song were loud. So I was playing the unit pretty loud (about half volume on the head unit) and trying to see if anything was loose in the door, or the noise was coming from the speaker. Then, alll of a sudden the music stopped and left a very loud screeching noise, then popping, then nothing. Long story short, the head (stock factory) unit blew. Before I installed the amp, I would regularly run the unit at 3/4 or higher volume. The amp must be drawing a different enough load from the speakers that the head couldn't handle it. Now I've got a good excuse to get an aftermarket head, with pre-outs.

BTW, before this happened, I dettached all the inputs to the amp one at a time while the engine was running. The engine noise just got a little less with each channel. it went away completely after all the inputs were detached.

I will use good signal leads and run them down the miffle of the car next time. Thanks for all your help!!
Randy

Jstas

BTW, before this happened, I dettached all the inputs to the amp one at a time while the engine was running. The engine noise just got a little less with each channel. it went away completely after all the inputs were detached.

That noise wouldn't be on the speaker side nor through the line level inputs. That whining/humming noise is indicative of a transformer on it's way out. It will pick up all kinds of resonances from the power source. Sorry I didn't see this sooner. You are probably right and the amplifier had a different impedance level that the stock stereo could not handle and it went kablooey!

MacLeod

Well it may not seem like it but it did you a favor. Now youll have to get an aftermarket head unit which youll like about 1000 times better!

raroberts

Thank you for all your help and comments. I got a new Kenwood EZ500 head unit and ran my signal cables down the middle of the truck (which was not easy) and it sounds terrific. The only problem I had was setting all the amp controls. Polk's instructions are very sketchy for a novice. I also bought a Profile amp for the sub, and their instructions were much better. To top it off, the head unit also has equilizer and bypass filter controls, which I left alone. I assume all these controls ought to be done on the amp.

I also got a suprize when I tried to put the back seat back in my truck (F250 crew cab). It wouldn't fit withg the sub box, which Crutchfield said would fit. I ended up trimming away all the interior padding behind the sub and really jammed the box tight against the back wall. The sub sits right against the back seat, but it still sounds good.
Thanks again
Randy

audiobliss

Glad it all worked out for ya!