low grade noise/ground wire or improper amp leveling?
 

hi

i recently had an amp installed and the speakers upgraded at the same time in my '01 F150 supercab. I now have a constant low grade hum with the volume turned all the way down. It doesn't increase when I step on the gas. Is this normal? I noticed that the ground wire is screwed to a metal plate near the floor which is actually part of the seat unit. I thought the grnd wire was supposed to be attached to the floor. Or does this matter?

I also thought that the noise might be coming from improper leveling of the amp? (it's a 4 channel).

I kept the stock head unit, so maybe that's the problem, but I don't have the bucks to replace it.

any ideas that don't require an electrical engineering degree?

thanks!

Try and move the ground-that is a good start.
Also, the ground wire should be the same size gauge as the power wire.
Did you maintain the factory HU ? If so, how did they wire it to the amp. Also, which amp did you get.
You might also, try turning the gain(s) down on your amp.

Is your amp power cable running on the same side of the truck as the outputs from the head unit? They should be on opposite sides of the cab to prevent interference.

hmm... i've looked at the ground wire and it's nowhere near the same gauge as the power cable.. so that would be a start...i'll also try moving it to a different spot...

I'll also try turning down the gain controls a little and see what happens..i'll try that first.

as far as how they wired it from the stock head unit...or if the head outputs are on the same side as the power cable...i don't think i could tell that unless i took off some dash panels..don't want to do that....i have no clue...i don't know how that stuff works...

the amp is a power acoustik farenheit...that could be the problem as well...i know it's not exactly top of the line equipment...i had them locate it under the front passenger seat because that seemed like the logical place...

i'll try a few things as post back...

if it sounds like a guitar amp humming when you touch the plug, inspect your power cable for damaged (scraped or cut) insulation. if you find anything, either splice it -insulating thoroughly- or replace it. If you cannot find any damage, replace the cable with one that has better insulation. You probably want to go with a AWG6 to AWG8 cable anyways.
word.

couldn't find a break in the line, and the plug didn't hum when i touched it.

i turned both of the gain controls down and that seemed to get rid of almost all of the noise. Only problem is, it seemed to affect the volume as well. I have to turn the volume up a lot more to get the sound level I got before. Now, I don't think it's even much more than it was with the stock amp and speakers!

the amp has high and low pass dials on it as well. maybe fooling with those will help. I have both sets of speakers on 'full range' mode right now.

Give us some more info on your setup.
Some cheaper amps by design have noise do to design.
If that isn't the case, the amp may have an internal problem causing the noise.
Also make sure that your RCA lines are not by the computer. They can pickup noise from there as well.

i'm not sure what to tell you all.. i kept the stock head unit... bought a power acoustik farenheit 640Q 4 channel amp (75 rms per channel) and 4 planet audio 5x7 coax speakers.(60 rms). these are plate type speakers.. the tweeter is completely separate and they have a crossover on the back of each..
i know the speakers don't match the power, but i didn't plan to blow my head off with this setup in the first place.. I just wanted a little more volume.. especially on an FM station i listen to which is a little on the weak side where i live.. i'm kind of far away from the source.

I had all of it installed, so i have no idea of the quality.. I did fool with the gain controls again tonight and turned them up a bit.. it helped with the volume.. but of course increased the noise a little.. i guess the next step is to try and move the ground wire.. by the way, the ground is the black wire leading out of the plug in the back of the amp (along with a hell of a lot of other wires from that plug).. seems pretty skimpy... i take it that is the master plug in.. is that the right wire to use for a ground? seems like it would be too small in guage..

hmm.. i'll see if they run by the computer.. good idea..

It sounds like you are using speaker level inputs. It also sounds like the amp may not have been wired properly or the inputs are not of good quality inside the amp. Either/or, but probably both. I would take the truck back to the installer and have it fixed. You should not have this noise. As far as the dif in power, 15 watt is nothing. I typically run my power about 10-15%over the rated for the speakers. My MTX doors are rated for 50, but I am feeding them with 60 without a problem.

As far as the ground, their should be a powerstrip with 3 connections marked +, -, and remote. The + and - here should be the same size. 8ga line for an amp this size. The speaker level plug should have 8 wires I believe (2 for ea speaker).

Hope this helps some.

Couple things....

First off, put those high pass crossovers to use. Try starting around 70hz or about 90hz if you like blarring your stereo.

Second, if that ground wire is a different gauge take your truck back to the installer and tell him to replace it. Check to see that your grounded to bare metal and not paint and that your ground cable is SHORT (<3ft). It could also just be the fact that they used either a Line Out Convertor (LOC) or used the high level inputs (speaker wires) to deliver the signal to the amp. Noise is very common when using high level inputs.

As to the gentleman that recommended checking the power wire for nicks...what is your logic behind this? The insulation on power wire is a simple PVC coating, no shielding. If it grounded out, noise would be the least of his problems ;) .

well... i got most of the noise out by fooling with the gain controls and using the high pass filters.
They did use the speaker level inputs...and the ground wire is one of the wires that comes out of the plug.. looks like the same guage as the others. It was attached to painted metal, so i unscrewed it and took the paint off under it before putting it back. That seemed to help too. There's still a very small amount of noise with the volume off, but it's barely noticeable now..

thanks for all of your suggestions...