Alright, I hooked up a JL 12w1 8ohm sub to my mtx 302 rated for around 300 watts at 4ohms at 12v. It sounded ok for a little while. It's starting to distort and send random signals through to the sub - random booms coming out of no where.

The ground is good, the power cable is good, signal is from a sub out on an eclipse avn5510 with the wires run down the door channel and away from the power cables, remote wire is in place.

This got me thinking...an 8 ohm speaker on a 4 ohm amp should produce less load and be easier on the amp. It should just cut my power in half so I'm sending 150 RMS instead of 300 RMS - fine by me for a single 12.

But, I'm getting distortion. The amp has a built in eq and hp/lp filter. From what I've heard, cross overs are set for a certain impedence and will not sound right and can cause issues if you attempt to run different impedences through them. Think this could be causing my distortion?

 

That is pretty much on a passive crossover (say a crossover for a set of components) where if you change the impedence of the driver, the crossover point will also change. That is why a passive xover has to be built around the drivers; cant have one and just go throw and random drivers on it unless you do some homwork really.
That most likely is not your problem.

When you say "sounded ok for a little while" what do you call a little while? A week or two, a day, a couple minutes??

How are your gains set on the amp?

 

It sounded okay on the first day...it was on for maybe an hour at low volume. The second day I thought I noticed it a little but I hadn't yet turned the volume up much (girlfriend likes conversation, not music). The third day I made a road trip by myself and cranked it up a bit. The distortion became very audible. At one point I pulled into a gas station and killed the motor and the sound continued with the iginition in ACC - so I don't think it's noise picked up in the RCA cables. I also double checked my ground and power source. Power is a 5 gauge runing from the battery post down, under, and back up through the jack plate. Ground goes right to one of the jack plate bolts and is making good contact.

The gain is at about 1/3, eq is in the middle. This is where I had it set in my last application. Last time I had two of these same speakers instead of just one and I wired them down to 4 ohms and ran the amp bridged.

The sound is most often heard after a loud bass hit. It's normally a rumble followed by some thumps and then stops. It seems to occur more frequently with volume. The later occuring thumps sound fairly uniform and rythmic - made me think it was a capacitor in a cross over charging and discharging through the driver. Once the sound starts pressing mute or turning down the volume has no effect, the sound continues for a couple seconds.

 

Your positive you have a good ground?? Might want to try a different place and make sure you have a real good tight connection to shiny metal.

Im thinking its NOT something wtih the sub, but just to rule it out better, if you have a multimeter try reading the impedence of the sub (with it unhooked from the amp). It should be somewhere around 8 ohm, give or take one ohm or so.

Im guessing something with the amp or the install...

 

+1
Seatbelt bolts are notorious for intermittent grounds. Like Bartak said try another place, scrape off some paint and ground there.

 

Right now its grounded to one of the bolts that used to hold the jack in. It looked like a good connection and I scraped it up a bit but I'll take another look at it tonight and use a file or wirebrush to really clean it up.

 

Same thing. Put on body metal.

 

Alright, took the bolt out, took a file to the bottom of the bolt head and to the body where the bolt goes through so I have lots of nice shiney metal making contact.

The truck was running (girlfriend was cold and wanted the heater) and I plugged the ground back in to the amp after reattaching it to the truck. The amp fired right up but it still distorted so I backed the gain all the way down and tried to retune the amp. With the gain all the way down the distortion goes away (so does the music). But by the time the gain is at about 1/2 you can hear it again. I backed it down to 1/3 and left it alone. It sounded fine.

We pull out and run some errands. When we leave the store I fired the truck up. Immediately there's a "thump (1/2 sec pause) thump (1/2 sec pause) thump etc......."

Is it possible for there to be some sort of surge when I start the truck? My remote lead is coming from the ACC lead on the back of the stereo, input is RCA cables from the sub-out on the Eclipse AVN5510. Power is straight from the battery.

I'm afraid to go buy a new amp just to have the same issue

 

Alright, checked the voltage on the remote, and power source both with car on and off. Power's good. Sub has the correct impedence. Tried hooking up the sub to both channels one at a time instead of bridged. Same issue happens. The amp is shot:-(

What do you guys think of MA audio? Sonicelectronix has them on clearence.

 

If all your connections are good and proper, sub checks out ok, signal from the HU is good....you may have an internal amp problem then.
What kind of amp are you running?

 

MTX 302. It's a 2 channel amp that they made a little while ago.

 

K. Was just wondering if it may have been an amp that is known for some problems or not. I really dont know much about those amps.

Do you know anyone with an amp that you could swap in there to test?
If that swapped amp works fine then you know you have an issue with your amp, or if it still does it then you have a problem elsewhere still....

Always nice to do something like that just to be certain, before you throw down the cash for a new piece of equipment when your old one worked....

 

I was looking around at the mess of old car audio that I have in the basement and realized that I do have a Pioneer that's good for 150w bridged at 4 ohms. I'm hooking it up tomorrow to test the system.

I was lookin on line and I found a bunch of MA amps on clearence at sonicelectronix.com. What do you think about MA amps? Keep in mind I'm not really looking for a competition solution. It's to power a single 12" at 8 ohms. I've never heard of them

 

Well I just went out to the parking garage at lunch and hooked up the pioneer. It worked just fine. I guess the old MTX has finally had it. Grrrr...I guess I have to buy a new amp now

 

I think they make good door stops.

I would keep looking...if your going to spend the money, spend it on something that has some quality and will last a while.
MA doesnt fit that bill in my opinion.