Amp in protect mode while engine running

[UrbanRedneckKid]

This is driving me crazy. First off it's a MTX 720X 210w amp, powering a 10" Kicker sub, from a Pioneer DEH4800 headunit. Everything plays great with the engine off, as loud as you want it, no problems till the battery dies. BUT, while the engine is running the sub plays for like 30 seconds and then cuts out and the amp goes into protect mode, then kicks on off on off... . My power wire(8G) is hooked up to the battery side of the starter solenoid and I have a good ground(8G) right into the floor. Also I have a 25 CFM cooling fan on the amp. I can't find anything wrong. Any ideas???

 

[Black'03LevelII]

first off I would rewire the power directly to the positive post of the battery (with a fuse of course) secondly turn your gain adjustment on the amp down. Gain only needs to be set right around 1/2 to 2/3 (not the max)

what is happening is your amp is trying to produce to much power and is clipping. I've seen this exact same problem countless times, and simply turning the gain down has fixed every single time.

hope this help and keep jammin the tunes!

 

[Pistons23]

ive seen something similar with a friends setup. but his wouldnt cut out as fast as yours. his problem was that one of the leads to the speaker broke free and was causing a short. he soldered it back and it works perfect now. just something else to look at besides the gain option mentioned above.

 

[UrbanRedneckKid]

BUT why does it only do it when the engine is running? Also my settings are: EQ Bass: 0 of 6, Bass Boost 0 of 6, Loud is on Low, and the amp gain is 1/4 way up.

While the engine ISN'T running- you can crank all the settings to the max, and it will play all day without cutting out.(Distorted to hell of course) but it play with out skipping a beat(pun intended)

I will see tomarrow about going straight off the battery

 

[Psychopete]

I will see tomarrow about going straight off the battery

This is sort of the first thing I thought of. I've never heard of anyone running their power wire from there .

You might also test the voltage from the alternator as well with a volt meter. Should be between 13.5-14.6ish with the car on.

I had an alternator in my truck that went bad, it read 16 volts with nothing on at idle, and 12 with everything on at idle. This wasn't good. Replaced w/ a new one and it read 14v no matter what.

Pete

 

[AllanD]

It's likely that you have a problem with your alernator.

Get (borrow) a Digital multimeter and set it to AC-volts range and measure the AC volts at the point where the amp is getting it's power.

It's likely that you have a shorted diode in the rectifier section fo your alternator.

This means that "spikes" of AC is leaking past the diodes and this can be seen
with a digital multimeter.

If there is a bad diode you'll see anywhere from 0.2V to 1volt (or more)
"leaking" past the diode.

that can drive self-protection circuits nuts.

If that is the case you need a new alternator.

AD

 

[UrbanRedneckKid]

There's the answer I was looking for, Thanks AllanD
I'll definately check that out tomarrow.

Any other suggestions are still gladly welcomed.

 

[UrbanRedneckKid]

So I checked my alternator, it's working perfectly.

Also I finally moved my power wire straight to the battery, It didn't change a thing and it looks like crap.

Anybody think I might just have a defective amp??? I only have a week and a half before my 30 day warrantee is up. Should I take it back to them? Or maybe I should get a more powerful amp?

Also I was thinking about getting a capacitor. Cause the amp seems like it gets starved of power after hitting a few times. If the hits are more spaced out is doesn't shut off as fast. Then again a 210w amp shouldn't need a cap, right?

 

[Muddycowboy]

i dont think its starving for power i have a 2000w amp and it takes alot of bass to start it.

 

[UrbanRedneckKid]

OK so I said screw this and made an appointment for this sunday to have my piece of $#!t stereo checked out by the professionals. (My Conclusion)Amplifiers don't have wheels so I can't fix 'em.

 

[UrbanRedneckKid]

So I didn't get it checked out on sunday because my fuel pump failed me saturday. But while I was under the truck dropping the tank today I noticed a shiny self-tapping screw poking through the floorboard in a nice rusty hole. I used a hole from one of the rivets that held the jack mount to the floor. It looked like good metal from the top, but not so true underneath. I'm moved the ground over an inch with a new hole, and it works perfect.

The ground was good when I ohmed it out but I guess from the vibration of the engine, it messed it up. Still seems strange to me but oh well it works now.

Thanks again guys for your input, hopefully this thread might put someone else in the right direction, Thanks again. Damn I feel stupid.

 

[AllanD]

Have you load tested your battery?

It's possible that your battery is "weak" and you'd never know...

the permenant magnet starters don't require a whole lot of cranking power
and if your battery was weak the stereo could easily be causing the voltage to drop under load faster than the alternator can react.

the usual best test for that is to see if your headlights "dim" on bass peaks.

I have a shiny new Group 65 battery in my truck AND 135amp alternator
I can jumpstart someone and even their cranking the engine leaves you
unsure if the headlamps dimmed or not... audio equipment isn't in the same league.

AD

 

[UrbanRedneckKid]

Wow, I thought this thread died.

Anyways, I do have a problem. The ground didn't fix the amplifier problem, It just lessened it a little. Just tonight I noticed my voltmeter slowly rise after I started the truck then my lights and the VM needle flicker a little bit, at idle. rev it up and everything is ok. And my autometer voltmeter is hooked right up to the back of the alternator.

Then again, I didn't even check it out yet, so it might just be something stupid, like a loose wire.

 

[UrbanRedneckKid]

Finally Fixed!!!

So... How come nobody mentioned checking the ohm load on the subs?
Apparently a 1 ohm load on a 4 ohm amp, will work at 12.6volts, but not at 14.7 where it's actually doing some work.

The terminals on my sub aren't labeled as to which voice coil they go to and in the midst of guessing My coils were wired in paralelle and wired bridged on the amp, giving me a 1 ohm load. I'm lucky as hell I didn't cook my amp.

Thanks Again Guys

 

[Pistons23]

good job sherlock

i guess we all figured that the wiring was done correctly