# PLEASE HELP!: Subwoofer cutting out - amp still stays on - voltage still good



## jooonnn

Hey there guys, I've been helping my friend install a Alpine Type R 10" and MRP-M500 amp into his 2010 Scion XB with the premium alpine head unit upgrade. 

We wired with a 4 gauge kit, decent Rockford Fosgate wire, brand new RCAs from under the hood to the back of the car. Subwoofer is in a sealed box, dual 4 ohm voice coils wired in parallel for 2ohm load.

For some reason, the subwoofer cuts in and out anytime the volume is around 36 or higher. The head unit goes up to about 60, the bass eq is set to 0 (goes from -24 to +6). The gains are set very low, bass boost off on amp. Messing with gains provides no difference either. Ground is terminated with a nice ground terminal black at the spare tire wheel well (flat surface) sanded down. Subwoofer plays and sounds good at less than 36 volume. We tried the subwoofer in my car and it does the same problem. We replaced the speaker wire and reset the jumpers, problem still exists. We shortened the ground wire, then tested continuity from the ground block to the amp, and the amp + and - terminals, all showing continuity. Voltage stays at an almost constant 13.8 with car cranked, and 12.2 without. We then bought a new amp, thinking it was the amp and the same problem still existed. The amp ALWAYS stays on (the light). When car is not cranked, the blue alpine led does "dim" to the bass hits though.

Things we did notice, when we shortened the ground, it allowed us to go a little smidge louder before cutoff. Resistance between the ground terminal and the amp is < .5 ohms if anything. Also we know that when the car is driving with higher rpms it can not cut out as much, but still cuts out. It also cuts out at lower volumes when idle like at stop lights. 

Any help would be greatly appreciated. We have been googling all day trying to figure this out. It always seems to be a grounding issue from what we've read.


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## Abaddon

Have you tried moving the grounding point?

Have you measured the resistance from your grounding point back to the negative terminal of the battery?


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## jooonnn

Abaddon said:


> Have you tried moving the grounding point?
> 
> Have you measured the resistance from your grounding point back to the negative terminal of the battery?


I've moved it once, essentially from one part of the spare wheel well to another, but I have not measured resistance from the well to the battery. What is the best way to do so? I don't think i have a 15ft long test lead


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## PorkCereal

Did you shave off the paint to get bare metal? If the amps are always staying on then thats a remote issue which might cause them to over heat and go into protect. See how hot they are getting when they shut off.


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## jooonnn

PorkCereal said:


> Did you shave off the paint to get bare metal? If the amps are always staying on then thats a remote issue which might cause them to over heat and go into protect. See how hot they are getting when they shut off.


It doesn't get hot at all, the subwoofer shuts off when volume is above 36, and when u drop it back down it takes it a few seconds to kick back in, yet still the amp always stays on.


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## PorkCereal

Wonder if the headunit is putting out a voltage the amp doesnt read. Try turning the gain all the way up see what that does.


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## Oliver

The amp is protecting itself without using more expensive means = lights and circuits,etc..,

SOLUTION = get a bigger amp


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## jooonnn

a$$hole said:


> The amp is protecting itself without using more expensive means = lights and circuits,etc..,
> 
> SOLUTION = get a bigger amp


Maybe this should be in the dumb answer thread.


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## jooonnn

Updates for today:

Battery ground was upgraded, apparently the factory just bolts it directly on painted metal, so we sanded that down.

Ground for amp was moved to another place; continuity and resistance tested GOOD.

RCA's were swapped with new ones.

Subwoofer was tested on another amp in a different car, sounds great.

Amp was tested in another car, sounds great.

The dimming of the alpine LED stopped, glows nice and bright after the battery ground was upgraded.

Subwoofer STILL cuts at the 38 range of volume. 

Called a reputable shop owner with a Scion XB same model and he said that it could be signal issue. 

Keep in mind this is only a 500w RMS (probably reaches no where near that) amp. Nothing in the car is dimming either. 

Connected RCA's to an ipod connected to the amp, and the subwoofer does not cut at full tilt on the ipod. 

My guess is that the headunit is sending it a bad signal, causing the amp to stop playing the subwoofer to protect it.


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## samdoan

I'm gonna subscribe to this thread.

I have almost the same exact problem. My sub amp will stop playing when I turn the volume up. The amp's power light stays lit and my 4 channel amp running off the same distribution block stays on.

I'm running an MRP-M350 and you're running an MRP-M500. Different generation but both Alpine and not too big of differences between the two.

I've been unable to find a fix and it's been annoying the hell out of me.


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## TREETOP

jooonnn said:


> ...brand new RCAs from under the hood to the back of the car...


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## jooonnn

you know what i meant


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## thebeaushow

I realize this is a very old thread but I am having the EXACT same issue. Did you ever find a solution? I've tried new rcas, new head unit, different subs, amps, everything and the sub still stops playing while then amp is on.


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## jooonnn

New headunit fixed everything for the scion


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## deesz

some cars ie. honda, acura, bmw, gm vehicles, etc. have a mic for noise cancellation or speed adjust. essentially when you turn up the volume it will cut out bass freq. the solution is to disconnect the mic on some cars and others you can just go in and change the settings on the radio. most people dont notice it however when you add subs it will cut out the sub when you turn it up. just food for thought for those of you having this issue.


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## Billlls

jooonnn said:


> New headunit fixed everything for the scion


 mine is doing the same thing I have 3 15inch fosgate and 2 500.1 amps


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## Billlls

jooonnn said:


> New headunit fixed everything for the scion


 mine is doing the same thing I have 3 15inch fosgate and 2 500.1 amps


deesz said:


> some cars ie. honda, acura, bmw, gm vehicles, etc. have a mic for noise cancellation or speed adjust. essentially when you turn up the volume it will cut out bass freq. the solution is to disconnect the mic on some cars and others you can just go in and change the settings on the radio. most people dont notice it however when you add subs it will cut out the sub when you turn it up. just food for thought for those of you having this issue.


Would and aftermarket mike do the same thing I have a jvc double din


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## Trinidad_Taz

I’ve been having the same issue. Have a mono and a sub. At high levels the suv cuts certain notes and even adds in some buck sounds. Tried the sub on another amp in a diff ent car worked good. Tried the amp in another car with the sub and it worked good. Changed the ground from a 4 gauge to a 0 gauge and got a big difference! I’m still getting a cut but at higher levels. Next step I’m gonna try is grounding the back of the head unit from an rca jack to a screw on the deck.. if that doesn't work.. 0 gauge the power wire


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## Trinidad_Taz

Been at it all day will leu guys know how it goes


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## Trinidad_Taz

Got the problem fixed ! It was ground wire and power wire insufficient.. 0 gauge from the battery to the splitter box and 4 gauge from the splitter box to the mono block. 0 gauge from the mono to the grounding point. And WaLA it works perfectly


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## casper2219

If I just turn the car on and not start it the bass will play until I start it. All the while it was working before this started to happen. Can you help me please


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