# Amp cuts out for a split second at medium-high volumes



## jdunk54nl (Apr 25, 2015)

Here is what I have (all of it is about 2 months old)
Image Dynamics xs-28 tweeters and x65 mids
JL audio tw3 10:
Rockford Fosgate 360.3
Alpine PDR-V75
4 gauge power and ground
14 gauge mid wire and 16 gauge tweeter wire

Here is the issue:
When I have the volume up to just over 50% and higher my speakers will cut out for a split second, turn back on for a split second and repeat until volume is turned down. It increases the cut out frequency the higher the volume. Normally it is fine but the weather has been nice in Phoenix a couple days to drive with the windows down which required a little more volume. Normally I am well below 50% with the windows rolled up as the cab is super quiet.

Here is what I have checked so far:

Impedance on all speakers - Front tweeters were at 4.6 ohms and mids were at 4.4 ohms (measured from wires at amp), sub was at 3.5ohms measured at sub. Should have been at 2 which concerned me so I checked individual voice coils and they were both at about 5.2ohms. I emailed JL about this as the difference between 3.5 and 2 is quite a bit!

Voltages: Mids/Tweeters were set at 17 volts which is about 72 watts for 4 ohms when amp is birth certificate said 116w at 2ohms. Subwoofer was set at 27 volts (for 2 Ohms) or about 380 watts (amp birth certificate said 416 watts at 2ohms) so voltages should be good. This was set using a 0db attenuated tone.

Speakers: I unplugged each speaker individually and saw if the problem remained, it did not matter what or how many speakers were running.

Power: checked dc voltage going in and it was constant 13.6-13.8 volts so not a power issue as far as I can tell. Checked the ground and had .3 ohm resistance back to the battery so ground should be good (it is not attached to a seat belt bolt but to a dedicated grounding terminal with all paint ground/sanded off). Also replaced all fuses to be sure one of them wasn't semi-faulty.

No matter what I do the problem of the sound cutting out is still there. I am leaning towards the amp being bad. I haven't investigated if it is the 360.3 much. I tried plugging my iphone in directly to the rca's of the amp but couldn't get enough output out of the phone to produce high enough volumes. 

Any other suggestions to try or is it time for me to call alpine as I have only had this thing for about 2 months?


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## jnchantler (Apr 11, 2012)

Sounds like a short somewhere. Where did you disconnect the speaker from, at the amp or at the speaker?


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## jwsewell01 (May 28, 2015)

Sounds like a shorted to ground speaker wire to me. At least that what was causing the exact same symptoms I was having with my amp a few months ago. 

When you are disconnecting speakers are you doing it at the amp or at the speaker?


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## jdunk54nl (Apr 25, 2015)

I disconnected all speakers at the amp. I thought it was a short to the speaker as well which I was Hoping to disconnect the right one and figure out which one it was. I was disappointed when no matter which one I disconnected/connected the problem was always there.


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## jnchantler (Apr 11, 2012)

jdunk54nl said:


> I disconnected all speakers at the amp. I thought it was a short to the speaker as well which I was Hoping to disconnect the right one and figure out which one it was. I was disappointed when no matter which one I disconnected/connected the problem was always there.


Did you try disconnecting all of them? Maybe it's on more than one...


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## jdunk54nl (Apr 25, 2015)

Yes I disconnected all of them and reconnected all individually to see if anything helped.


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## jnchantler (Apr 11, 2012)

jdunk54nl said:


> Yes I disconnected all of them and reconnected all individually to see if anything helped.


Just to ask the stupid question, have you looked closely at the terminals? Any possibility anything could be coming in contact with ground? Loose shavings of copper etc?


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## Victor_inox (Apr 27, 2012)

It sounds more like internal amp problem, unless it`s something stupid but your troubleshooting technique seems to be right on money.


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## jdunk54nl (Apr 25, 2015)

I was super careful when connecting the terminals for everything as it is behind my back seat and I didn't want any "stupid" things to be wrong. The wires were stripped and cut to where they were the "perfect" amount to make a good connection but not go too far into the amp. I also made sure that there were no wires touching each other before actually mounting the amp to the amp board and then rechecked everything after it was mounted. I have now re-connected all of the wires to make sure none of that was an issue, mainly through testing everything to figure out the issue. 

I am really thinking it might just be something internally on the amp that, probably during shipping, wiggled slightly loose and is not quite secure enough at higher power to complete the circuit. 

I can't see the 360.3 causing an issue where the sound cuts out as it is really just "passing" the sound through it.


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## Niick (Jun 3, 2015)

So a speakers impedance rating and it's DC resistance are two different things. You CANNOT measure a speakers impedance with a multimeter. It could be that one of the speaker loads connected to the amp is dropping down low enough in impedance, and has a steep enough phase angle at that point to put the amp into protect.

Try this, do you have a iPhone or something like that with a tone generator app? If so, feed the signal from the tone generator into the amplifier, and slowly sweep down in frequency. Use the phone's headphone output, use a headphone to RCA adapter cable, at the amp, unplug the RCA inputs from the deck and plug the phones headphone output in its place.

Make sure the phones volume is turned up loud enough to be in the same range as the deck when the problem occurred. Now, as you sweep down in frequency, and you get to the deep bass range, you'll probably find that at a certain point, the amp turns off, any freq above this point and it will play ok. Ive seen this before many times, it's because speakers electrical resistance changes with frequency, and some speakers drop pretty low below resonance. But it's not just how low the impedance dips, it's the electrical phase angle too that plays a part in how difficult a load a given speaker presents to the amp.

When I get to work tomorrow I'll try to remember to run an impedance sweep of a JL TW3 10, and I'll also check it DC resistance .


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## Victor_inox (Apr 27, 2012)

Niick said:


> So a speakers impedance rating and it's DC resistance are two different things. You CANNOT measure a speakers impedance with a multimeter. It could be that one of the speaker loads connected to the amp is dropping down low enough in impedance, and has a steep enough phase angle at that point to put the amp into protect.
> 
> Try this, do you have a iPhone or something like that with a tone generator app? If so, feed the signal from the tone generator into the amplifier, and slowly sweep down in frequency. Use the phone's headphone output, use a headphone to RCA adapter cable, at the amp, unplug the RCA inputs from the deck and plug the phones headphone output in its place.
> 
> ...


 this or you can measure impedance of each speaker to see if it deeps bellow lowest published frequency using this it`s generates sound frequency and measure impedance dynamically. if speakers in specs that Alpine must be defective triggering protection when it shouldn`t momentarily, then when frequency changed protection released and whole cycle repeat itself.


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## jdunk54nl (Apr 25, 2015)

Hey Niick,
Thanks for clarifying the impedance and DC resistance. You're right AC and DC stuff will be different and I can't compare apples to oranges. I can check the tone generator stuff tomorrow but I tried my iphone playing the same song and couldn't get the volume loud enough with its 1v output without changing the gains on the amp which would be a pain to get to right now . 

My question though is, if I had every speaker removed but one at a time and no matter the speaker I still had the issue. Wouldn't this rule out the individual impedance of the speakers as it didn't matter if I had just the sub or just a single tweeter running. 

But I would love to know the JL DC resistance just to verify my sub is OK. I am imaging it is due to each voice coil having the same value.

Thanks!


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## jdunk54nl (Apr 25, 2015)

Victor, that impedance meter looks cool but for $300 to do this once is something I can't justify. I wish I could but maybe I will just call up a local shop and see if they have something to measure impedance and if so swing over there or try Niick's method tomorrow morning.


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## Victor_inox (Apr 27, 2012)

Good luck!


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## NotInMySpeedos (Apr 8, 2013)

I see you're using the OEM HU.
I had a similar problem because the HU checks for shorts periodically and cuts power if it detects impedance out of range.
The input impedence on your 360.3 is probably high, same as my Bit 10D, up around 10k ohms.
My solution provided by Audison was to connect 100R 10w resistors in parallel with each of the speaker wires connected to the DSP.


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## rabbit (Nov 20, 2014)

I have this same exact problem when I first installed my Clarion VX404 head unit with the stock BMW amplifier. Changed out the amplifier to a Kicker amp and still the same problem so I'm thinking it can't be the amp. The only thing I can think of that I need to fix that I haven't tried yet is re-securing the head unit harness to the car harness. I remember seeing it not fully secured/locked into place but it didn't move so I didn't think it could be a problem. Maybe when turning up the volume, more current or voltage is needed but not being sent through quickly enough because its not fully touching? When I have time, I'm gonna open my dash and check again but you can try that if you're all out of ideas. If you find another fix, post it here and let us know.


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## High Resolution Audio (Sep 12, 2014)

It sounds like you have a bad power and/or ground connection. You can check voltage all day with a digital volt meter. All you need is one or two strands of wire connecting to give you a good voltage reading, because digital volt meters are extremely sensitive. But when you put a load on the circuit, there might not be good enough connection to handle your load. This happened to me years ago. I had a dome light not working. Volt meter said strong voltage. Bulb had continuity. Bulb worked in another light. I was perplexed. Asked the master electrician that I worked for at the time. And he explained to me about digital meters. I searched the wire from end to end for a bad spot and sure enough found a chaffed spot that had green corrosion on it. Re-did that connection and problem solved. Also, your bad connection may be at the head unit and not the Amp.


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## Niick (Jun 3, 2015)

Good morning, so, I must have missed that part about you running the stock H.U. And, ya know what, the last time I had an impedance related-sound-cutting-out-type problem, it was with an aftermarket H.U. with Aux In, so I fed the test signal into that. You're right, I dint think about the level of the phones output possibly not being able to match that of your source unit.

I was trying to think of a way you could use common devices to troubleshoot the problem.......you do have a DMM, yes? Let's see, sometimes, the problem with cheaper DMMs (and even some costlier ones) is that they don't react fast enough, they're reading is really a type of averager, because the time that it takes for a change in voltage to cause a change in the displayed reading can be to long, masking any voltage dropouts that might occur. Not saying for sure that this is what's happening with your meter, but it's something to keep in mind. 

So, what I would try next is rig up a way to be able to test the AC voltage of every input and output, starting with the output that drives the speakers, and work your way backwards thru each device in the signal chain. Eventually, you'll get to some point in the signal chain where your AC voltage is suddenly dropping out to some disproportionally smaller value, exactly in time with the audible sound of the music cutting out. Once you've discovered where in the signal chain this is occurring, then you'll know what component to attribute it to. 

For me, that would be step 1. My apologies if I've simply restated what others have suggested. Getting ready for work now, will try to test that JL sub ASAP, also, good news to those wanting to be able to test impedance. Room EQ Wizard. I made the impedance jig as described in the HELP files for version 5.1 I think, and it works AWESOMELY. It's mainly the only thing I use REW for at work. 

Let me say it again, REW's impedance measurement function WORKS BRILLIANTLY. And it's free.


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## Niick (Jun 3, 2015)

Hey bro, ok I'm here at work, I have in my hands a JL TW3 10'dual 4 ohm woofer, that's the one you want to see correct?


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## Niick (Jun 3, 2015)

Ok, here is VC #1


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## Niick (Jun 3, 2015)

Here is VC #2


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## Niick (Jun 3, 2015)

Here is both VC in parallel


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## Niick (Jun 3, 2015)

I get 2.2 ohms DC resistance with the coils in parallel, taking into account the resistance of my meter leads. I DONT currently have the greatest DMM in the world, however. 

When measuring low resistances like speaker voice coils, it's pretty important to subtract the lead resistance from the reading. Old school analog meters had a "zero" function on the ohm scale, and some of the nicer DMMs have a "Rel" (relative) button, that accomplishes this same thing


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## Niick (Jun 3, 2015)

Just for the hell of it, here's the coils in series, in series I get about 9.0 ohms DC resistance, or 8.9 or so


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## jdunk54nl (Apr 25, 2015)

Niick, Thanks for all of that info! How did you hook everything up to do impedance with REW? I can look this up later if you don't feel like explaining it.

When I measured DC resistance I got 3.5 ohms in parallel then each voice coil measured separately was roughly 5.2 ohms. I took into account the internal resistance of my DMM and subtracted that to get those numbers. It seems like the sub could be a little off but I would like to measure the impedance using REW to make sure. 

That shouldn't impact my sound cutting out as I eliminated the sub in the chain and it still happened. I am going to re-do all of my tests tonight after work and replace the fuses again to be on the safe side that they aren't the reason. One step at a time of course to make sure I can actually locate the reason!

I remembered as I was driving in to work that the 360.3 has aux in, I am going to eliminate the head unit tonight using that and my iphone with a frequency generator to be able to reproduce the levels I need to check to see if the headunit is the issue and check the speakers and the amp cutting out.

If none of that fixes anything I am going to try to find a reasonably priced shop in phoenix to test everything or just call alpine to have the amp replaced. I might do the amp first to save the cost of testing everything at a shop.


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## Niick (Jun 3, 2015)

So, in the next pic is this circuit, wrapped in heat shrink


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## Niick (Jun 3, 2015)

Here's a pic of how I have it implemented in my measurement setup, that coil of wire is the leads, that lump of heat shrinked circuitry with the two 1/4 inch TRS connectors plugged into the back of the interface is the actual circuitry.


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## jdunk54nl (Apr 25, 2015)

Testing Round 2:

Changed the inline fuse and holder near the battery, changed the fuse in the distribution block (all my fuses were bought together so I actually went out and bought brand new ones hoping I just had a bad batch of fuses), unplugged all speakers again just to make sure none of that was causing it.

Attempted to hook my iphone and computer up to produce levels equilvalent to the HU but couldn't get there (only about 30-40% HU volume at max iphone/computer volume). 

Hooked computer up through HU Aux in and Iphone up through the usb port, this would produce the results at lower HU volumes compared to radio which makes sense as radio is almost always quieter than other formats. 

Tried the slow sine wave sweep using REW via HU aux in and computer and Frequency generator on my phone through HU usb. Both had the same result that would cause cut out throughout the entire frequency range, there wasn't really any spot where the sound wouldn't cut out.

I did turn the back speakers on which are powered only by HU and when the front/sub would cut out the back speakers were working fine.

So all in all, pretty much everything you guys suggested to check didn't make a difference. 

I am going to contact pac stereo and possibly alpine depending on what pac says to get this amp replaced. 

My other choice is talking to one of the arizona chain audio stores is that they will test everything for like $75 but when I went in there to buy fuses they said I probably need another battery so I don't know if I trust them when the amp is only putting out 700 watts at max volume and I haven't had any issues with headlight dimming or anything like that.


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## Niick (Jun 3, 2015)

Seems like you got yourself a real doozie there bro! I gotta get ready for bed, gotta go to work tomorrow, I'll be interested to see what you come up with. Keep us posted, if I can think of anything else, I'll post it too. Good luck


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## cajunner (Apr 13, 2007)

I'd say it's the OEM deck not being attenuated enough at the 360.3's inputs, causing overload and temporary muting by the processor...


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## NotInMySpeedos (Apr 8, 2013)

jdunk54nl said:


> Testing Round 2:
> 
> I did turn the back speakers on which are powered only by HU and when the front/sub would cut out the back speakers were working fine.


Exactly what happened in my set up.
Give the resistors a try.


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## jdunk54nl (Apr 25, 2015)

I'll give the resistors a try, although I don't know when I will be able to do that as that means tearing out my seats to get to the connections. Once I do that I will let you guys know.


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## jdunk54nl (Apr 25, 2015)

Called RF tech support today and he had some insights. First one was resistors aren't needed for the basic stock stereo or silverados, mainly for Ford trucks and GM trucks with bose or other stereos that have stand alone amps and aren't powered by the HU. 

What he did suggest was that the 360.3 can output 8v rms yet the alpine input is rated from .2-4v. I set my gains for the amp output based on other threads that said to basically ignore that if you set your outputs correctly. The guy said to lower the outputs on the 360.3 to where it is only putting out 4v max and increase the outputs on the amp to get back to the same volume. He suggested I might just be driving the amp's inputs too hard to where it wasn't built for that much. 

I am kind of shocked that alpine only puts (even on their best) 4v max input when most of the other higher end amps have higher. 

Gonna try this tonight and see if it works


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## jdunk54nl (Apr 25, 2015)

So I think I fixed it today.

Checked the RCA out voltage from the 360.3 and the midbass level was at 5.1 volts at the volume that it started cutting out. Changed the 360.3 back to no tune, lowered the output voltage by the level control in the 360.3 to get it around 3.8 volts out. Reset the gains on the amp and cranked the volume and listened for about 20 minutes with a mix of songs to NO CUT OUTS! Went back to my preset tune on the 360.3 and still no cut outs but the tune doesn't sound the same  all that time spent tuning to have to re-tune again. Aww well just more time with REW and tuning to get better at it and get an even better tune!

It shocks me that when I originally was looking up if I needed to worry about adjusting the 360.3 settings to output less than 4volts that everyone said no, just level set everything and you are fine. Maybe that used to be the case but now with newer amps it isn't anymore.....I don't know, but my issue is hopefully solved.

THANKS FOR ALL THE HELP DIY COMMUNITY!


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