# Internal voltage drop?



## Ifixtheinternet (Jan 29, 2016)

I have an alpine Mrd-M500 mono block that's been giving me issues for quite some time.

I use it to power 2 JL 12W3V3 subwoofers @ 2ohm load.

Sometimes the subwoofers will completely cut out, sometimes go to half volume and then it is fine, sometimes for weeks. 

Today it started dropping out completely and I saw on the display it was reading 10.5 volts.
I put my multimeter on the power/ground cables while it was connected and got about the same, 10.6 volts.

Disconnected the ground from the amp and measured between the cables again, and now seeing 14.4 volts. The speaker amp also shows 14.4 volts.

The Alpine seems to fluctuate between 10.5-12.5 volts, but never shows close to 14.5.

My conclusion is the Alpine amp has some internal fault.

Does this sound like something I can replace, or is she dead Jim?

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## dumdum (Feb 27, 2007)

If your multimeter agrees with the amplifier I’d say you 100% have a power feed or ground fault, why would there be something wrong with the amp?

You need to find out which side is low by checking from other amp with good voltage’s earth to the live on the dubious supply while connected and low, if it shows 14.x test from the good voltages live to the bad supply’s ground (one or the other will reveal low voltage) then you know which side is at fault and where to remedy it 

Just work your way back down the path of conductivity until you find where the 3-4v is going... use a multimeter from the live/earth that you’ve decided is low with previous tests above and you can then sort it ??


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## Sine Swept (Sep 3, 2010)

Check that connections are tight at under hood fuse / holder as there are quite a few connections that over time can become loose. Check for any connection that is hot or appears melted.


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## Ifixtheinternet (Jan 29, 2016)

I thought getting 14.4 volts at the cables feeding the troubled amp while its unplugged proves it isn't the cabling. 

The main power cable runs to a fuse block sitting right next to the Alpine amp under the driver seat, with a 2 foot run of power wire to the Alpine, and a 4 foot run to the speaker amp under the passenger seat. 

Since the speaker amp has no issues and reads 14.4 volts while playing, I can assume the cabling is good at least up to the fuse block, which leaves only the 2 foot power run and 2 foot ground cable on the Alpine.
It is grounded to a factory mounting bolt attached to the floor pan, same as the speaker amp.

How can I figure out where the fault is if the cable tests fine as soon as I unplug it from the amp?

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## Ifixtheinternet (Jan 29, 2016)

Ok thanks! Apparently I have no idea what I'm talking about and I have more testing to do.

I'm hoping at least my 2ND assumption is correct, that since the other amp reads perfect, at the least the power run they share is good.

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## dumdum (Feb 27, 2007)

Ifixtheinternet said:


> I thought getting 14.4 volts at the cables feeding the troubled amp while its unplugged proves it isn't the cabling.
> 
> The main power cable runs to a fuse block sitting right next to the Alpine amp under the driver seat, with a 2 foot run of power wire to the Alpine, and a 4 foot run to the speaker amp under the passenger seat.
> 
> ...


You test with the amp connected so the fault is there ??

And yes I put that in a post above, your power front to distribution block is solid if the other amp is good

If it pops up to 14v when you disconnect the amp the issue is a bad connection somewhere causing voltage drop under load... one strand of cable will conduct enough current to make 14.5v with no load, but add load and it will fall through the floor due to resistance at a bad connection ??

Put the multi meter on a good known ground (use the other amps terminal if that reads correctly) then see what the voltage reads with the amp connected... work your way back to the distribution block and check there, if it’s 14.5 there which it should be I’d remake the connections at either end, the connection can only be at either end of the cable (remove it completely, strip new cable and remake both ends, don’t assume the cable is ok and just nip it up ?? If it reads 10.5 at the output of the distro, check at the other end of the fuse, wouldn’t be the first time I’ve seen a fuse go sideways and cause this exact issue

If however both ends of the cable read 14.5 using an independent good known earth then put the meter to +12v on the good voltage amp and check at the earth terminal on the amp, if it reads 10.5v there go back to its origin and check there, if you then get 14.5v at that point it’s either your earth lug connection/crimp, or the connection at the amp, it really is that simple to sort this


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## Hillbilly SQ (Jan 26, 2007)

dumdum said:


> You test with the amp connected so the fault is there ??
> 
> And yes I put that in a post above, your power front to distribution block is solid if the other amp is good
> 
> ...


This time a million!


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## Ifixtheinternet (Jan 29, 2016)

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## Hillbilly SQ (Jan 26, 2007)

Me thinks a loose connection caused that.


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## Ifixtheinternet (Jan 29, 2016)

Hillbilly SQ said:


> Me thinks a loose connection caused that.


When I installed the fuse block, I accidentally put one of the washers under the fuse, between the fuse and block.

To my dismay, I actually made this error twice, one for each fuse. I have no idea why I would have done that. 

It seems the speaker amp never drew enough amperage to be an issue, but I corrected that side.

The left screw is now fused to the block.
Time for a new block, some cable and extra fuses. 

I now retreat in shame. 

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## Hillbilly SQ (Jan 26, 2007)

Well at least you found the issue and nothing caught fire. Hopefully your amps survived without damage.


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## Ifixtheinternet (Jan 29, 2016)

Hillbilly SQ said:


> Well at least you found the issue and nothing caught fire. Hopefully your amps survived without damage.


I got the green light to purchase a new amp, when I thought it was the amp.

First I'll have to see if it's OK.
Then I'll have to decide if it's OK.



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## quickaudi07 (May 19, 2010)

Ifixtheinternet said:


> Sent from my Pixel XL using Tapatalk


I hate these connectors for fusing... Get rid of it please ! 

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## Ifixtheinternet (Jan 29, 2016)

quickaudi07 said:


> I hate these connectors for fusing... Get rid of it please !
> 
> Sent from my Pixel 2 XL using Tapatalk


Really?

I thought they were actually pretty good connectors.

They sandwich the wire between the Internal lug and socket, seemed very secure and good contact.

Edit: Looks like they don't sell this one anymore, so your wish is granted!

What would be a better style?


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## Sine Swept (Sep 3, 2010)

The hardware on the fusing is fine, I think he means the nuts on the side that connect your power wires to the block. I prefer when it is a set screw that holds the power wire into the fuse block.

Look into a Knukonceptz dual mini anl fuseholder (and some fresh fuses). They are small and affordable and usually come with fuses.

Loose connections can wreak havoc for sure. Probably worth going over the rest of the system for what its worth. You will find the longer you are in this, going back and seeing work that you've already done with a fresh eye (and knowledge) can often show us the errors of our ways.

Crimps on insulated terminals speak very loud at times.


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## Ifixtheinternet (Jan 29, 2016)

Sine Swept said:


> The hardware on the fusing is fine, I think he means the nuts on the side that connect your power wires to a block.
> 
> 
> 
> ...


Yeah that's what I was referring to.
The power wire pushes through a lug, then you wrap the wire backwards around the lug and it sandwiches the power wire.

I couldn't pull those apart if I tried.

The current Basik fuse holder has the standard screw terminals. I'm not a fan of bare wire shoved in and held with a screw.

I do have 4ga wire ferrules, but while putting one of those on yesterday at the amp, the wire pulled right out easily after tightening it down.

I'm sure the power wire connectors played no role in this failure.

Maybe a lug based block would be best?

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## Sine Swept (Sep 3, 2010)

Just get the appropriate fuse holder.

If you are using 4 gauge wire, get the 4 gauge input and your wire will fit properly with a set screw. I'm not going through all this effort to lead you astray!

https://www.amazon.com/KnuKonceptz-...nl+4+to+8&qid=1553617298&s=electronics&sr=1-5


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## Ifixtheinternet (Jan 29, 2016)

Sine Swept said:


> Just get the appropriate fuse holder.
> 
> 
> 
> ...


Thanks, I'll get that one.
It looks compact too which will be good.

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## quickaudi07 (May 19, 2010)

This is not bad at all..
















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## quickaudi07 (May 19, 2010)

The connectors are kinda expensive but I promise you.. they are wonderful and well money spend on a great install. Also power transfer..

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## dcfis (Sep 9, 2016)

quickaudi07 said:


> Ifixtheinternet said:
> 
> 
> > Sent from my Pixel XL using Tapatalk
> ...


Umm why? Those are the easiest and most secure way to do it


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## Ifixtheinternet (Jan 29, 2016)

dcfis said:


> Umm why? Those are the easiest and most secure way to do it


Yeah, I'm convinced those compression fittings are the ultimate termination type.

You get the most possible surface area contact between the wire and connector, and they absolutely will not come apart.

The damage here was caused by my careless install mistake, not the design of the block.

I've pulled that amp out and stressed those cables many times, and that block has never failed me.

I finally figured out the model Knuconceptz superceded that one with, here:

http://www.knukonceptz.com/mobile-a...ks/sp/konfused-2-way-fuse-6-way-ground-block/

I purchased that one, gonna keep the Basik block as an extra / backup block.

When I installed wire ferrules on my 4ga power / ground wire to my amps, one of the wires pulled straight out after really cranking down on it.

Bare wire with a set screw is more secure, but leaves bare wire exposed slightly which is a hazard.

These compression type fittings solve both problems. I wish my amps had them!

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## Jscoyne2 (Oct 29, 2014)

Those Knu fittings take getting used too without a doubt. I can say that once you figure them out. They are Never coming off without your help. 

There are some things i don't like though. Like not being able to take off the middle wire without taking off the left or right one first. And you have to be careful cranking them down. Ive snapped the block off the plastic holder. You have to hold the block down while turning a wrench. Its no fun but ultimately the safest method.

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## Sine Swept (Sep 3, 2010)

If you get the block that is appropriately sized to your wire, a set screw will hold that wire into the block. I would much rather get a small hex key than a wrench working in some confined spaces. I find the nut style terminal very clunky, whereas a set screw does not take much time to tighten down. Most hardware stores should sell set screws, should you lose one!

Also if you are having issue with stray wire, get a piece of heatshrink on the end of your power wire and put a 1/4" onto the exposed wire. Once heated this small portion of heatshrink will cover the exposed wire as well as pull it together also making it easier to put into the fuseblock. If you get red and black shrink, you can also color code your power and ground.


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## Ifixtheinternet (Jan 29, 2016)

Jscoyne2 said:


> Those Knu fittings take getting used too without a doubt. I can say that once you figure them out. They are Never coming off without your help.
> 
> There are some things i don't like though. Like not being able to take off the middle wire without taking off the left or right one first. And you have to be careful cranking them down. Ive snapped the block off the plastic holder. You have to hold the block down while turning a wrench. Its no fun but ultimately the safest method.
> 
> Sent from my XT1710-02 using Tapatalk


Thanks for the warning, maybe I'll clamp the blick to something when I tighten it.

Can you not take off the center one first due to danger of shorting, or is there not enough room for a wrench?

I need 3 4ga connections, maybe I can install the main power wire on one side and the amp cables on the other to get around that?

This comes with 4 4ga lugs, hopefully they can be relocated.

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## Ifixtheinternet (Jan 29, 2016)

Sine Swept said:


> If you get the block that is appropriately sized to your wire, a set screw will hold that wire into the block. I would much rather get a small hex key than a wrench working in some confined spaces. I find the nut style terminal very clunky, whereas a set screw does not take much time to tighten down. Most hardware stores should sell set screws, should you lose one!
> 
> 
> 
> Also if you are having issue with stray wire, get a piece of heatshrink on the end of your power wire and put a 1/4" onto the exposed wire. Once heated this small portion of heatshrink will cover the exposed wire as well as pull it together also making it easier to put into the fuseblock. If you get red and black shrink, you can also color code your power and ground.


Thanks, I do have heat shrink, but my concern is any amount of heat shrink protruding into the hole will be covering up metal contact area the wire needs.

I may go that route at the amp terminals where I don't have a choice.

I agree these terminals are more difficult to install/ remove, but they are also much more secure, provide a better electrical connection, and have a clean look without the need for heat shrink.

To me, the difficulty is well worth the upsides.

I rarely need to disconnect / reconnect those wires. In fact, this was the first time I ever needed to since I installed the block. So for me a one time difficulty is the only downside but there are several benefits.

If you need to redo these connections often, perhaps that becomes a bigger consideration.

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## Ifixtheinternet (Jan 29, 2016)

Well, the Basik terminal arrived with a screw stripped out. 

Good thing I bought the Konfused terminal. Guess a couple more days without bass won't hurt, right? 

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## Ifixtheinternet (Jan 29, 2016)

It's so beautiful!










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## Sine Swept (Sep 3, 2010)

Back in action!


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## Ifixtheinternet (Jan 29, 2016)

Sine Swept said:


> Back in action!


Yeah, and better than ever!

I never saw more than 12.5 volts on that amp before, I thought that was just the loss through the cable run.

But since the other amp shows 14.4v clearly something else was wrong. That fuse block connection was either worse than I thought, or there was some other issue with it.

Nothing was loose on the damaged fuse block when I took it out, however the washer that was between the fuse and block on the load side had a small chunk missing and looked burnt.

So it must have just been having the washer on the wrong side of the fuse.

I definitely won't be making that mistake again.

Never heard my subs sound so good before!

Been driving with a smile on my face the last couple days!



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