Need car audio help! Did I fry my car amp or sub? (detailed) UPDATE: PROBLEM SOLVED!!! =)

psteng19

Diamond Member
Dec 9, 2000
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My old setup wasn't cutting it, and it was overheating

Old setup:
**
Sub was Kenwood (forgot model #, but ~150 watts RMS), powered by US Acoustics USA2050 (bridged 160 watts mono)
A very cheap begginers setup.

I used an amp kit as suggested by many, some lesser known brand (forgot which), 8 gauge, 30 amp fuse.

The problem was that the amp overheated within 45 mins or so, and some told me that the amp was not enough to power a sub, and perhaps I needed thicker gauge wire.
**

So I decided to replace that setup with an MTX setup:
**
MTX Blue Thunder Pro 752 and a "matching" MTX Blue sub.
I don't have the specs as they are discontinued and I can't find it online (something like 250 watts RMS).
(I bought it at the sound domain forums from someone locally).
**

I unplug the old setup (USA/Kenwood), replace with new (MTX). So far so good.
I set the gain to a little over halfway, and head unit (Pioneer DEH-P7300) to 3/4.

It's working fine, pumping deep rumbling bass.
A couple of minutes, the bass would cut off for a second, on for 30-45 seconds, cut off again, on, off, etc.

I turn off the system, check the wiring (thinking it was loose) but all is fine. Turn it back on, it does the same thing.
5 minutes later, all bass is lost, and the power LED on the amp goes out.

I check both fuses, they are fine.
I check for power with voltmeter and I'm getting readings for power/gound, and remote/ground.

I'm stumped, so I hook up the old amp, and it's not working as well.
Again, getting power on the leads, but no bass and no LED.

Is it the amp(s)? sub? head unit? wiring?

Help is greatly appreciated.
Thanks in advance.
 

Mrburns2007

Platinum Member
Jun 14, 2001
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The cycling on and off is most likely the amp overheating or speaker impedance is to low or maybe a short or maybe a problem with the head unit not be able to supply enough to keep the remote turned on. The fact that you can't get it to power up isn't a good sign. You need to remove the amp and try it on a test bench to see if it is faulty or if it's just not functioning right in your car (bad wiring maybe).

 

Spoooon

Lifer
Mar 3, 2000
11,565
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Double check that your sub is hooked up to the amp correctly. ie, positive to positive, negative to negative. I know it sounds stupid, but you never know when you've made a simple mistake. Other than that, post the impedence of the woofer and the loads the amp can handle.
 

psteng19

Diamond Member
Dec 9, 2000
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Best specs I could find here.
Apparently, the 752 is the 152 replacement.

37.5 watts RMS into 4 ohms @ .05% THD
75 watts RMS into 2 ohms @ .1% THD
150 watts RMS bridged 4 ohms @ .1% THD
280 watts Dynamic Power (IHF202) into 4 ohms

I have no clue what specs on the sub are :(

I'm using low level RCA inputs.

All wiring is good (power, ground, remote).

What's really stumping me is that BOTH amps aren't working now.
They're getting power (tested with voltmeter at the inputs), but the power LED's are not lighting up on both, and obviously not pumping out sound at the sub.

That leaves the amps out of the equation, no?
So it's the wiring or HU that I'm suspecting to be foul.

I would test the amp out on someone else's setup to see what happens with it in their car, but I just moved, and don't know anyone locally.
 

helloedchen

Diamond Member
Jan 7, 2000
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www.gideontech.com
had the same problem with the bass coming in and out. check the wire, notice my ground cable was popping out when i hit bumps. screwed that back in tighter and haven't had an issue since
 

Colt45

Lifer
Apr 18, 2001
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well, i guess pull it out, hook up a walkman, the amp, sub, and use a car charger (perferably charger&battery together), and see how it goes.

is it turning on if you connect the remote to live? maybe something went faulty with the remote send.
 

psteng19

Diamond Member
Dec 9, 2000
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Originally posted by: GideonX
had the same problem with the bass coming in and out. check the wire, notice my ground cable was popping out when i hit bumps. screwed that back in tighter and haven't had an issue since
Hey, that's the exact thing I was thinking, because that was happening as I was rolling over bumps. I thought it'd just go away after I tightened the bolts.
But instead, the amp died :(

:Q:Q:Q:Q:Q:Q:Q:Q:Q:Q

OK, I may have stumbled upon the problem.
The battery is supposed to supply 12 volts DC right?

I pulled out the analog voltimeter and it measures 12 vdc with the ACC off.
(I was previously a ghetto meter that shows power/no-power only).

Turn the key to ACC, and I'm getting a very low reading at the amp, something like 2-3 volts, probably not enough to power the amp.

Same with the remote lead (which I connected to ACC because I had problems with the remote lead - which is no problem because I have the stereo on all the time).
Low readings there too.

Is this the cause of the problem?
If so, what's causing the low voltage, and what's the fix?

Thanks again guys.
 

Colt45

Lifer
Apr 18, 2001
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hmm.. I'm not too sure about ACC (I've never used it)

I've always put the +12 straight to the battery terminal, and connected the ground, to well.. uh.. ground :D (- on the battery would be fine too)

kind of a bitch running things through the firewall though...
 

Spendthrift

Senior member
Oct 22, 2001
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speaking from experience, all my problems have been related to poorly grounded amps.

it should work in the ACC position, i can run both my amps while in the ACC position. does the amp work if the car is running?


if neither amp is working it really sounds like a wiring problem to me. check to see if the wires are shorting out somewhere or not grounded well enough. thats about the best i can think of.
 

psteng19

Diamond Member
Dec 9, 2000
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I did some further testing with the voltimeter.
@ battery: ~12 volts car off, ~14 volts engine running
@ amp: ~12 volts car off, ~4 volts acc or engine running

I'm losing voltage (current?) somewhere.

I'll check for wiring.
 

Mrburns2007

Platinum Member
Jun 14, 2001
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Your amp should be wired directly to the battery (postive lead) use a heavy wire like 4 guage multi stranded, the amp should be grounded well near where it is.

 

d33pt

Diamond Member
Jan 12, 2001
5,654
1
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check your ground cable to the chassis and your wiring onto the battery... make sure the ground is to an unpainted surface, if it's painted, then scrape it off... make sure the positive cable going to the battery is not corroded and tight connection.. i'm almost positive that is your problem.. it gets enough of a connection for you to see 12v when everything is off, but as soon as there is current draw, there's not enough of a connection so the voltage just drops..

even if nothing seems wrong..just take off all those connections and scrub it with something abrasive like sandpaper or steel wool...
 

psteng19

Diamond Member
Dec 9, 2000
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Your amp should be wired directly to the battery (postive lead) use a heavy wire like 4 guage multi stranded, the amp should be grounded well near where it is.
Yup, directly to battery with 30 amp fuse in between, but on 8 gauge wire. Ground is to chassis in trunk - scrubbed paint off with sandpaper.

check your ground cable to the chassis and your wiring onto the battery... make sure the ground is to an unpainted surface, if it's painted, then scrape it off... make sure the positive cable going to the battery is not corroded and tight connection.. i'm almost positive that is your problem.. it gets enough of a connection for you to see 12v when everything is off, but as soon as there is current draw, there's not enough of a connection so the voltage just drops..

even if nothing seems wrong..just take off all those connections and scrub it with something abrasive like sandpaper or steel wool...
Yup, I sanded it off in my first install (kenwood/us acoustics), and it worked great.

I don't know if this is it or not, because it was working this afternoon, and it just stopped working suddenly.
That was the MTX setup. I had it going for 5 minutes, everything sounded good... it started turning off/on and then 5 mins later, it totally stopped working.
Something busted in bewteen that time.
I thought I had the gain too high on the amp, and it couldn't handle it.

I'm going to try to re-wire everything tomorrow.
 

jamautosound

Diamond Member
Oct 15, 2000
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What type of fuses - the wafer or the tube type?

I had an issue like yours on my setup, and I had two-guage wire going to a gold block 4-fuse splitter. One of the fuses (tube type) was bad. It didn't blow out, but became disconnected from within the tube itself. So when the metal within the fuse heated up it flexed enough to stop the connection.

Otherwise re: the low power thing, it sound like your acc wire is hooked up incorrectly to the amp. When you say you're 2 or 3 volts "at the amp" I assume you mean at the 12volt connection? Not at the remote turn on?

P.S. contrary to my nic, it's been quite a long time since i've fiddled with car stereo stuff.
 

psteng19

Diamond Member
Dec 9, 2000
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OMG, you guys called it!!

It was a poor ground.
I don't believe it... I feel like such an idiot...
Today, as I was twiddling with it, as I moved the wires around with the system on, the bass would come in for a split second, and then go away.
This told me that nothing was damaged, so I went through all the wiring, took it apart, re-sanded the ground surface and VOILA!!!

OMG the bass pounds like a mofo!

Truly greatly for all the help guys! Thanks!

Oh, one note, is 10 gauge wiring suffice for a relatively light setup such as this one?
150-250 watts RMS.
 

phatcow

Platinum Member
Nov 25, 2000
2,266
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ten guage? isnt that kind of small? i know people using 10 guage as speaker wire.
 

Spoooon

Lifer
Mar 3, 2000
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202
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Oh, one note, is 10 gauge wiring suffice for a relatively light setup such as this one?
If you did it yourself, I wouldn't worry about it. If you are paying a shop, just get 4 gauge installed incase you decide to upgrade your amps to something more powerful. Get a powerblock also, helps keep things tidy. ;)
 

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