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Old 09-08-2013, 10:33 AM
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Amp getting HOT!

I helped a buddy to get his tower speakers going as they have not worked since he has owned the boat. It has an MTX marine 900watt amp. I found out that the 4 channel option was not working for some reason so I switched it to 2 channel and turned the gain up. I was able to get sound by soon that. I set the tower speakers a little louder than the speakers in the boat and they sound good. However, after being on for 45 mins or so, the amp gets hot and goes into protect mode, turning the tower speakers off. It will come back on after it cools back down but will get hot again. What is the problem? Is there an easy fix?
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Old 09-08-2013, 11:00 AM
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Sounds like a blown amp. I had an RF amp in a thunderbird back in highschool that did the same thing. Sounds to me like the amp is bad if it is not working in 4 channel and it overheats regularly.

I'm not a guru on this stuff but there isn't any setting on the amp that should hurt the amp. The amp should be able to put out what it says it can. I mean there may be a couple switches that if both are on then it could cause damages, but simply changing channels output and gain should have no affect on the amp. It would maybe blow speakers if overpowered but never the amp.

So it sounds like the amp is bad.

Maybe Earmark or Jim can chime in. They are the resident experts here.
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Old 09-08-2013, 12:40 PM
MLA MLA is offline
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Class-A/B id guess?
Is it set to full-range or Hi-Pass? If hi-pass, whats the cross-over frequency dial set at?
How many speakers per chnl?
is it bolted directly to a carpeted wall?
Gain too hi also adds to the amps work load, so setting it at optimal or below is best.
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Old 09-08-2013, 01:18 PM
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Unsure what class. Not sure what that means exactly. I think it was set on the FR setting. There are two speakers per channel, actually only two speakers total. When it first went out, it sitting on the seat, which I just thought was the reason for it getting hot. The next time, it was just sitting propped up in the storage under the seat, out of the water and on the trailer. It was previously mounted to the side of the subwoofer box and now it is unmounted. I did tell my buddy to put a spacer between the wall and the amp to let some air flow behind it. Could it help to just put one speaker on each channel and adjusting the gain?
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Old 09-08-2013, 02:25 PM
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Originally Posted by CC2MC View Post
I helped a buddy to get his tower speakers going as they have not worked since he has owned the boat. It has an MTX marine 900watt amp. I found out that the 4 channel option was not working for some reason so I switched it to 2 channel and turned the gain up. I was able to get sound by soon that. I set the tower speakers a little louder than the speakers in the boat and they sound good. However, after being on for 45 mins or so, the amp gets hot and goes into protect mode, turning the tower speakers off. It will come back on after it cools back down but will get hot again. What is the problem? Is there an easy fix?
Use a multi-meter, set to Ohms, to check the speaker wires on each speaker, then from one speaker to another (if separate wires were run to each speaker, then from the speaker wires to the tower. If you see any continuity from the speaker wires to the tower, it will cause problems, especially if you see it on both channels- you can't combine ANY connections between the channels. It is possible that the amp has a problem- what model? It could also be a problem with at least one speaker- if you can substitute other speakers, do that.

What is the gauge of the power cables, does it have distribution blocks, were the ring terminals crimped, or crimped AND soldered (the best way)?

Do a voltage drop test on the power wires and write the results on paper- set the meter to DC Volts and connect from the battery post (NOT the terminal) to the terminal, then turn the system on. If you see voltage, you have a resistive connection. If you see no voltage (set it to the lowest scale), move the probe from the terminal to the next connection down the line, whether it's at a distribution block or the amp. If you see voltage, you have a resistive connection. Once you get all the way to the amp, look at the measurements- anything more than .1VDC total is a problem, more is a bigger problem. Repeat this on the ground cable- it's very possible to have a problem on one without having a problem on the other, but the solution MUST be found because both sides affect the amp's performance, longevity, your speakers and your ears.

If you don't see a problem when the boat isn't running, run the engine and repeat the tests. Wiggle wires while you test each connection.

If the amp doesn't work in 4 channel mode, is this with two, or four speakers? If it's with two, make sure the connections are on the correct terminals- most amps use L+/R- when in bridged mode but the switch must be in the correct position.
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Old 09-08-2013, 02:54 PM
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Quote:
Originally Posted by CC2MC View Post
Unsure what class. Not sure what that means exactly. I think it was set on the FR setting. There are two speakers per channel, actually only two speakers total. When it first went out, it sitting on the seat, which I just thought was the reason for it getting hot. The next time, it was just sitting propped up in the storage under the seat, out of the water and on the trailer. It was previously mounted to the side of the subwoofer box and now it is unmounted. I did tell my buddy to put a spacer between the wall and the amp to let some air flow behind it. Could it help to just put one speaker on each channel and adjusting the gain?
Class-A/B is the least efficient. A lot of the battery power consumed is converted to heat. Having all 4 chnls driven at a 2 ohm (2 4 ohm speakers wired in parallel per chnl) is a real work out for amp. This can add to the heat. With the amp playing for awhile, shutting down, then returning to service, does sound like thermal shut down. Moving the cross-over filter to HP, will also reduce to load on the amp. Just a few simple adjustments that might help out.
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  #7  
Old 09-08-2013, 03:54 PM
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Originally Posted by MLA View Post
Class-A/B is the least efficient. A lot of the battery power consumed is converted to heat. Having all 4 chnls driven at a 2 ohm (2 4 ohm speakers wired in parallel per chnl) is a real work out for amp. This can add to the heat. With the amp playing for awhile, shutting down, then returning to service, does sound like thermal shut down. Moving the cross-over filter to HP, will also reduce to load on the amp. Just a few simple adjustments that might help out.
An amp that's Class A/B operates in Class A at low power levels, only. It's designed to operate more efficiently at higher power levels. A Class A amp is the least efficient because it operates at about 70% bias level at all times.
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Old 09-08-2013, 04:58 PM
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Great info Jim, thanks for sharing. So who in the mobile 12v amp world is currently producing Class-A only amps? This way, others would know what to steer clear of.
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Old 09-08-2013, 05:04 PM
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Originally Posted by MLA View Post
Great info Jim, thanks for sharing. So who in the mobile 12v amp world is currently producing Class-A only amps? This way, others would know what to steer clear of.
I can't think of any because it's such an inefficient design and with 12VDC systems, efficiency is (theoretically) king. I took your comment as more of an absolute.
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Old 09-08-2013, 05:21 PM
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Originally Posted by JimN View Post
I can't think of any because it's such an inefficient design and with 12VDC systems, efficiency is (theoretically) king. I took your comment as more of an absolute.
I thought so..........no worries. It was more of whats currently available in the retail market.
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