Question about US Acoustics USX-4065 Car Audio Amplifier

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US Acoustics USX-4065

My amp seems to cycle on and off when cold. It works great all summer long, but as soon as winter rolls in it is useless. It has done this since new. Just after I bought it I read that this amp had this problem, but now I can't seem to find anyone else with the same problem. I run the bass tube on channels 3 and 4 bridged and a pair of Jensen 6x9's on 1 and 2. It is beyond warranty now and US Acoustics would not admit to any design problems and said I could return it for repair. Any suggestions?

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  • Anonymous Feb 20, 2008

    same happens to me, I think its broken from Nov-April, then it magically fires back up



2 Answers

Yeah, mine does the same. i think its shot from nov-april, then it magically fires back up

Posted on Feb 20, 2008

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  • 133 Answers

My suggestion is to take it to a local repair shop and have them look at it

Posted on Dec 06, 2007


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Red light is on amp wont work worked before then all of a sudden the light came on?

There is a possibility that there is a cable which was coming in contact with metal wearing it out eventually and causing a short making the amplifier go into protect or you have a shorted/damaged speaker. Check your cables. With the info you provide, thats the best i can do hope this helps dreamsystems

Feb 08, 2011 | US Acoustics USX-4065 Car Audio Amplifier

3 Answers

What motor oil weight should I be using on my 96 olds 88....we live where the winter temps can go as low as -10 F and as hot as 95F in the summer

5w 30 or 10w 30 during the winter. After an oil change... check your oil after 200-300 miles of use. Is the level the same? If so your weight is fine. If it drops, it's to light of an oil and your engine is now "drinking it" like fuel, move to a heavier weight. As far as Changing between winter and summer. Changing Oil weights is not bad for your motor so if the winter you go with 5w 30 and it works, great, shoot for the same during the summer. If it seems to "drink it" during the summer using this weight, go up to the next (10w 30)

That being said. Changing from natural oil, to synthetic, back to naturual , or vice versa... swapping back and forth between these KINDS of oil has been known to cause damage. so whatever weight you decide on, stick with one "type", natural or synthetic.

Feb 27, 2010 | 1998 Oldsmobile 88

1 Answer

So i have this usx 4085 that someone threw in with some twelves on a deal, now is it even worth it to hook them up together or just buy another amp?

It depends on the quality of the 12s and voicecoil configuration.
Do you know the lowest impedence the amplifier will operate? is it bridgeable?
Howabout any low pass crossovers built in?
I would wait for a better amplifier than risk damaging the 12s if they are worth anything.

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Nov 25, 2009 | US Acoustics USX-4085 Car Audio Amplifier

1 Answer

My amp plays but it smokes

Please, Please, stop using it, the fact it plays is a malfunction in itself, so get it fixed or get a new one b4 you light your car on fire...

Oct 07, 2009 | US Acoustics USX-2100 Car Audio Amplifier

1 Answer

No sound out of it, took it apart and found one of the Irfz44n mosfets burned up and the resistor right beside it burned too, What would cause this?Thanks

Hello rjhunting,

Most often the output MOSFET's and associated circuitry will burn out when the amp draws excessive current. And excessive current draw is most often caused by operating the amp into an impedance that is too low. Of course, depending on the age and actual use, the amp could have failed from normal use. The US Acoustics USX-4085 is a relatively good quality low-end amp that was manufactured with excellent components.

All of their amps manufactured after 2001 carried a 3-year warranty. But when operated in "tri-mode", with normal speakers and a subwoofer, the subwoofer minimum impedance rating was 8 ohms. And the normal speakers should be operated through a high pass capacitor while the sub needed a 15.9 mH low pass filter inductor.

The MOSFET's and resistors can probably be replaced at a qualified electronics shop. If you are somewhat handy with a soldering iron and have a controlled temperature soldering station, you can do it yourself. Parts are available from: and

Hope this helps.

Sep 27, 2009 | US Acoustics USX-4085 Car Audio Amplifier

1 Answer

Amp blows the fuse every time.

it aint the wire, the bigger the better.
try checking your ground, if there any rust clean with sandpaper. if your gain and freq is cranked it will blow fuses and cut out, cuz the protect mode kicks in

May 04, 2009 | US Acoustics USX-2100 Car Audio Amplifier

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