Anyone know how to test the output of a car stereo amp?

[Spoooon]

Anyone? I had to send an amp in to get fixed and they sent it back with bigger fuses installed. I'm wondering if this is translating to increased power output.

 

[DAM]

got a volt meter?



dam()

 

[snakesnfrogs]

<< I'm wondering if this is translating to increased power output. >>




if it's got a regulated power supply, it won't affect it---what amp is it?

edit: and even if it's not a regulated power supply, it's very unlikely that you would be able to hear a difference in volume

 

[Spoooon]

I've got a multimeter and an o-scope. The power going in is around 12.5 volts. The amp is rated for 500 watts and 12.5 volts. It has 2 20 amp fuses. They replaced them with 30 amp fuses.

edit: Orion XTR 500

edit2: Even if it's not noticeable, I'd like to know what the amp is doing.

 

[perry]

They were out of 20A fuses that day so they used 30A. No big deal.

 

[tigerbait]

It could be a big deal, because I am sure there was a reason they put 20A fuses in the first place. The amp might not be rated to handle 60 amp input

 

[Spoooon]

I doubt that they were simply out of 20 amp fuses. Besides, you're not suppose to go up in rating with fuses, only down. But still, does anyone know how to measure the output of an amp?

 

[snakesnfrogs]

how to measure your own wattage

 

[Spoooon]

Cool, now I need to pick up some resistors.

 

[RossGr]

Since P=IE you can compute the current for 12.5A and 500W

I = P/E = 500W/12.5V = 40A

I am assuming that this must be 500W total -> 250 per channel so it should not need more then 20A fuses.

The size of the fuse should have no effect until it is needed. Potentialy the 30A fuses could have disastrous effects as they will not blow before the final amplifiers if a short develops in your system. Or perhaps you run to many speakers and crank the volumn.

 

[perry]

Most decent amps push out more than they are actually rated at. I have a MTX that's rated at 85W peak at 4 ohms (50x2 RMS @ 4ohms). The birth certificate that came with the amp shows it puts out 112W per channel.

I can't remember the size of the fuses on it and I'm too lazy to crawl out there and look, but they are certainly bigger than the 14A that would be required to drive the amp at it's rated power output.

My other Clarion amp is rated at 80Wx4 @ 4ohms. It has two 20amp fuses. So Clarion is putting their amp in danger by using larger fuses than necessary, huh?

60A fuse would give up to 750W. While achieving 750W is a little optimistic for an amp rated at 500W, it certainly won't pose a risk to the amp. Also keep in mind that 12.5V is almost a minimum output for car electrical systems.. Sure, they're 12V, but put a multimeter on your battery and see if you only get 12V. I've measured in the high 13.xV on my battery before, getting into the 14's is not unheard of.

 

[Viperoni]

RossGR, you're only mistake is that you're assuming that the amplifier is 100% efficient, which it isn't
Class D amps approach 95%, but class A/B are like 50% or so.....
And dont forget fuses dont blow till at least 150% of their rating.

 

[RossGr]

Efficency doesn't really matter here. The spec'ed wattage is NOT delivered to the load, but what is disapated by the amp so the straight numbers should be pretty good. All stereo amps have to be class A, that is the class which gives accurate reproduction of the input signal, class D runs at off or saturation.

Yes most electronics are designed with a safety factor, what is it? I am not sure, it's your amp you look for the limits.

The final answer is that fuses should have no effect on power, unless you are drawing enough current to be over the rated output, again it is your amp.

 

[Spoooon]

I realize that the fuses by themselves have nothing to do with power. But the fact that they used larger fuses means the amp is drawing more power than before. So, either something is wrong, or they did something that required the amp to draw more power.