How to function test an amp w/o speakers.

[Shelbysguns]

I found a local guy selling a rockford 325w amp for $45. The amp is supposed to be working, but the guy has already sold his subs, so how do I test the amp? I think it is still hooked up in his car. Could I use a voltmeter? How would I do so? Thank you for helping a noob.

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[ecko_0113 10+ year member]

Get a mutimeter set it to ac and put the leads on the speaker out puts the voltage should fluctaute as you change the volume

 

[Pataforce8 10+ year member]

^ This. I would also burn some test tones to a CD so that the voltage will be constant for a given volume level.

 

[Bassin Buick]

also play tones with the amp on dc. if you see significant DC voltage on the terminals do not buy it.

 

[dragonrage 10+ year member]

also play tones with the amp on dc. if you see significant DC voltage on the terminals do not buy it.

If you measure an AC signal with your DMM set to DC, it WILL register a voltage, and that does NOT mean that the amp is outputting DC. This is not good advice.

It would read the average voltage, which is 0.637 times the peak voltage for a steady waveform. AC mode will read the RMS voltage, which is 0.707 times the peak voltage.

However, measuring a DC signal with the DMM on AC mode will register 0 volts if either the output or the DMM itself is capacitively coupled. That doesn't matter for this case, though.

By the way, some amps don't like being run without a load. I wouldn't recommend this test. I'd recommend bringing some sort of sub/speaker with you to test it on, even if low volume.

 

[thevic24 5,000+ posts]

If you have a speaker laying around(even a small home speaker) take that and use it to test with.