How to TEST a USED amp?

Is this amp OK?
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LMANNYR
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How to TEST a USED amp?

#1 Post by LMANNYR » Mon Nov 13, 2017 6:33 pm

How can I test a used amp before buying? Seems there alot of deals out there for used amps but don't want to be taken. I'm sure I can bring a cab and hook it up but is there a more definative way of testing? How exactly? Thanks

jimbo7
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Re: How to TEST a USED amp?

#2 Post by jimbo7 » Mon Nov 13, 2017 8:56 pm

here you go

Ipod > y-cable > amp > multimeter

Play something through the amp and use the multimeter to see if it puts out voltage. Do we really have to hold your hand?
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LMANNYR
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Re: How to TEST a USED amp?

#3 Post by LMANNYR » Tue Nov 14, 2017 12:07 pm

jimbo7 wrote:here you go

Ipod > y-cable > amp > multimeter

Play something through the amp and use the multimeter to see if it puts out voltage. Do we really have to hold your hand?

The snarky response wasn't necessary. Pro Sound is NEW to me and so is the lingo that goes along with it. Sometimes when researching a new topic/hobby, SEARCHing using the correct keywords is KEY to finding the right info. I appreciate the link. I did search that exact term in google by the way and got the SAME results prior to posting this thread. There are many videos but there all over the place. Not sure if the same principles that were used on CAR AMPs are the same with 110V AMPS.

Is the test done with full gain, min gain, etc? Does a speaker need to be hooked or can I just put leads on the outputs?

David Raehn
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Re: How to TEST a USED amp?

#4 Post by David Raehn » Tue Nov 14, 2017 12:37 pm

Play a recording od a 100Hz test tone. Test at full gain without a loudspeaker connected. Meter the outputs. Voltage at the output should be close to advertised specs.

LMANNYR
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Re: How to TEST a USED amp?

#5 Post by LMANNYR » Tue Nov 14, 2017 1:00 pm

David Raehn wrote:Play a recording od a 100Hz test tone. Test at full gain without a loudspeaker connected. Meter the outputs. Voltage at the output should be close to advertised specs.
David,

THANKS.. Short and sweet. Black and white. Thanks again.

CoronaOperator
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Re: How to TEST a USED amp?

#6 Post by CoronaOperator » Tue Nov 14, 2017 9:22 pm

I'd also fiddle with the gain knobs while playing music, make sure they aren't scratchy.

Also bring along a led flashlight and look in the vent holes to see how full of dust it is and check to see if the cooling fans are working.
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dswpro
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Re: How to TEST a USED amp?

#7 Post by dswpro » Wed Nov 15, 2017 9:18 am

I usually test one channel at a time. I connect a source like a phone, but preferably a phone through a mixer, and play music into the amp. I use a multi-meter on outputs before connecting to any speaker to make sure the amp isn't spitting out any constant or harmful voltage. With no music playing and amp inputs turned all the way up you should have no measurable DC voltage and very low or immeasurable AC voltage. Play music and turn the amp up to see how high the AC voltage gets. I also work the volume controls on each channel to make sure they at least work.

After those tests and only if they pass, I hook up a speaker and play some music to make sure the amp isn't audibly distorting. Most solid state amps are pretty reliable, but there are a few things to look for. With no input running but the volume turned up check for a high frequency whine from the speaker. This is more common for class D or lightweight switching amps than old iron amps. Doesn't mean the amp is bad, but you may want to negotiate the price down before buying and if you buy, put that amp on a sub where the whine wont be heard. If the amp has fans, make sure they are spinning. I've picked up a lot of used amps and other gear at guitar center over the years. Haven't been burned yet.

LMANNYR
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Re: How to TEST a USED amp?

#8 Post by LMANNYR » Wed Nov 15, 2017 11:05 am

dswpro and CoronaOperator, thanks for the additional tips! You guys are what make this forum great! Thank you!

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