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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Audio Measurement and Testing => Topic started by: Greg g. Pierce on January 29, 2012, 08:28:22 AM

Title: How to measure output of power amp
Post by: Greg g. Pierce on January 29, 2012, 08:28:22 AM

I have two crown xls802 amps, one is noticeably louder that the other. My only means of testing so far has been to check all inputs/outputs, etc, then switched the speaker cables on the two amps, and one amp is apparently putting out less than the other. This amp was recently worked on, still under warranty, I never noticed until now that it's this way. Is there a way of measuring the out put. I probably don't have the required meter unless an ohm meter will work somehow. Just wanted a concrete answer for myself and the repair shop before I call them back. I was told the output (something) cant remember now, was blown and replaced.

Thanks

Title: Re: How to measure output of power amp
Post by: Ivan Beaver on January 29, 2012, 09:18:35 AM

Quote from: Greg g. Pierce on January 29, 2012, 08:28:22 AM

I have two crown xls802 amps, one is noticeably louder that the other. My only means of testing so far has been to check all inputs/outputs, etc, then switched the speaker cables on the two amps, and one amp is apparently putting out less than the other. This amp was recently worked on, still under warranty, I never noticed until now that it's this way. Is there a way of measuring the out put. I probably don't have the required meter unless an ohm meter will work somehow. Just wanted a concrete answer for myself and the repair shop before I call them back. I was told the output (something) cant remember now, was blown and replaced.

Thanks

There is "proper measuring" and then there is comparitive measuring.

You can do a comparitive measurement by simply using a sine wave as an input. Turn the amp levels all the way up.

Use you VOM on the AC scale and turn up the signal (not using the amps controls-but on a mixer/preamp etc) untill you get say 20V on the output.

Now move everything (without touching any gain controls) and measure the other amp output.  It should read the same.

I don't know about that model of Crown, but many Crowns have a selectable gain switch on the back-or under a cover or inside etc.  Make sure these are both the same.  that would be my first suspicion of the difference in output.

Title: Re: How to measure output of power amp
Post by: Stu McDoniel on February 16, 2012, 11:07:53 PM

Quote from: Greg g. Pierce on January 29, 2012, 08:28:22 AM

I have two crown xls802 amps, one is noticeably louder that the other. My only means of testing so far has been to check all inputs/outputs, etc, then switched the speaker cables on the two amps, and one amp is apparently putting out less than the other. This amp was recently worked on, still under warranty, I never noticed until now that it's this way. Is there a way of measuring the out put. I probably don't have the required meter unless an ohm meter will work somehow. Just wanted a concrete answer for myself and the repair shop before I call them back. I was told the output (something) cant remember now, was blown and replaced.

Thanks

Output Transistor/s?  Recently having it worked on is your first clue.  Take the measurements as suggested by Ivan
and then send it back for ajustment/repair.    Did crown do the waranty work or a third party?   They might have replaced
the blown output transistor/s and did not address the other components that are out of tolerence and causing a bias issue.

Title: Re: How to measure output of power amp
Post by: John Roberts {JR} on February 17, 2012, 08:12:30 AM

Quote from: Greg g. Pierce on January 29, 2012, 08:28:22 AM

I have two crown xls802 amps, one is noticeably louder that the other. My only means of testing so far has been to check all inputs/outputs, etc, then switched the speaker cables on the two amps, and one amp is apparently putting out less than the other. This amp was recently worked on, still under warranty, I never noticed until now that it's this way. Is there a way of measuring the out put. I probably don't have the required meter unless an ohm meter will work somehow. Just wanted a concrete answer for myself and the repair shop before I call them back. I was told the output (something) cant remember now, was blown and replaced.

Thanks

Did you try swapping the inputs too?

JR