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Author Topic: Measuring amplifier voltage output with a multimeter  (Read 50456 times)

jack smith

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Measuring amplifier voltage output with a multimeter
« on: September 30, 2009, 01:40:18 pm »

Hi guys, I got just a quick question. I've bought myself a multimeter so I can test the asmplifiers in ym system to see if they're getting enough voltage to give out the power they're supposed to give out, but i'm curious as to which setting on the multimeter do I need to set it to in order to do that. I just tested a 9v battery to practice and set the multimeter to 20 volts and got a reading of 7.83 volts. I live in the uk, so would I set the multimeter to 200 volts or 600 volts to check the amplifiers output at the speaker terminals?

I listened to you guys when you said that even though I set the gain structure and don't exceed 0db on the mixer, I might need to run the vu meters into the yellow lights in order to get the right voltage for the amplifer to give out the power its supposed to.
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Whit Hutchinson

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Re: Measuring amplifier voltage output with a multimeter
« Reply #1 on: September 30, 2009, 01:57:29 pm »

You will need to set your meter to the 600v setting in order to read anything over 200v.   Simply touch the leads to the mains outlet at the wall or in your rack to see what the voltage is at your amps.

If you have another outlet on the same circuit, you can insert the leads as the system is playing near full volume and see if you are having large voltage dips.  I don't think you guys suffer from that as much as we do here in the US.  

You silly UK people with your stiff voltage supplies  Rolling Eyes



Edit:

And I just realized that you are trying to check the voltage from the speaker terminals.  You will need to set it to something in the 100v to see the speaker output terminal voltage.  Be sure to select the AC voltage selection as well when testing speaker output.
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Mike Christy

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Re: Measuring amplifier voltage output with a multimeter
« Reply #2 on: September 30, 2009, 02:42:33 pm »

Jack,

If your measuring the output of the amplifier and not the AC wall socket the 200V AC setting will be fine. Use the AC setting, not DC as when you measured the battery.

To get an accurate reading it is best to test with a steady state test signal, such as a sine wave, not program or pink noise material. One usually does not do this with the speakers connected either - so this will cause you a problem if your trying to see if your mains are stiff enough - Im kind of confused at what your testing is to accomplish.

Your meter will measure the AC RMS value of the signal. Multiply this value by 1.414 to calculate the peak value. To see the full output voltage swing at the amp output terminals apply a test signal at the amp's sensitivity voltage as measured at the input, RMS.

edit: And if your meter only supports line frequencies, you will only be able to test at 50Hz/60Hz.

Mike



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jack smith

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Re: Measuring amplifier voltage output with a multimeter
« Reply #3 on: September 30, 2009, 07:43:30 pm »

Whit Hutchinson wrote on Wed, 30 September 2009 12:57


And I just realized that you are trying to check the voltage from the speaker terminals.  You will need to set it to something in the 100v to see the speaker output terminal voltage.  Be sure to select the AC voltage selection as well when testing speaker output.


My multimeter doesn't have a 100v setting. Here's a picture of it :
http://www.diy.com/diy/jsp/bq/nav.jsp?action=detail&fh_s econdid=9288723&fh_view_size=10&fh_location=%2f%2fca talog01%2fen_GB&fh_search=multimeter&fh_eds=%C3%9F&a mp;fh_refview=search&ts=1254353708844&isSearch=true

As you can see, on the AC side, its only got 200v and 600v, while on the DC side its got 2v, 20, 200v and 600v.

I want to find out the voltage going to my speakers because I want to make sure that the correct line voltage is going to the amplifier to produce the output its rated as giving out. I've seen on the Crown K2 data sheet that it says it has a voltage gain of 23.88db at 1.4 volts sensitivity and 25db gain at 3.0 volts sensitivity. I'm not sure what that means, but I know if I dont put enough line voltage into the amplifier, I wont get as much volume as I could safely get without clipping the amplifier.
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Art Welter

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Re: Measuring amplifier voltage output with a multimeter
« Reply #4 on: September 30, 2009, 08:25:04 pm »

jack smith wrote on Wed, 30 September 2009 17:43

Whit Hutchinson wrote on Wed, 30 September 2009 12:57


And I just realized that you are trying to check the voltage from the speaker terminals.  You will need to set it to something in the 100v to see the speaker output terminal voltage.  Be sure to select the AC voltage selection as well when testing speaker output.


My multimeter doesn't have a 100v setting. Here's a picture of it :
  http://www.diy.com/diy/jsp/bq/nav.jsp?action=detail&fh_s   econdid=9288723&fh_view_size=10&fh_location=%2f%2fca   talog01%2fen_GB&fh_search=multimeter&fh_eds=%C3%9F&a mp;a mp;a mp;fh_refview=search&ts=1254353708844&isSearch=true

As you can see, on the AC side, its only got 200v and 600v, while on the DC side its got 2v, 20, 200v and 600v.

I want to find out the voltage going to my speakers because I want to make sure that the correct line voltage is going to the amplifier to produce the output its rated as giving out. I've seen on the Crown K2 data sheet that it says it has a voltage gain of 23.88db at 1.4 volts sensitivity and 25db gain at 3.0 volts sensitivity. I'm not sure what that means, but I know if I dont put enough line voltage into the amplifier, I wont get as much volume as I could safely get without clipping the amplifier.


Jack,

As has been pointed out, voltage readings on music will not tell you much, you need to use sine wave tones, which can burn speakers up rather quickly.

Running the amp without a load won't load the mains down.

As well as checking the mains voltage with the meter to check for voltage drop, a regular house lamp plugged in on the same circuit with the amp will dim if there is instantaneous voltage drop.  
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Don Ernst

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Re: Measuring amplifier voltage output with a multimeter
« Reply #5 on: September 30, 2009, 08:35:33 pm »

The correct way to use a meter, if you do not know which range to use, is to start at the highest range and work your way down the ranges until you get a reading you can use.  That way you won't damage the meter.
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Don Ernst
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Ivan Beaver

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #6 on: September 30, 2009, 10:35:20 pm »

jack smith wrote on Wed, 30 September 2009 19:43

[I want to find out the voltage going to my speakers because I want to make sure that the correct line voltage is going to the amplifier to produce the output its rated as giving out. .


First of all you are talking about two different (or more) things.

The gain of the amp is fixed in the the two positions-the AC voltage does not change that.

If you find that your AC mains are not high enough-what do you plan on doing about it?  There is nothing you can do-except use larger AC cables and possibly tie in power (not recommended for you).

And if the voltage is low coming to the building-well then that is the way  it is-deal with it. Rolling Eyes

There is no way you will be able to measure any type of output voltage with that meter (it is not fast enough)-unless it is sine waves and right around 60Hz.  And if you try to put sine wave to your loudspeakers at full power-you can kiss them goodbye.
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Whit Hutchinson

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #7 on: September 30, 2009, 11:23:54 pm »

Maybe I will deal with it IVAN!

http://www.matts-place.com/intermodal/part1/images/jrl/cat40_jrl.jpg


Completely overkill and at the venue's expense of course.   Very Happy
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I have learned in my life:

-Pretty girls don't stay single long
- KF 850s  over SB 1000s per side was designed to be a percussion instrument rather than a "soundpretty thing".

jack smith

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #8 on: October 01, 2009, 03:53:10 am »

Thanks guys. I was under the understanding that I could measure the output voltage going to the speakers and be able to tell if there's enough voltage to give out the full power of the amplifier.I'm trying to learn more about the technical side of this so I can get the best out of my system, but its not easy. Was I right about how to set gain structure? I mean, many sound engineers who work for big hire companies have told me thats the way they do it, and that way is kind of standard practice here in the uk. How do you guys set system gain structure? I use a pink noise test tone like I said, then turn up any level controls so every piece of equipment is only just hitting the red lights, then, turn the front wource down and then I know the whole system clips at the same level.
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Ivan Beaver

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Re: Measuring amplifier voltage output with a multimeter-What ya gonna do
« Reply #9 on: October 01, 2009, 07:41:03 am »

The biggest advantage of proper gain structure is dynamic range.  I really doubt you are concerned with that.

There is nothing you can do-or nay setting you can make that will allow you to get more level out of your system-that is determined purely by the cabinets used and the amplifier power.

But you can make the quiet moment quieter-by lowering the noise floor.  I get the impression there are not many quiet moments during your events.

Why bother measuing the input voltage-it is what it is and you can't do anything about it.

And if it is a little bit low-I really doubt you will be able to tell if you are not getting full power to the loudspeakers.  It would only be a couple of dB at most.

Don't waste your time on things you cannot do anything about.

You can't "make sure" you are getting the proper voltage.

What are you going to do-call up the power company and say "Hey I'm Jack and I am at so and so address and the voltage is a tad low-can you crank up the voltage at the plant so I can make my sound system as loud as it can possibly go" Laughing

What you need to do is to bring more rig than you need.  That way you don't have to woory about the voltage so much (It sounds like you are going to use it as an excuse "well it wouldn't get as loud as I want because the voltage is low" Rolling Eyes NOT!, AND you don't have to worry so much about tearing up your gear-whcih I get the feeling is going to be a common occurance.  It will be if you always run your rig at full potential.
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For every complicated question-there is a simple- easy to understand WRONG answer.

Can I have some more talent in the monitors--PLEASE?

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