how to verify or cross check RMS watts of audio amplifiers

Audioguru

Joined Dec 20, 2007
11,249
The video is wrong because it uses a DMM to measure the 1kHz output from the amplifier.
Most DMMs are designed to accurately measure 50Hz or 60Hz from the mains but give a reading that is too low at higher frequencies.
 

R!f@@

Joined Apr 2, 2009
9,747
You guys are too much for me.

OP is designing or rather manufacturing.

So any one with the right mind would know IF he is manufacturing he or she should know everything about Audio or PA or whatever amps he is going to make & sell.
Let that may be ...RMS output Voltage or Watts or THD.

I do not think any one manufacturing equipments have anything to ask from any one.
 
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The video is wrong because it uses a DMM to measure the 1kHz output from the amplifier.
Most DMMs are designed to accurately measure 50Hz or 60Hz from the mains but give a reading that is too low at higher frequencies.
It may be wrong, but for me the DMM shows the same voltage all the way from 20Hz to 20kHz with minimum rolloff at higher frequencies.
 

R!f@@

Joined Apr 2, 2009
9,747
U cannot measure RMS Voltage from a DMM above 100 Hz or so.

At higher frequencies, a scope is the choice.

Even I don't trust my fluke over 400Hz.

It may be wrong, but for me the DMM shows the same voltage all the way from 20Hz to 20kHz with minimum rolloff at higher frequencies.
Wake up Mate.
 

thatoneguy

Joined Feb 19, 2009
6,359
U cannot measure RMS Voltage from a DMM above 100 Hz or so.

At higher frequencies, a scope is the choice.

Even I don't trust my fluke over 400Hz.



Wake up Mate.
Fluke 87-V drops to ±2% accuracy at 20kHz (arbitrary wave), and ±5% at 200kHz (sinewave only), which is the maximum bandwidth.

They even have a Low-Pass switch for measuring the fundamental of PWM signals, so I think it's capable.
 
You don't believe me, fine. I take back everything i said about my method.

I suppose you could also just use a FW bridge made up with 1N4148's and a capacitor to measure the peak voltage and divide that with 1.414 to get the RMS, though there you get a 0.7V loss due to the forward voltage drop of the diodes, unless u go opamp and build a precision fullwave rectifier.
 

thatoneguy

Joined Feb 19, 2009
6,359
You don't believe me, fine. I take back everything i said about my method.

I suppose you could also just use a FW bridge made up with 1N4148's and a capacitor to measure the peak voltage and divide that with 1.414 to get the RMS, though there you get a 0.7V loss due to the forward voltage drop of the diodes, unless u go opamp and build a precision fullwave rectifier.
Depends on the brand of meter, basically. Some of the new ones have some pretty advanced features, but calibration is an issue (I guess lack of ability to calibrate is the issue).

What is the make/model of your DMM?
 

R!f@@

Joined Apr 2, 2009
9,747
Expensive fluke meters can measure. I don't think what I have can.

You don't believe me, fine. I take back everything i said about my method..
U don't have to take everything back. you lack experience me thinks :p

I suppose you could also just use a FW bridge made up with 1N4148's and a capacitor to measure the peak voltage and divide that with 1.414 to get the RMS, though there you get a 0.7V loss due to the forward voltage drop of the diodes, unless u go opamp and build a precision fullwave rectifier.
That will work for 30 to 100 Hz. Mostly with El-cheapo's
 

studiot

Joined Nov 9, 2007
4,998
Instrument suppliers offer comapct audio test sets where important features such as a calibrated low distortion oscillator, a calibrated audio voltmeter and sometimes non inductive loads are combined into one instrument.
This allows manufacturers and laboratories to perform a wide variety of tests including power on audio amplifiers.

The photographs show a couple of such instruments. One is a bench instrument the other a neat portable battery operated instrument. Sorry but I do not have anything more modern - these still work well.
 

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thatoneguy

Joined Feb 19, 2009
6,359
Ha !! u did not know my KW amp is an over unity device....:D

Can you beat that ? :cool:
I have 2.5kW on three circuits, but I cannot claim any overunity.

I did have the police show up to a report of "shots fired" when I was watching the beach scene in Saving Private Ryan. :eek:
 
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