how to compute the rms output of audio amp

mozikluv · 23rd August 2003, 07:05 AM

does anyone know how to compute the rms output of an audio amplifier in the class A or AB? thanks.

Sch3mat1c · 23rd August 2003, 06:50 PM

It depends on the devices used, load resistance, supply voltage and available current. Can you be more specific?

Tim

PassFan · 28th August 2003, 01:20 PM

A rough calculation would be output voltage squared divided by speaker resistance. If your meter gives an rms measurment your done if not, multiply by .707.
Use a dummy load and an adjustable input source for more accuracy. Input to amp should be around .775v to 1v. This method does not simulate a real world load but will give you a good idea of what you have. Good Luck

jackinnj · 28th August 2003, 02:43 PM

Unless you want to buy an Agilent or Bird wattmeter, this is simple and really works -- get a decent thermometer, a thermos of at least 1 litre capacity, fill with 1 litre of distilled water, place an 8 ohm resistor (insulate the leads with heat shrink tubing) of sufficient wattage to handle the load in the thermos.

Measure the temperature temperature at rest, crank up the amplifier and measure the temperature again. 1 calorie is the amount of energy needed to raise 1 liter of water 1 degree C -- you can convert to watt-hours by just figuring in the constants.

Yes, I did the graduate labs in physical chemistry --

jan.didden · 28th August 2003, 03:04 PM

That reminds me of the student who was asked how he could compute the height of a building with the aid of a barometer. Answer: climb to the top of the building, drop the barometer, time how long it takes until impact, then using the normal formulas for accelaration under 1 gravity, calculate the height of the building....

Jan Didden

jackinnj · 28th August 2003, 03:09 PM

Quote:

Originally posted by janneman
That reminds me of the student who was asked how he could compute the height of a building with the aid of a barometer. Answer: climb to the top of the building, drop the barometer, time how long it takes until impact, then using the normal formulas for accelaration under 1 gravity, calculate the height of the building....

Jan Didden

At least you won't have to purchase a bunch of polystyrene caps to integrate the measurements with your AD536 !

btw, at one time I did ask the people in the labs at CPC (they make salad and cooking oil) for the thermal transfer constants for this application on one of my ham band transmitters -- they actually know this stuff if you are diligent enough to look.

jan.didden · 28th August 2003, 03:25 PM

Climb the stairs in the building, and put marks on the walls for every "barometer height" as you climb. At the top, go back down and count the marks. Multiply with the barometer length, gives you the building height.

Another one, anyone (yes, this is a challenge)?

jan Didden

pinkmouse · 28th August 2003, 03:34 PM

Stand far enough away so that the barometer covers the height of the building when held at arms length. Measure the actual height of the barometer, and the length or your arm, and as long as you know how far away from the building you are, simple geometry does the rest.

pinkmouse · 28th August 2003, 03:41 PM

Or...

Go to the top of the building and tie the barometer to a length of string and lower it down until it is just suspended off the ground. Start the barometer swinging, and measure it's frequency. You can then compute the height from the mass of the pendulum, and the time it takes for a full cycle.

al/should probably stop now...

James D. · 28th August 2003, 04:06 PM

How about measure the air pressure at the base of the building then measure the air pressure at the ... No don't bother it would never work...

23rd August 2003, 07:05 AM	#1
mozikluv diyAudio Member Join Date: Aug 2003 Location: Bacolod City, Neg. Occ., Philippines	how to compute the rms output of audio amp does anyone know how to compute the rms output of an audio amplifier in the class A or AB? thanks. __________________ "none but the brave deserves the fair" shakespeare

23rd August 2003, 06:50 PM	#2
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	It depends on the devices used, load resistance, supply voltage and available current. Can you be more specific? Tim __________________ Seven Transistor Labs Projects and Resources

28th August 2003, 03:25 PM	#7
jan.didden diyAudio Member Join Date: May 2002 Location: Great City of Turnhout, Belgium Blog Entries: 6	...another one: Climb the stairs in the building, and put marks on the walls for every "barometer height" as you climb. At the top, go back down and count the marks. Multiply with the barometer length, gives you the building height. Another one, anyone (yes, this is a challenge)? jan Didden

28th August 2003, 03:34 PM	#8
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Stand far enough away so that the barometer covers the height of the building when held at arms length. Measure the actual height of the barometer, and the length or your arm, and as long as you know how far away from the building you are, simple geometry does the rest. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

28th August 2003, 03:41 PM	#9
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Or... Go to the top of the building and tie the barometer to a length of string and lower it down until it is just suspended off the ground. Start the barometer swinging, and measure it's frequency. You can then compute the height from the mass of the pendulum, and the time it takes for a full cycle. al/should probably stop now... __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort


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28th August 2003, 01:20 PM	#3
PassFan diyAudio Member Join Date: Aug 2001 Location: Central FL	A rough calculation would be output voltage squared divided by speaker resistance. If your meter gives an rms measurment your done if not, multiply by .707. Use a dummy load and an adjustable input source for more accuracy. Input to amp should be around .775v to 1v. This method does not simulate a real world load but will give you a good idea of what you have. Good Luck

28th August 2003, 02:43 PM	#4
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	Unless you want to buy an Agilent or Bird wattmeter, this is simple and really works -- get a decent thermometer, a thermos of at least 1 litre capacity, fill with 1 litre of distilled water, place an 8 ohm resistor (insulate the leads with heat shrink tubing) of sufficient wattage to handle the load in the thermos. Measure the temperature temperature at rest, crank up the amplifier and measure the temperature again. 1 calorie is the amount of energy needed to raise 1 liter of water 1 degree C -- you can convert to watt-hours by just figuring in the constants. Yes, I did the graduate labs in physical chemistry --

28th August 2003, 03:04 PM	#5
jan.didden diyAudio Member Join Date: May 2002 Location: Great City of Turnhout, Belgium Blog Entries: 6	That reminds me of the student who was asked how he could compute the height of a building with the aid of a barometer. Answer: climb to the top of the building, drop the barometer, time how long it takes until impact, then using the normal formulas for accelaration under 1 gravity, calculate the height of the building.... Jan Didden

28th August 2003, 04:06 PM	#10
James D. diyAudio Member Join Date: Nov 2002 Location: North Herts, UK	How about measure the air pressure at the base of the building then measure the air pressure at the ... No don't bother it would never work...

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