Testing amplifier output

[DIGIDIGIBOMBO 10+ year member]

Hi, can i find out out how many rms an amp is outputing at his maximum?? lets say i used a 1Khz test tone and kept on turning gain up till i see a clean sine curve on the oscope, then i use a DMM lets say i got 20volts=>100rms for a 4ohms speaker. Now i i used a 40Hz test tone, again the maximum uncliped voltage must be 20volts right?(regardless of what frequency test tone i used)=>100rms for a 4ohms load right?? is it a good way to test amplifiers? And y do we use 1Khz tones for speakers and 50Hz for subs when i want to set gains using a DMM, y not different frequencies....Thx

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[KngOfThePkngLot 5,000+ posts]

**scratches head and runs away**

 

[RandyJ 10+ year member]

I'll answer this later when I have my electronics book in front of me.

 

[JimJ 5,000+ posts]

The one problem with the method you described is that a speaker is not a stable load to test into - its reactance and inductance changes depending on what frequency it's reproducing. A better way would be to run the amp into a dummy load that is a continuous 4ohm (or whatever impedance you need) regardless of what frequency is being used.

 

[Flipx99 5,000+ posts]

How does one create this dummy load?

 

[RandyJ 10+ year member]

How does one create this dummy load?

They have them for sale, try radio shcak or some other electronics store.

 

[Moe Lester 10+ year member]

buy a clamp meter and a DMM and you can figure it out

 

[Flipx99 5,000+ posts]

Is that how some stores bench test? Hook an amp to a dummy load and then measure watts with a dmm. I don't know if you can measure directly, but perhaps with a formula?

 

[RandyJ 10+ year member]

Is that how some stores bench test? Hook an amp to a dummy load and then measure watts with a dmm. I don't know if you can measure directly, but perhaps with a formula?

They measure with a clamp meter which provides a load and current I believe.

 

[Flipx99 5,000+ posts]

Are those like DMMs but intstead of the probes they have clamps? I have seen them at work (lowe's)

 

[Flipx99 5,000+ posts]

ttt

 

[bjfish11 5,000+ posts]

hey moe, how do you figure out the rms with a clamp meter and dmm? im curious, i might just have to buy a clamp meter if its not too hard to do.

 

[Raven 10+ year member]

Power = volts X amps.

1. Attach a dummy load to each channel of your amp (IE, 4ohm dummy)

2. play a sine wave with the gain set to just under clipping (you'll see it in an oscope)

3. Measure volts with the DMM, and amperes with the clamp meter. (Let's say 24 volts and 24 amps)

4. Multiply volts x amps for the wattage put into the dummy load. (24 X 24 = 576 watts at 4ohm)

EDIT:

This is to the best of my knowledge, take it with a grain of salt unless someone want's to confirm it.

Also, IIRC, the volts and amperes given out by an amp are so similar that some people just say to measure volts and square it.

 

[btnhfan 5,000+ posts]

Clamp meters cost at least 50, most of the ones I have seen are around 70.

IMO, you dont really need one unless its for competing.

 

[DBfan187 5,000+ posts]

dummy load, DMM, oscope. distortion analyzer would be nice too!