calculating output power

[dwhutchens]

I am trying to calculate the output power of a Sunn bass amp. I've got two 6550s into an 8 ohm dummy load. I can get just about 30v peak at 1khz before the signal clips. With the formula I found I came up with about 56 watts rms. Does that sound right?
David

[Enzo]

Sounds about right.

[dwhutchens]

Thanks Enzo,

looks like I might have got at least one thing right this weekend, now if I can just catch this stupid mouse in my basement that apparently doesn't like peanut butter.
David

[Bruce / Mission Amps]

looks like I might have got at least one thing right this weekend, now if I can just catch this stupid mouse in my basement that apparently doesn't like peanut butter.
David

Was that 30v as measured in your O'scope or with a "rms" reading AC voltmeter?

[dwhutchens]

That was 30v peak or 60v p-p measured on my oscope.
David

[Enzo]

Then your reading is as accurate as the scope display plus your ability to interpret it. As a ball park estimate, it should be close.

[dwhutchens]

So should I be using the scope to determine when clipping starts and an rms meter to measure the voltage drop on the dummy load to get the most accurate reading? I have an old fluke bench meter, I'm not sure if its rms or not. I'm not in front of it right now and I don't remember the model number.
Thanks,
David

[oc disorder]

I find reading it from the scope is close enough for R'nR.

P (watts rms) = V p to p divided by 2 multiplied by
.707 (to convert to R.M.S.)
square it then divide by the load in ohms
so 50volts p to p becomes 25 x.707 = 17.675
17.675 squared = 312.40562525
divided by 8 (ohms) =39.050703125 watts rms

so 30 volts peak x .707 = 21.21 volts rms
21.21 squared = 449.8641
449.8641 divided by 8 (0hms) =56.2330125

'cuse the scrawl

mind you those 200watt 20 buck plastic computer speakers look good value..!

[Enzo]

Even if your meter is not "RMS" it will still be close. Use a sine wave test signal.

[dwhutchens]

Yea, I was using a function generator set for a 1khz 100mv sine wave.
David