"Trevor Wilson" wrote in message
...

"tony sayer" wrote in message
...
In article , Arfa Daily
writes
Ok, so who knows a bit about measuring audio power ? Setting aside any
furious arguments about peak power, rms power, average power,
backpeddling
average peak music power on any given friday in March etc, does an audio
power meter sum the power in both half cycles to arrive at a reading, or
just one.

I guess what I'm asking is half wave reccy ahead of the meter, or full
wave
bridge ?

Arfa



Is this the arfa daily who's a service tech?..


FWIW if its just the output of an audio amp I just use two bloody great
8 ohm resistors on a large heatsink with stout cables to reduce ohmic
losses, and connect that to the amp and use me trusty Fluke bench DMM to
measure the AC power developed when running a sine wave with the Hewlett
Packard distortion analyser keeping note of the distortion level to see
when its going into clip.

Measure that at a few different frequencies and square the AC measured
volts and divide by the 8 'ommes and thats the RMS power.

Sufficient and accurate and IMHO a good indication of what the amp will
develop.....

**Yep. Good enough for day-to-day stuff. I use the following:

http://uk.farnell.com/jsp/endecaSear...=9508180&N=401

A bunch of those nice, aluminium clad, 50 Watt resistors from Farnell.
They're bolted to a chunk of extruded aluminium rectangular tube. There's
a fan on one end and a thermal switch on the other. When it gets hot, the
fan switches on and cools the assembly (and warms the workshop, on these
cold Winter mornings). I have a bloody big old switch, so I can choose 8
Ohms, 4 Ohms or 2 Ohms for testing. Additional to that, but less often
used, I have a 0.1uF and a 2uF cap to switch across the load to test for
stability. I also use, less frequently, a dummy load, like this one:

http://stereophile.com/reference/60/

Mine has impedance minima to around 3 Ohms and there are other
differences, but this one is pretty good. As PA has indicated, such a test
shows up many, otherwise exemplary, amplifiers as being rather bad at
operating into real loudspeakers. All monitored by a 'scope and a wideband
millivoltmeter. For a long time I used a real power meter, using an
analogue multiplier IC. It was nice and convenient.


--
Trevor Wilson
www.rageaudio.com.au


Hi Trevor

Yep, those are the exact same resistors as I am using, but in the 100 watt
flavour. Heatsink the size of the Titanic with a matching fan bolted to the
end, but mine runs all the time. Has proved very useful for repair of high
power PA amps, where the owner complains of things like " cuts out half way
through the second set ". I can now leave the amp thrashing away into this
load, with the scope hung on the socket I've provided.

Arfa