Measure Output Wattage?

[The Ballzz]

Hi Folks,
I'm assuming to use an oscilloscope to measure output wattage of an amp. I've done it before, years ago on solid state amps, but can't remember the procedure. Please explain procedure, test equipment hookup and possibly the math needed to arrive at a meaningful conclusion.

Another question, is measuring the speaker leads at the speaker "AFTER" a power attenuator a semi accurate way to determine how many watts are required to achieve a certain volume/sound pressure level?

Thanks,
Gene

[xtian]

Put 1KHz sine wave at input. Hook output to dummy load. Adjust amp controls for max sine amplitude at output before clipping. That's where the scope is handy because you can see the shape of the wave. Measure output voltage as RMS, square, and divide by dummy load to get wattage. That's quick summary because typing on phone.

[The Ballzz]

xtian,
Thank you sir! I was pretty sure it was that simple, but just could not recall the details. Should I assume somewhere in the range of 1.5v to 2.3v for the input signal? Also, should I expect to see a different output at, say 400hz or 2khz?

AND

Is it just as simple to take the same sort of readings and do the same equation "POST" power attenuator? I'm not looking for gnat's ass accuracy here, but simply some ball park figures! Of course, being an oscilloscope newbie, I'll be looking for the numbers on my Fluke meter to be in agreement with graduations on my scope, just for reference! I will likely also take a look at what the wattage is when fully cranked, just for sh!ts and giggles!
Thanks Again,
Gene

[xtian]

No, your input signal should be in the range 0.1v to 1.0v, to simulate a guitar signal. Go ahead and try different frequencies. Won't make much difference within the amp's power band.

If you measure POST attenuator, you will be measuring the wattage...POST attenuator! If that's what you want to know, do it!

When fully cranked, you'll see the wave turn square, and approach full duty cycle. Max wattage will be about 2x clean wattage.

But, yes, do all of those things for yourself. First hand knowledge is best.

[xtian]

NB: watch the temperature on your dummy load!

[pdf64]

Note that for non-sine waves / overdriven sine wave signals, the meter will need to be a 'true rms' type for the measurement to be valid.

[The Ballzz]

Note that for non-sine waves / overdriven sine wave signals, the meter will need to be a 'true rms' type for the measurement to be valid.

Fluke 179. Close enough?

I thought humbuckers put out nearly 2.0v or so. Maybe it's just the drugs I did in the 60's & 70's &...........
Gene

[pdf64]

That looks nice http://en-us.fluke.com/products/digital ... meter.html

[The Ballzz]

That looks nice http://en-us.fluke.com/products/digital ... meter.html

Yeah,
I'm a tool junkie/whore! If I'm gonna use something more than twice, I get the "Good Stuff" but if it's for a job I'm sure I'll never do again, I'll buy the cheap, HF junk and suffer through till the job is done! With that said, I've had a few Harbor Freight "gems" that really surprised me, in a good way!
Thanks,
Gene

[xtian]

[I've had a few Harbor Freight "gems" that really surprised me, in a good way!

At the risk of 'jacking your own thread, do tell.

[The Ballzz]

Ha Ha, I'll Be Happy To Jack Away About Tools,

A) Their biggest "dust collector" for my woodworking that has served me well for over 10 years now. It REALLY sucks!
B) Their really cheap (sometimes on sale for $4.79 before the 20% off coupon) transparent yellow handled 4 piece wood chisel set. Takes a fantastic edge that you could shave with. Even if you only use them as gasket scrapers, TOTAL BARGAIN! In case you don't realize it, a "REALLY GOOD" single chisel can set you back $75-$80!
C) $30-$40, orange belt sander. the tracking doesn't start to mess up any sooner than the expensive ones, but even the expensive ones, once they start throwing belts, you're pretty much screwed so with the HF cheapie, you just toss it and get a new one! You can do that 3-5 times for the price of a "good" Makita, DeWalt or Porter Cable. Don't even get me started on Craftsman power/junk tools!
D) Their cheapest air powered die grinders and abrasive cut-off tools will last forever if you religiously oil them and keep the air inlet upright and capped when storing!
Just Sayin'
Gene

[eniam rognab]

i got a free tape measure, no purchase necessary

[Stevem]

What you will find as you check wave forms at lower frequencys is how the output power changes in accord with how well balanced the PI section is, as in phase canceling!
If a player is using drop tunings or a 7 string or greater axe , or Bass guitar this is something that should be looked at!

[Leo_Gnardo]

What you will find as you check wave forms at lower frequencys is how the output power changes in accord with how well balanced the PI section is, as in phase canceling!
If a player is using drop tunings or a 7 string or greater axe , or Bass guitar this is something that should be looked at!

True 'nuff and that's why I do my power testing at 200 or 100 or 50 Hz to see how loud & clean the low end will hold up. Cheap small amps, you don't expect good low frequency power response. Champs & similar, I test at 400 Hz, below that they can't sustain much power.

Ballzz yes you can get 2V out of a humbucker, if you twang the hell out of the strings. Tenth of a volt is plenty at the input of most any guitar or bass amp, when testing power it isn't a gain race. If an amp has fx send/return or pre out / power amp in, I'll send signal in there, bypassing preamp and all the noise & distortion it can bring, to find out if the power amp's working competently & give me a figure I can quote to the customer. Typically less than what the manufacturer says, measured at clip point. I suspect many manufacturers quote their power at 5 or 10 or 20% distortion, maybe more.

[The Ballzz]

Sincere thanks to all! You folks are fantastic and the answers are clear, concise and exactly what I was looking for!
Thanks Again,
Gene