Are there any special considerations measuring a Class D amps output power? Ive got a 700W (into 4 Ohms) Class D bass amp and I wanna check its output. I have a scope and 1000W 4 Ohm dummy load, to do so. When I measure clean power at clipping with a 1khz signal Like Inwoild with a tube amp I get 26VAC RMS. Thats just 169W. Am I missing something or do I need any special equipment to measure output power accurately with Class D?
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Measuring Class D output
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The load has no idea what kind of amplifier made the power.
Make and model of amp? Does it say 700wRMS into 4 ohms? or does it say something like peak power or music power?
700 watts into 4 ohms would need about 52v if I figure correctly.Education is what you're left with after you have forgotten what you have learned.
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Agree and add: HOW are you measuring those 26V RMS?
* With your scope?
Where do you clip hot and ground scope probe?
* With a hand held multimeter?
If so:
where do you put meter probes?
a) from speaker out Hot to ground
b) across load resistor, meaning black to one end, red to other end
I think whatīs hapening but donīt want to lead you, so please answer these questions first.
Of course now Enzo knows what I suspect, certainly others too, but please letīs wait for your answersJuan Manuel Fahey
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This is cruel. I only learned the answer recently, as I've spent the last decade learning tube amps, not solid state.
Cruel, I say.
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So this is the classic: "when is ground not ground?" Zen
or maybe the classic: "what is the sound of one ground clapping?" TaoIf it still won't get loud enough, it's probably broken. - Steve Conner
If the thing works, stop fixing it. - Enzo
We need more chaos in music, in art... I'm here to make it. - Justin Thomas
MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey
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Originally posted by Gaz View PostYou guys make my dumb questions more fun Ok I got 52V now measuring from across the dummy load instead of measuring from ground. Can someone explain?My band:- http://www.youtube.com/user/RedwingBand
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Yes, I wanted you to find it
Typical modern Class D amp architecture is bridged amps, donīt know why because itīs not really needed, I suspect snowflake "3.3V and 5V world" designers are *terrified* at dangerous high voltages ... such as 40V rails .... deadly 80V end to end and higher so they try to minimize that.
Going also to the extreme of using 2 ohm and even 1 ohm speakers (just check JBL EON and similar) so as to get high power with puny voltage.
So your 700W poweramp is *definitely* a bridged output one, so each speaker terminal, both "+" and "-" (canīt call it "ground" , can we?) swings 26V *relative to ground* and what you measured.
Since they are out of phase, you get full 52 V end to end, as predicted by Enzo.
Many go to an extreme trying to put scope across that floating output signal, from chopping Security Ground to try and get a differential front end (think old Tektronik and such) scope.
Me? ... I just conventionally scope one end to ground, and use my second scope channel to monitor the other.
Or even scope just *one* ... and then switch the clip and monitor the other, with scope ground clip staying where it belongs: ground.Juan Manuel Fahey
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Originally posted by J M Fahey View PostMany go to an extreme trying to put scope across that floating output signal, from chopping Security Ground to try and get a differential front end (think old Tektronik and such) scope.
Me? ... I just conventionally scope one end to ground, and use my second scope channel to monitor the other.
Or even scope just *one* ... and then switch the clip and monitor the other, with scope ground clip staying where it belongs: ground.
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Modern DSO scopes have differential mode.
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Originally posted by J M Fahey View PostYes, I wanted you to find it
Typical modern Class D amp architecture is bridged amps, donīt know why because itīs not really needed, I suspect snowflake "3.3V and 5V world" designers are *terrified* at dangerous high voltages ... such as 40V rails .... deadly 80V end to end and higher so they try to minimize that.
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