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How many watts does an amp use?

#41
nashvillebill said:
FWIW, even Thomas Edison did not seem to grasp the mathematical relationship between power (Watts), current (Amps), and voltage potential (Volts) and their ties to resistance (Ohms). So he did not understand the inherent advantages offered by Tesla and Westinghouse's AC over his DC--that with AC, power could be distributed at high voltages (minimizing losses in the power lines) then brought back down to usable voltages with a simple transformer.

However, all three electrical pioneers could not compete with the financial clout of J.P. Morgan, who muscled his way into control of Edison'a patents and General Electric as well as control of Westinghouse and Tesla's work. I bet Edison wished Morgan could've been the first test subject of the Electric Chair :)
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Edison was a hack.
 
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#43
The VA rating of a transformer is only one factor of a design, primarily thermal. It means the core can support the flux at that power without saturating and remain under the thermal limits of the materials for a continuous application.

For amplifiers, continuous at full power is not necessary, and there are other design parameters that are far more important to the operation. For example the dynamic impedance, which governs voltage drop versus load. You can design a transformer that mimics a much larger transformer but doesn't have the continuous thermal capacity (or weight, or size, or cost). Since an amp operates between 1/8 and 1.0 x it's rated power (it does not operate continuously at 100% of bits rated power because music has to have a crest factor otherwise it would just be a tone) that must be factored into the equation. The safety agencies require the average power for thermal testing to be the minimum of 1/8 rated power or the average design power (which can be higher than 1/8)

This is a more complicated subject than it might seem on the surface.
 
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#44
ThisBass said:
With all supplies based on a line transformer. Why not read the sticker on the transformer? I think it's a good idea to start with the VA rating (power rating) of the line transformer itself.
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He is trying to determine the size of transformer he needs for the application. You don't want to buy a larger transformer than needed because they aren't cheap.
 
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#45
nashvillebill said:
FWIW, even Thomas Edison did not seem to grasp the mathematical relationship between power (Watts), current (Amps), and voltage potential (Volts) and their ties to resistance (Ohms). So he did not understand the inherent advantages offered by Tesla and Westinghouse's AC over his DC--that with AC, power could be distributed at high voltages (minimizing losses in the power lines) then brought back down to usable voltages with a simple transformer.

However, all three electrical pioneers could not compete with the financial clout of J.P. Morgan, who muscled his way into control of Edison'a patents and General Electric as well as control of Westinghouse and Tesla's work. I bet Edison wished Morgan could've been the first test subject of the Electric Chair :)
Click to expand...
Fun fact (that I never bothered to confirm): Edison originally wanted the electric chair to be named after Westinghouse.
 
#49
Yep. The idea was to start with the VA reading on the amplifier (line) transformer sticker (if present of course) once power stage topology is unknown. We all know that class H is more efficient than class A/B, and class D is more efficient than class H. So any estimation of a transformer based on the power amp output rating seems to be a crapshoot once topology of the amplifier is unknown.

As Andy allready mentioned the "strain" of the transforemer/supply isn't a steady number at "full", it's a number that varies with personal needs and, even at "full power" the strain of the supply depends on the crest of the signal. There are far to many influencies like playing style and sound settings and use of effect boards etc., this all in one of combinations possible makes a firm prediction like reading in a crystal ball.

I think 1/3 for average is not so bad to provide some power reserve for most of all applications.

Hope I don't cause to much of translation issues on a subject that is indeed more complicated than it looks like.
 
#50
Whippet said:
If an amp is rated at 400 watts at 4 ohms and 800 watts at 8 ohms, how big should my transformer be? is 400 and 800 the actual usage of watts or is the actual usage smaller?
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Bit of a nitpick, but it is unlikely to find an amp in the real world which puts out double the power into twice the load impedance. Guessing the OP meant the opposite... 800W/4Ω and 400W/8Ω. Even that is unlikely, as most amps do not double their output power into half the impedance....
 
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#53
sissy kathy said:
He is trying to determine the size of transformer he needs for the application. You don't want to buy a larger transformer than needed because they aren't cheap.
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It's not cheap for sure, but the weight is a even more problematic. Those things way a ton. And anything above 1500watts step down (230 input to 100 output) is considered industrial and the size is so huge you need a dolly. I had to carry the 1500 watt on the airplane, my god it was excruciating. Just that thing alone exceeded my carry on weight allowance. Thank god it was small that no one suspected how much it weighed.
 
#58
Whippet said:
Thanks for the reply. I had a feeling it was going to be as you said, consumption and output are totally different. For now I am using the Tec Amp Puma 900 and this thing as a voltage selector so it's no big deal but I am thinking of getting the Mark Bass Multi Amp which doesn't have the voltage selector. I might have to scrap this idea knowing that the step up transformer (115 to 230 volts) at 1500 watts usually weighs anywhere from 30 to 40 pounds and 1500 watts is probably not going to be enough.

Anyway thanks for the quick reply. Much appreciated.
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Whippet,
Your Tecamp has a voltage selector: use the amp made to make your life easy. Transformers are a royal PITA.
The Markbass Multiamp appears to have an internal voltage selector instead of an external switch. I learned this from reading the online user's manual.
If you are uncomfortable opening up the Markbass, get a tech to open it and change the setting for you.
 
#59
abarson said:
Whippet,
Your Tecamp has a voltage selector: use the amp made to make your life easy. Transformers are a royal PITA.
The Markbass Multiamp appears to have an internal voltage selector instead of an external switch. I learned this from reading the online user's manual.
If you are uncomfortable opening up the Markbass, get a tech to open it and change the setting for you.
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thanks for the reply. I sent a message to the guys at Mark Bass and they replied that I need a 600watt minimum. Now I'm not doubting the guys there but 600 for a 500 watt amp? From all the posts that I read, the majority say that you need a heck lot more than that. I am not at the liberty to check out the Mark Bass back panel since I am nowhere near any dealer so that will have to wait till mid January.

As for the internal voltage selector, I am surprised about this one because the site says that it's made for specific regions. Anyway I'll ask that once I am back in Japan when I can see one in person.

If all fails, I will stick to the Tec Amp, but as many would say, you just gotta have more toys! LOL All GAS aside, I know that Phil Jones comes with a different votage selector and so does TC electronics on some of their stuff. It limits my options for different amp heads but as you mentioned transformers are a headache.

Anyway thanks for the info once again.
 
#60
Mark Reccord said:
Oh, he tried. And succeeded. Killed lots of other animals as well. He actually tried to have "Westinghouse" made the official term for "electrocute." Edison was a dick.

Video is not for the faint of heart.
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what the fudge?! I know back then, they had different set of rules but come on! This is ridiculous. I did hear that Edison was a total dick but that just confirmed it.
 

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