Hello guys,
I have just purchased that Logitech Z5500 sound system. I am trying it just now and I must say it sounds quite well. But I think that the producer of this equipment has invented a perpetum mobile. In user manual they say it has 500 Wats(RMS) of output power. But, next to the el. input socket on the rear panel of subwoofer there is written 230Volt / 1.5Amper and there is 2A fuse (european model). So 230x1.5=345 Wats of input power. So even if we admit 100percent of efficiency (common power amplifiers has about 60 percent), it must be a Perpetum Mobile :-)
Jarda

If I recall the schematic correctly, that fuse is not in the primary circuit. I remember seeing somewhere that the primary fuse was located inside the subwoofer, which I figured was a dumb way to do things, but then I discovered there are lots of electronc systems made this way. I guess they must figure if the load is severe enough to blow that internal fuse, you'll send it back to be repaired.

Come to think of it, one of my keyboards had three internal fuses, and one was actually soldered in place. Go figure!

If you have an ampmeter, you can plug the system into it and determine if it actually drawing 500 watts. I no longer have one of that capacity so I cannot help you there.

As for the sound, you've gotta' love it.

Cheers,

Gary

Hello Jarda, there are various possibilities to talk about power like musical power, sinus power or effective power. The sinus power means the peak-to-peak value. If you take this power (500 W) and divide the squareroot of 2 from it like this

500W / SQR(2),

then the effektive power is about 354 Watt.
It's not a 'perpetuum mobile' - it's the blind power of a magnetical spool captured and released by the pump effect of an electrical capacity.

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Greetings from Frankfurt (Germany),
Sheriff ;-)

[This message has been edited by Sheriff (edited 02-25-2005).]

Couldn't have put it better myself Sheriff !!!

KF

Hmm... gravedigger said RMS power is 500W; not peak power which is 1000W for this system. So, why divide RMS power by Sqrt[2]?

Shiral

Well guys, I dont think that 500 watts output power has anything to do with the input voltage. I have a 400 watt amp in my car and it is running off 12v. If I understand this. he said the docs claim 500 watts (rms) but is confused about the input voltage. What ever is inside the woofer(power amp) will decide rms no matter what is feeding it. just my opinion.

the 1.5 amp will be the draw from wall outlet.

Hi Guys:
From the logitech z5500 owners manual

Total peak power: 1010 Watts
Satellites: 317watts Rms (2x62W front,2x62W rear,69W center
Subwoofer: 188Watts
Total rms power: 505 watts Rms

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Cheers....Pose

Thanks loungelyzard for the exact numbers.

Power consumption depends on both supply voltage and the current the unit draws. Even if you apply only 12V the unit can draw big enough a current to suck in whatever power it has to consume. Also, a unit cannot produce more energy than it consumes unless there is a chemical or nuclear process that emits energy is going on inside of it which is not the case for these units. These numbers looks a bit odd to me too.

Shiral

A few months ago, I posted Ohm's Law, which essentualy provided the formula for calculating power in watts, resistance, etc. It's not a complex calculation, but in this case, you must know where in the circuitry the fuse is located. If the fuse is in the AC line, then the system is obviously not 500 watts RMS--not possible. However, if the fuse is situated farther down the line in the circuitry, then it is possible. In many instances, there are heavy-duty, automatic-resetting, internal circuit breakers that take care of the AC line and are placed in front of the power transformer's primary winding. Secondary fuses are then placed beyond that point to protect more delicate segments of the system. Years ago, I had an 8 channel preamp that had a fuse for every channel. The fuse was very light and only protected that channel--not the total pre-amp.

For those who cannot remember the formula for calculating watts, print this out: Power in watts for alternating current is P=EI where E and I are the electromotive values expressed in volts and amperes respectively.

Calculating power for direct current (DC) circuits is a bit more complex, and the formula is P=EI=R1. The power in watts developed by an electric current flowing in a conductor, where E is the diffeence of tpotential at its terminals in volts, R its resistance in ohms, and I the current in amperes.

Now, lets get to the crux of the matter. How does the amp sound to you? If it sounds clear, crisp, clean and seems louder than your old 300-watt brand-X amp, then that's all that really counts.

Cheers,

Gary

Thanks Gary! That makes sense.



I think this should be P=EI=RI^2 (because E=IR)



I agree, that's all I would care about after buying the system. But when shopping for a system or deciding what system to use where it helps to understand how different systems have been rated.

Thanks
Shiral

I think this should be P=EI=RI^2 (because E=IR)

Yes, you are correct. I neglected to type the final segment of the formula.

Must be gettin' old,

Gary

I guess that value results by the stereo effect. -> 2 times 500 watts = 1000 Watts <-
In this case there should be a 2nd fuse somewhere else inside the case.
Imho RMS is a non-related term in electrical engineering. I've only heard about it in combination with master recording (this means tone engineering).

Otherwise the inner circuit for example with 12 volts and 1.5 amps will supply only 18 watts. The same fuse in AC circuit will supply 230 volts x 1.5 amps = 345 watts.
Now calculate 345 watts x SQR(2) to get peak-to-peak power of 487.9 watts!
If you'd round up this value then you'll get the 500 watts which Jarda has written.

The last remaining point I'm thinking about is the manual. Some manufacturers do really write nonsens!!!

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Greetings from Frankfurt (Germany), Sheriff

[This message has been edited by Sheriff (edited 03-09-2005).]