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Discussion Starter · #1 ·
I've been searching AVS and the internet for the last few hours and I can't seem to find anything that reliably answers the question of how output wattage relates to actually power consumption at the outlet. I've seen alot of forum posts and articles attempting to explain how the output wattage RMS is measured/distorted compared to the input, but nothing explaining to me how I can reliably predict power requirements.


I've recently been stationed overseas in Italy and my older Sony STR-K900 is on its way here. The specs sheet claims that it outputs 900 watts RMS, but at the same time claims only 170 watts of power consumption when operational. This doesn't make sense to me at all, and since its not dual voltage I need to make sure that I put it on a transformer that has sufficient output. And since I've been tempted to upgrade my receiver for awhile if I were able to find a dual voltage receiver (haven't looked yet, don't know if this even exists) I still need to understand how much power I'm drawing because of Italy's ****** power grid (I'm limited to 3000 Watts total load on my house, plus electricity is very expensive).


So long question made short, can someone help me understand power input vs output in the sense of worrying about getting an accurate consumption number versus the usual worry about getting as much power output as advertised?
 

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Short of measuring your actual usage with something like Kill-A-Watt, the rated power consumption on the back of the unit is the best number you're going to get. Get a transformer bigger than that. In fact unless there's a big difference in price you might as well get the biggest conversion transformer you can find. You might end up wanting to use it with something else.
 

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The mfrs. oftentimes claim peak output wattage capability, which an amplifier can produce due to energy storage like capacitors etc, in the power supply. For brief moments, generally enough to track a signal waveform transient, an amp can produce those peak figures. However if you saw the amount of power drawn over a 60hz circuit, the average amount would be less.


But, I'd caution you impeding your amps ability to deliver power by potentially choking off it's power supply with a transformer that's undersized. In audio, amplifiers rely of a breaker trip curve, of a normal wall circuit. This allows high amount of current to pass the breaker in the panel for brief amount of time. We generally only concern ourselves with subwoofer amplification, and the huge amount of power they need on short term basis. However, with a transformer between you and the breaker, a potential bottleneck occurs. So, I'd recommend getting a bigger Xfrmr, as apposed to a smaller one.


Most likely the 900 watt figure is un-necessary, however the 170 figure would be restrictive, ....I'd consider a 500 watt version, or equivalent.



Good luck
 

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Discussion Starter · #4 ·
Ya and I forgot I was looking at the receiver specs and the 200w of that 900w is the active sub which wouldn't be included in the 170. What sucks is that the transformers jump from 300w to 1000w at the PX and I already have a 300w that I just found out I don't need (apparently the ps3 slim is dual voltage despite the bottom plate only saying 120v).
 

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170W sounds very low. My amp puts out 110w per channel x 7 or 770w total, and the input is spec'd at 570W.


the Manufacturer would not have put in a bigger input transformer than what they think it needs, so 300W converter should be fine if the Manufacturer thinks it needed 170W. My guess is they were a little "generous" rating it at 900W output.
 

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I will tell you one thing...the specs are misleading. Without specific info, I can't tell you specifics. But if it's a 5.1 receiver that can put out 100 watts into 1 khz at 10% THD with only two channels driven, Sony will happily call that 500 watts right there, even though it's not really 500 watts.


That 170 watts is probably closer to accurate.


Receivers could draw more than rated power I believe. That's the unknown, for me.
 

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Discussion Starter · #7 ·

Quote:
Originally Posted by MichaelJHuman /forum/post/20794611


I will tell you one thing...the specs are misleading. Without specific info, I can't tell you specifics. But if it's a 5.1 receiver that can put out 100 watts into 1 khz at 10% THD with only two channels driven, Sony will happily call that 500 watts right there, even though it's not really 500 watts.


That 170 watts is probably closer to accurate.


Receivers could draw more than rated power I believe. That's the unknown, for me.

Ya I guess I'll give it a try when it gets here, I'm a little worried that with the active sub added in it will be too much but its not like I ever turn it up to max output levels. What signs should I look for to tell if my sub/receiver are getting under-powered and I need to get a bigger transformer?
 

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Quote:
Originally Posted by Jarmak /forum/post/20794744


What signs should I look for to tell if my sub/receiver are getting under-powered and I need to get a bigger transformer?

Either a fuse or some sort of protection device blows in the transformer, the receiver doesn't operate or the transformer gets very hot and may even start a fire.
 

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Discussion Starter · #10 ·

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Originally Posted by Ross Ridge /forum/post/20794895


Either a fuse or some sort of protection device blows in the transformer, the receiver doesn't operate or the transformer gets very hot and may even start a fire.

Oh so the receiver won't just get insufficient power from the transformer? it will actually overwork the transformer instead? Crap, that makes me not want to screw around with one that's possibly too small, I was expecting that my speakers/sub would just be under-driven.


Do they make dual voltage receivers or does the electrically sensitive nature of an amplifier make that impossible/prohibitively expensive?
 

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Quote:
Originally Posted by Jarmak /forum/post/20795080


Oh so the receiver won't just get insufficient power from the transformer? it will actually overwork the transformer instead? Crap, that makes me not want to screw around with one that's possibly too small, I was expecting that my speakers/sub would just be under-driven.


Do they make dual voltage receivers or does the electrically sensitive nature of an amplifier make that impossible/prohibitively expensive?

I seriously doubt the Xfmr doesn't have some measure of over-current protection. Cutting to the chase here; why don't you get the bigger one? Performance issues averted, over load issues averted. Done.
 

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Quote:
Originally Posted by Jarmak /forum/post/20795080


Do they make dual voltage receivers or does the electrically sensitive nature of an amplifier make that impossible/prohibitively expensive?

They do make dual voltage receivers, they essentially just have the tranformer built in. They might be not be easy to find, though. For example, Yamaha receivers are available in dual voltage versions, but I have no idea where you could get one. The receivers they sell in Europe and the US are all single voltage as far as I can tell.
 

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Discussion Starter · #14 ·

Quote:
Originally Posted by FOH /forum/post/20795294


I seriously doubt the Xfmr doesn't have some measure of over-current protection. Cutting to the chase here; why don't you get the bigger one? Performance issues averted, over load issues averted. Done.

I probably will, I was just trying to avoid spending the money on a 1kw transformer, or failing that put that money into an upgrade that would solve the problem (my original thought process pre-research was that mine Sony AVR wasn't dual voltage because it was old and a new ones would be).


I have been toying with the idea of upgrading my receiver for awhile now so I could get try HDMI fuctionality (the STR-K900 only has a pass through, I still have to use optical for the audio), plus if I got a 7.1 I could then upgrade the speakers later and have a 7.1 system (basicly replace my HITB piece by piece with better components). Also I've got my heart set on replacing my 46" Bravia with a top of the line 55"-60" 3D display when I get back from my next deployment and move back from the states, so I'll need to get something with HDMI 1.4 by then anyways. So the idea was instead of spending the money on a transformer just to make my current AVR run, invest that toward an upgrade that I'll need in the future anyway. But looking at this info I think I'm better getting a beefy transformer and just get what I'm sure will be a better unit for the same money 2-3 years down the road when I do the display.


I appreciate everyone's assistance on the matter.
 

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There might be issues with 60Hz AVRs running at 50Hz ac and lack of 50i video support. Some transformers have a loud hum. I personally would not bother bringing over an old AVR to a 50Hz country.
 
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