o2bfit Posted February 13, 2004 Posted February 13, 2004 Hello All, I was reading a review of some receivers on www.homecinemachoice.com that as part of the review tested the rated output and actual output. I was surprised (shocked at Denon) to see a drop in the output power when some of the receivers were put in 5.1 channel mode into 8 ohms. Typical Outputs were: - Denon AVR1804 (2 channel - 110W, 5 channel - 35W) - Denon AVR1803 (2 channel - 110W, 5 channel - 45W) - Denon AVR3803 (2 channel - 130W, 5 channel - 50W) - JVC RS-8032VSX (2 channel - 100W, 5 channel - 20W) - Marantz SR4400 (2 channel - 110W, 5 channel - 85W) - Marantz SR5400 (2 channel - 110W, 5 channel - 85W) - Onkyo TX-SR501 (2 channel - 80W, 5 channel - 35W) - Onkyo TX-SR701E (2 channel - 120W, 5 channel - 50W) - Sony STR-DB790 (2 channel - 96W, 5 channel - 65W) - Pioneer VXS-D912-S (2 channel - 90W, 5 channel - 80W) - Yamaha DSP-AX640SE (2 channel - 105W, 5 channel - 39W) All of the receivers met or bettered the rated two channel output, so it appears that some of the receivers power supplies are unable provide enough current. I'm not saying the power output is anyway related to quality but it does limit what full range speakers in 5.1 you can effectively drive. How do some of the owners of some of receivers that had massive power drops feel about this? Regards
Michael Jones Posted February 13, 2004 Posted February 13, 2004 Originally posted by o2bfit I was reading a review of some receivers on www.homecinemachoice.com that as part of the review tested the rated output and actual output. I was surprised (shocked at Denon) to see a drop in the output power when some of the receivers were put in 5.1 channel mode into 8 ohms. The dirty secret of many AV receivers! First, a little clarification. Take a 80W AV receiver, that is rated at 80W x 5 channels. Each channel can and will produce 80W individually. But each channel will not produce 80W while the other channels are producing 80W. The figure in the posting above will be the maximum power from each channel while the other channels are also producing maximum power. It shows that the power supply sags when producing high power into all channels at once. In the real world, high power into all five channels at once is extremely rare. Some of the examples above aren't as bad as they may initially appear. For instance, the Marantz SR5400 has a rated power output of 90W/ch into 8 ohms. That it produces 85W/ch into all five channels at once suggests that its power supply is pretty good. The good power supply is probably one reason why the x300 and x400 range of Marantz AV receivers have developed such a good reputation for sound quality. Not all manufacturers are disingenious with power ratings. NAD, for example, rate their AV receivers with all channels powered. Again, a good power supply is one reason for the superb sound on NAD AV receivers.
o2bfit Posted February 13, 2004 Author Posted February 13, 2004 Its a little comforting to me that I bought a Marantz. I was very surprised at the Denon's performance. The AVR1804 apparently had an improved power supply which is supposed to allow it supply more current. But at 45W, it would be better suited for a sub/sat setup or use efficient speakers. I thought it might have been a low end receiver problem but the AVR3803 has it as well. Its a perfect example that you can't rely on manufacturer specifications.
Michael Jones Posted February 13, 2004 Posted February 13, 2004 Originally posted by o2bfit Its a perfect example that you can't rely on manufacturer specifications. You can rely on the specification, it's just that the spec may not mean what you think it does. Back in the 1970s a number of amplifier manufacturers were being a little imaginative with their power ratings. The Federal Trade Commission (FTC) in the United States mandated a way to specify power rating in a more real way. So a stereo amp with a power rating of X watts per channel into Y ohms at Z distortion should meet the FTC specs. However that specification doesn't apply to multi-channel amps. But a 100wpc AV receiver will put out 100W, just not neccesarily into all channels at the same time.
Jonr Posted February 13, 2004 Posted February 13, 2004 My understanding is that there is no set way for the power rating to be declared. I have seen this discussion many times with many folks who accuse Yamaha and others of out and out lying. I do think that their rating is misleading as opposed to NAD and others. What I don't understand is that in the reviews of these av receivers, this rating discrepancy is noted in an inset box but then almost ignored or never discussed. In fact, I have seen reviews which have the ratings all channels driven as 39 and then in the body of the review, the reviewer will refer to the receiver as a powerful 100 x 5 receiver. Maybe someone can explain why that is done as well as certain receivers are reviewed instantly and almost always favorably whereas other receivers may be never reviewed? Is there too much nepotism between the manufacturers and the reviewers?
Michael Jones Posted February 13, 2004 Posted February 13, 2004 Originally posted by Jonr Maybe someone can explain why that is done as well as certain receivers are reviewed instantly and almost always favorably whereas other receivers may be never reviewed? Is there too much nepotism between the manufacturers and the reviewers? You're welcome to start a thread about another topic, but please keep an existing thread on its original topic.
o2bfit Posted February 13, 2004 Author Posted February 13, 2004 Originally posted by AudioEnz However that specification doesn't apply to multi-channel amps. But a 100wpc AV receiver will put out 100W, just not neccesarily into all channels at the same time. I guess it comes down to interpretation then. When I read a specification and it says "100W x 5 all discrete Amplifier Channels", I interpret that it can produce this power all at once. I don't read it as each of the channels can produce this power just not at the same time. The manufacturers don't exactly point this clause out.
michaelw Posted February 13, 2004 Posted February 13, 2004 One key specification missing from many spec sheets is the size of the power transformers used. Transformers are measured in VA (volts ampere). According to Ohm's Law 1 VA = 1 watt. Therefore if you know the size of the transformer you will have an idea of what the amp can really output. Eg. your 100x5 AVR would need a 500VA transformer to meet it's specified power. Occassionally you get a freak amp like the K... that can handily exceed the output implied by transformer size through the use of a highly regulated power supply. If you push a transformer really hard it will keep delivering more power but at poorer regulation. Variations on Ohm's Law tell us that an amp's 8 ohm power rating should double into 4 ohms. If it doesn't it implies some current limiting or with AVR's, problems in keeping heat buildup under control. That's why many AVRs have 8/4 ohm switches on the back, a method of self preservation. A second variation on Ohm sez that as impedance halves, current should double but only if the power supply can deliver and if the output devices can carry twice the current.
GraemeWi Posted February 13, 2004 Posted February 13, 2004 I've got a Denon 1803 and have to say that sure on paper it doesn't deliver but watching a typical DVD there are not all that many scenes where all speakers are pumping at the same time. Of course someone will pull out Swordfish and play the first scene, but there is far more to watching DVDs than just the first scene from Swordfish. Cheers, G
Mycenius Posted February 13, 2004 Posted February 13, 2004 Originally posted by michael w Variations on Ohm's Law tell us that an amp's 8 ohm power rating should double into 4 ohms. If it doesn't it implies some current limiting or with AVR's, problems in keeping heat buildup under control. Indeed - Quite common on newer amps from what I've seen. Example the Plinius 9100 only goes from 120W to 180W, the Plinius 9200, Perreaux 200i, Musical Fidelity A308 all go from 200W to 300W+ approx. It seems pretty common for modern amps (at least stereo ones) to only increase output by 50% when impedance is halved - presumably a sign of significant "current limiting" or "heat issues" or similar in the construction... Just out of interest the Perreaux E160i starts at 160W at 8 ohms and only increases by 25% to 200W approx when the impedance is halved to 4 ohms. It's a different story on the AVR front of course, the Denon 3803 rated at 110W pc at 8 ohms only increases to 150W pc at 4 ohms - only about a 35% increase without considering the issues of real output on 5 channels at once (as O2bfit posted above)... Pity they didn't repeat those tests into 5 channels at 4 ohms to see how much variation there was? M.
Coops1553552671 Posted February 13, 2004 Posted February 13, 2004 "Of course someone will pull out Swordfish and play the first scene, but there is far more to watching DVDs than just the first scene from Swordfish." Exactly, the occasions in movies where all 5 channels will be called upon to deliver full power are very very few & far between .... the swordfish scene being the most taxing I can think of. However, one thing to bare in mind is that HT is simply "the illusion of movement through sound". This means that the 5 channels swing the sound from one channel / speaker to another, meaning that 99% of the time there are probably no more than 2 channels being severely taxed at one time. Even that scene from Swordfish ... the sound is swung around the room cyclone like, meaning that as the sound is transferred from one to another the strain would be kept on 2 possibly 3 channels most of the time. We demo THAT scene often (mostly because it is a reference scene demoed by every other shop too, I'm wholly sick of it) & the Yamaha amps breeze through it, as do the NAD's. Even at pretty excessive volumes (people will often demo gear a hell of a lot louder than they'll ever use or be allowed to use it) both brands maintain composure for the 20 secs or so. Using Proac speakers at 86db efficientcy made one of the Yamaha 740's shut down once & go into protection mode, but really that was a case of towing a 3 horse float with a Toyota Starlet ... $20,000 worth, across the front 3 of 86db efficient speakers that are normally powered with big Plinius amps & the like, and all that happened was the amp simply clicked off. We turned it back on 30 secs later & its never missed a beat since. I don't think its anything to get too upset about :cool:
Max Christoffersen Posted February 13, 2004 Posted February 13, 2004 One specification that is often overlooked is current draw - it'll be on the back of the amplfier or in the Manual somewhere. This may be a more real world indicator of performance. What goes in comes out. In this discussion I don't think anyone has actually used the amplifier specification correctly - it is always tied to frequency spread 20-20 - if it isn't they're cheating. Max Christoffersen
steverb Posted February 14, 2004 Posted February 14, 2004 Onkyo TX-SR600 The shop had it listed as 125W RMS all channels & confirmed this when I asked I knew this was BS. Even the manual says 80W (from memory) & I knew it was tested at around 40ish. Bought it anyway (price was right, HT only, I have anotehr setup to play CD's) an 80W amp needs aapprox a 140W VA transformer.(mine was a 6 channel amp) In new from the weight & the size of the transformer it wasnt the necessary 700-800+ VA. But if you actually measure power output during normal use (ie no blood dripping from ears) you will see even loud volume in a normal sized room is less than 10W per channel. Do some math (db,logs etc) you will see that to DOUBLE the sound volume you need around 10x power increase (asuming you have perfect speakers) Even seen a speaker lasting with a true 100W continous for extended periods of time?? They wont sound the same at this volume either. But still, lies are lies, and hifi shops that DO know better shouldnt be repeating them
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