THE ALL CHANNELS DRIVEN FALLACY

[Buckeyefan 1]

Yes, but in 2 channel it is barely above its 5 channel rating. So much for being a better amp when those conditions would never come.

Wait just a second. Notice the relationship between the 4 ohm and 8 ohm ratings:

By 2 channel output into 8 ohms at 0.1% THD:
Denon (132.2W), Pioneer (121.2W), Yammie (102.9W), HK (84.6W)

By 2 channel output into 4 ohms at 0.1% THD:
Denon (218.4W), Pioneer (197W), Yammie (158.4W), HK (146.9W)

The HK is the best of the bunch that comes closest to doubling it's power when resistance is halved. I never said these receivers were on a level playing field, but it appears the "less stout" HK is showing off in 4 ohm load, even though its 8 ohm load doesn't seem to match the others.

It could be current limiting, but it also could be that HK built the unit to withstand tougher, more demanding speakers with a robust power supply and larger heat sink.

 

[race4aliving]

Nice budget. If you don't go the power amp route, this may suffice.

http://www.audioweb.com/Ad/AdInfo.asp?adid=157782

I think this might end up selling for alot more then $3500.00 budget. I know on a couple of the other auction sites that I have a bit more trust in, the Lexicon RV8's range in price from $5200. to $6000.

 

[thxgoon]

And you arrived at this how? Famous last words, 'trust me.' Why should anyone trust you?

I arrived at this how? Hmm, I heard it! In my own living room.

Excuse me for offering my personal experience without the stamp of a notary public and a S/N chart. Good lord.

 

[PENG]

Fair enough. It appears the HK is the loser at first sight. But is it?

It's the only receiver to claim 75 watts per channel, when in reality, is putting out a bit more (in all 5 channels). Kudos for honesty to HK.

[/B]

Agree, but while not a loser, the 630 does sell for about the same as, or more money than the others, yet offer less power output. Aside from being honest, they don't necessarily give more value for the price. The AVR7300 is a different story, definitely one of the best value as long as you are in the U.S.

 

[Buckeyefan 1]

Agree, but while not a loser, the 630 does sell for about the same as, or more money than the others, yet offer less power output. Aside from being honest, they don't necessarily give more value for the price. The AVR7300 is a different story, definitely one of the best value as long as you are in the U.S.

Good point. HK is definitely not known for being the "Pioneer 1015" of the bunch. You pay a bit of a retail premium for the name.

But street prices are much more favorable than the Denon 3805 or Yamaha 2500, especially with on line dealers. HK offers the best warranty of the bunch from their ebay store on "B" units, and have an outstanding customer service department. You can purchase a 630/635 normally under $500 at Harmans ebay store (1yr warranty), while the Denon rarely goes for less than $735 (90 day warranty) on places like Ubid - and that deal only shows up once in a blue moon.

Try finding a 2500 for <$500 - with any warranty. The Pioneer Elite 52/1015 are simply great buys (just like the HK7200/7300). I have no argument there. I think with HK, you are paying for excellent service, a well built beefy unit, and honest claims of power output (which is my issue on this thread).

 

[Buckeyefan 1]

Here's another case in point. Take Best Buy's audio all in one packages. They (fault BB for this one) are taking the watts per channel, and multiplying it by the number of channels. Then, to make matters worse, they add the peak power rating of the subwoofer, then tout that system as having available those total watts. This IMO is unacceptable.

www.bestbuy.com/site/olspage.jsp?type=category&id=pcmcat17700050110

Example laid out below:
Yamaha/Klipsch Synergy III 1,630W 5.1-Ch. Premium Audio Cinema System

Front Surround Power per Channel 140W x 3
Rear Surround Power per Channel 140W x 4
650-watt 12" sub
So 140W x 7 = 980 + 650 watt sub = 1630.

Perfect.

 

[DaveOCP]

I think part of the problem is there's a different standard for receivers and power amplifiers. When somebody like Krell, Parasound, etc says 200W X 5, thats exactly what they mean. It will do 200W into 5 channels at once without clipping or even creating much in the way of THD at all.

Certain receivers may say 140W X 7, but that does not mean driving all channels. It means it can output 140W to one channel without clipping, and it is capable of driving 7 channels to some unspecified power level. I dont think thats honest. Its certainly not nearly as bad as the "P.M.P.O" on junk electronics which is a total lie, but it is at least misleading.

If its OK for receivers to rate their power that way, then it should be OK for Krell to list their amp as 350W X 5 because it is capable of driving one channel to 350W without clipping. Rather, I think receivers should be forced to follow the power amp standard. Some, like HK and Denon, do. Yamaha does not.

 

[MDS]

Same old debate with the same old arguments...

Taking the all channels driven tests at face value despite their obvious flaws, which would you rather have:

H/K rated 50 watts per channel and produces 50 wpc when driving 1, 2, or N channels.

vs

Denon/Yamaha/Onkyo/et al rated 100 wpc and produces substantially more than 100 wpc into 2 channels but only 50 wpc into N channels.

On dynamic material, the latter group will deliver far more power.

 

[gene]

I think part of the problem is there's a different standard for receivers and power amplifiers. When somebody like Krell, Parasound, etc says 200W X 5, thats exactly what they mean. It will do 200W into 5 channels at once without clipping or even creating much in the way of THD at all.

Sorry but your are way off on that one. All of the Krells and Parasound amps I am aware of utilize a single power cord and a linear amp design. Best case scenario for linear amp designs factoring in very conservative power factor and transformer losses and you are lucky to get 40% efficiency. Lets do some remedial math.

200wpc x 5 = 1000 watts / .4 = 2500 watts. If the amp adheres to IEC standards, then the power recepticle is limited to 15A to prevent arching. 15 * 120 = 1800 watts. So now you are 700 watts shy of sourcing enough power to meet the precious ALL CHANNELS DRIVEN TEST. The best case scenario for a linear amp with one power cord and one wall outlet is roughly 144wpc x 5 ALL CHANNELS DRIVEN (assuming no external line regulation is used).

What is even more entertaining is when these amp designs claim to double down power with all channels driven. Lets use Parasound as example. Their 5CH amp claims 400wpc x 5 all channels driven.

http://www.parasound.com/halonew/A51details.php

hmm. One power cord, linear amp.

Let's see:
400x5 = 2000 / .4 = 5000 watts! You would need 2 dedicated 20 amp circuits to do this. But wait, they are only using a 2.2KVA transformer? Hmm so even if we did have 2 dedicated 20amp outlets, ignored the IEC 15A limitation, we need a transformer with at least 30% more capability because their current transfomer is incapable of delivering this much power continuously to all channels.

I suppose since this is a $4k Separates product, people don't hold the same critiques on their power claims like they do with a $1k receiver

PS. Note that Krell never claims their 5CH amp power spec is with ALL CHANNELS DRIVEN. Instead they rate power for EACH channel driven. Hmm looks like they designed one dynamic amp that can swing alot of power to EACH channel when needed.

If you look at their max power rating of 2500 watts, this assumes you have a dedicated 20amp line of course, this amp may deliver near 200 wpc x 5 ALL CHANNELS assuming the line voltage is held constant and the transformer doesn't saturate. But into 4 ohms it CANNOT deliver 400wpc x 5 continuously.

http://www.krellonline.com/html/m_KAV_p_TAS_spec.html
note again 1 power cord

 

[thxgoon]

PS. Note that Krell never claims their 5CH amp power spec is with ALL CHANNELS DRIVEN. Instead they rate power for EACH channel driven. Hmm looks like they designed one dynamic amp that can swing alot of power to EACH channel when needed.

Not to nitpcik, but Krell also makes an amp with 125W/Ch. That's not 'huge' dynamic power, but it sounds freaking incredible when you push it hard. And within it's transformer size and fuse rating (also the halo A-52) it is capable of all channels driven. Sunfire claims that their Signiture Seven channel amp is capable of 400 watts all channels driven, but there is no way they can pull that much from one socket, even with their great efficiency.

If anyone has ever watched a power conditioner with a current draw readout while cranking their favorite movies or music, they've seen what I have. As loud as my ears can tollerate, running 4 ohms speakers and listening to DVDA or a loud surround fest using all channels as much as possible, I've never seen more than about 5 amps pulled from the wall. 5*120=600Watts usage. Factoring in the 40% efficiency, that's 240Watts distributed to each speaker. Lest than 50W/Ch. And thats freaking LOUD! Typically speaking though, when running at 50W/Ch, a better amp with a better power suply handles this with more finesse. Using the 'all channels driven' test is perhaps the only clue a net surfer will ever get as to what's under the hood. Like car horsepower. A 190HP sedan is as quick to 60mph as a 220 hp turbo charged coupe. HP doesn't say everything but it at least serves as an indication of the cars capabilities. You'll rarely if ever use 500 horsepower out of the new M5 (drool) but you know when you are passing at 55 MPH at 6000 feet in the mountains (where it can't create full power) you'll have no problem with the maneuver.

I think someone said it best when they said best buy and cheap htib's are to blame for claiming rediculous power by multiplying single channel power by number of channels. I wish there were standards these companys had to comply to on things like this.

 

[gene]

thxgoon;

Not to nitpcik, but Krell also makes an amp with 125W/Ch. That's not 'huge' dynamic power, but it sounds freaking incredible when you push it hard.

Ok, but what does that have to do with my previous post showing that very few amplifiers (separates included) can meet full power under this type of test scenario? I never even discussed sonic attributes.

The truth of the matter is an absolute power rating of an amp, just like HP in a car, tells very little on how it will perform sonically. This is why we put more resources into testing other metrics that really do matter. People get too hung up on power, not even realizing the rated power specs are very conditional, and that the wall outlet is usually the limiting factor, not necessarily the amplifiers output power capability.

The reasons people may prefer a high end Parasound/Krell/separates amp over the amp section in a $1k receiver are:
1) The separate amp has a lower and more uniform output impedance. The advantages here is it will sound more consistant when driving an assortment of loudspeakers regardless of their impedance/phase profile.
2) The separate amp is more capable of driving reactive speaker loads undistorted and unadulterated partly b/c of reason#1 and because of a beefier power supply, more heatsink area, and more output devices.
3) The amp will not have nearly as much frequency response variation as the $1k receiver amp based on #1 and #2.
4) The amp has less slew induced distortion, particularly at high frequencies when driving reactive loads.
5) The amp has more phase margin allowing it to drive reactive loads more easily.
6) The amp likely has better power supply filtering and noise immunity.

Really all 6 of these are interrelated.

I think someone said it best when they said best buy and cheap htib's are to blame for claiming rediculous power by multiplying single channel power by number of channels. I wish there were standards these companys had to comply to on things like this.

I agree, but realize the people they are being marketed to. Most folks buying HTIB systems could care less about accurate power ratings. They want a big # to impress their friends. Power in general is greatly inflated as you have seen in your power consumption test mentioned here.

Actually I believe the FTC is working on a multichannel white noise test with a variable duty cycle per channel, perhaps similar to what THX does. I know someone who is on the committee and I will check back with him.

 

[Buckeyefan 1]

I may join this committee. I agree there's a limit to how much power an amp can put out, but I don't agree on the tactics manufacturers as well as retailers use to sell these units. You just don't add up watts times channels, then add subwoofer peak output to sell a HTIB. BB should be fined.

http://members.ce.org/standards/CommitteeDetails.aspx?Id=000011021815

http://members.ce.org/standards/GetInvolvedJoin.aspx

 

[thxgoon]

Ok, but what does that have to do with my previous post showing that very few amplifiers (separates included) can meet full power under this type of test scenario? I never even discussed sonic attributes.

Gene, I'm not trying to argue with you. I'm simply trying to say that 'all channels driven' serves as an indication, of what's underneath. Nothing more.

My point in using the Krell 125 watt amp is that it doesn't have a large dynamic power p/ch but still maintains a great sound quality. Granted there are more than a few reasons for this but you mentioned that you'd rather have a large dynamic power to one channel as that is more real world. You mentioned that on a 130 Watt amp. Here the Krell is 125 Watts, and sounds better when cranked with less dynamic power. So neither dynamic power nor all channels power mean much when it comes to sound quality. But an amplifiers power supply does play a large part. Generally, a better amp will have a better power supply and a better power supply will provide more output power all together thus (at least partially) validating an all channels driven test. Granted to be fully acurate the test would have to take place under exact conditions for all amps involved and each amp must be qualified for line usage. However, most car horsepower are rated in much the same shady fashion, but that doesn't mean that a 500 horse car won't smoke its tires even if it really can't produce that much for an extended time with the muffler, air filter, and computer in place. I'm mearly stating my opinion from experience in that listening to amps with better power supplies sound better, and you can't deny that 'all channels driven' is somewhat indicitive of the size and capability of the power supply. Whew. In a perfect world we'd all get to listen to every amp and see skematic diagrams before ever purchasing one, but that just isn't the way it is.

 

[gene]

My point in using the Krell 125 watt amp is that it doesn't have a large dynamic power p/ch but still maintains a great sound quality.

Actually dynamic power is relevant to sound quality. The Krell amp you are so fond of likely has alot of overhead past its 125wpc rating, especially when driving low impedance loads. Again, see my post above for other reasoning. Regardless, this thread was not discussing sound quality as much as the validity of a very conditional and unrealistic test (that isn't followed as consistantly as it should be) as well as the reasoning why some amplifiers don't do well with these tests b/c their design goal is to deliver real world dynamic range in an economical package.

 

[thxgoon]

The Krell amp you are so fond of

I was merely using it as an example.

So, now that my wheels are turning, why would a company like Krell or Parasound underate their amps? A review on the A-52 found that it could put out over 170 Watts continuously into 2 channels at 8 ohms. Why not rate their amp at 170W/Ch? Same with the Krell?

 

[majorloser]

I remember long ago when a HK regional sales manager once told me that their amp was rated with lower wattage but put out higher amperage.

Obviously he never heard of Ohms law.

Like all consumer electronics, audio equipment is hyped up and it takes us comsumers to study the independent testing to come to our own conclusions. Sources, such as this thread, are how we as consumers learn what to look for in a product.

It would be nice if all manufactures used the same methods of testing and comparison.

But a saleshole is a saleshole........

Caveat Emptor

 

[Audioholics]

Just to chime in here... One thing we want our readers to understand is that if you harp so much on power - to the exclusion of nearly everything else - manufacturers will eventually cater to you as well (just like they do to the BB/CC crowd).

The end result could be very powerful amps that pass a non-realistic test scenario with flying colors while simultaneously bombing the more important metrics. There are new amps coming out soon (and even now) that will attain to even higher power levels. If all you care about is power - you may quickly lose track of how to best compare products.

We're not trying to be combative or defensive - we're trying to keep everyone in perspective and continue to "pursue the truth" on this issue.

 

[thxgoon]

Actually I believe the FTC is working on a multichannel white noise test with a variable duty cycle per channel, perhaps similar to what THX does. I know someone who is on the committee and I will check back with him.

It would be great to hear what you find out.

 

[PENG]

I remember long ago when a HK regional sales manager once told me that their amp was rated with lower wattage but put out higher amperage.

Obviously he never heard of Ohms law.

[/B]

The HKAVR7200 used to be my dream receiver, but you're so right about this high current thing. I have read posts after posts that show how many people were misled to believe a low output receiver can put out high currents, and they would say "its not the watt, but current that counts".

In fact, HK's has always been careful (or honest) about their high current claims. They always add the word "instantaneous", to make it clear that they are capable of high currents such as 75A for their flag ship units, for a very short duration. Also, it is 75A at the output, i.e., much lower voltage. Refer this current back to the 120V a.c. side, you may see less than half that, and again, only for a fraction of a second; if there is a demand for it at all.

 

[PENG]

Sorry but your are way off on that one. All of the Krells and Parasound amps I am aware of utilize a single power cord and a linear amp design. Best case scenario for linear amp designs factoring in very conservative power factor and transformer losses and you are lucky to get 40% efficiency. Lets do some remedial math.

200wpc x 5 = 1000 watts / .4 = 2500 watts. If the amp adheres to IEC standards, then the power recepticle is limited to 15A to prevent arching. 15 * 120 = 1800 watts. So now you are 700 watts shy of sourcing enough power to meet the precious ALL CHANNELS DRIVEN TEST. The best case scenario for a linear amp with one power cord and one wall outlet is roughly 144wpc x 5 ALL CHANNELS DRIVEN (assuming no external line regulation is used).

What is even more entertaining is when these amp designs claim to double down power with all channels driven. Lets use Parasound as example. Their 5CH amp claims 400wpc x 5 all channels driven.

http://www.parasound.com/halonew/A51details.php

hmm. One power cord, linear amp.

Let's see:
400x5 = 2000 / .4 = 5000 watts! You would need 2 dedicated 20 amp circuits to do this. But wait, they are only using a 2.2KVA transformer? Hmm so even if we did have 2 dedicated 20amp outlets, ignored the IEC 15A limitation, we need a transformer with at least 30% more capability because their current transfomer is incapable of delivering this much power continuously to all channels.

I suppose since this is a $4k Separates product, people don't hold the same critiques on their power claims like they do with a $1k receiver

PS. Note that Krell never claims their 5CH amp power spec is with ALL CHANNELS DRIVEN. Instead they rate power for EACH channel driven. Hmm looks like they designed one dynamic amp that can swing alot of power to EACH channel when needed.

If you look at their max power rating of 2500 watts, this assumes you have a dedicated 20amp line of course, this amp may deliver near 200 wpc x 5 ALL CHANNELS assuming the line voltage is held constant and the transformer doesn't saturate. But into 4 ohms it CANNOT deliver 400wpc x 5 continuously.

http://www.krellonline.com/html/m_KAV_p_TAS_spec.html
note again 1 power cord

Gene, many thanks for finally taking the time to explain the theory behind this topic so thoroughly and clearly. The only thing I am not sure if you are 100% right is the 40% efficiency you assume. I thought it varies between different designs. It could be lower than 40%, as you had hinted, but it could also be higher than 50% in some rare cases, no? I am not an audio engineer, its just my educated guess at best.