[skrivis]

FrankVanA made clear that this product could not work as stated on a standard 120VAC outlet. Would a 1500W hairdryer also not work when plugged into the same outlet as it presents a continuous draw, not peak?

There is no reason to disbelieve that a product rated @ 125W x 7 could not work as stated unless either of you have measured it and verified that it does not meet it's specification. If so, please post your findings.

speaker

It's simply impossible. Do the math.

[Dan Banquer]

Actually I think most of you are pretty well conditioned to looking at linear amps and supplies and the resultant efficency or lack there of as the case may be.
When you initially think about switching amps and suppiles you need to think of the conversion of watts to watts. A 20 amp household line is capable of doing about 2,000 watts realistically. The switcher in question here is rated at 7 channels at 125 watts into 8 ohms. Given the efficency of switchers vs. Class AB The switcher in question appears to be specified for about one half the power of the 20 amp line. Note switching power supplies can have an efficency of anywhere from 60% to 90% depending on the type of design, and the amps in question are rated at 93%. In short; yes it's possible to drive 7 channels at 125 watts per channel into 8 ohms. No it does not say anything about the quality of power.
             d.b.
P.S. Frank; your numbers look pretty much correct for linear amps. In fact I'm in the process of doing an article for Audioholics and your numbers are very close to what Gene and I are seeing as possible for linear amps and linear supplies. Thanks for the confirmation.

[DVV]

Lets try again with a little basic electrical math  (no fun at all of course).

True RMS power equals [(peak voltage swing times .707) squared] divided by load resistance.  For example, a Fet Valve 350EXR swings about plus and minus 66 volts into 8 ohms (both channels driven).  The RMS power then is (65 x .707) squared, quantity divided by eight equals 272 watts per channel into 8 ohms, both channels driven.  Current equals RMS voltage divided by load resistance which equals about 5.8 amps of current thru ...

Not arguing with your math, Frank, but I don't think it works quite that way.

My lab experience with multi-channel receivers is hardly extensive, but I did have a few facing the works. And in all instances, they did deliver their rated power outputs in classic terms into 8 ohm loads in the usual FTC manner, you know, xx watts into 8 ohms, 20Hz-20kHz, at rated distortion or below. They delivered into 6 ohms as specified as well, probably because of the THX rating requirements. One was rated at 100W/8ohms, and it delivered +/-40V.

What did also happen is that as the load was reduced in value, so the power went down in absolute terms, a sure-fire sign of the power supply being taxed over its capabilities and/or the output stages choking.

Ideally, I should have got 100/133/200W into 8/6/4 ohms, but what I actually got was 101/128/156W into 8/6/4 ohms. This was an older model, so it had only five channels, but all of them held up to this, give or take a watt or two. Since it was rated at 110W/6 ohms, I can only conclude that they fully and truthfully adhered to their own specs.

Only one stuck out, a NAD product. I forgot the actual numbers, but the point was that it surpassed its specs by quite a margin, one I wouldn't normally expect to find in HT gear at that price point.

This is not to say your logic is all wrong, simply to point out that, as ever, not all gear is created the same, not all manufacturers use skewed logic.

Regarding your comments on marketing, and in particular on percieved value, I can only agree completely. With sadness, I must add, because here we have a bona fide term taken from economic theory and distorted to no end. So very "in" these days.

Lastly, regarding your comments on woofer size, I think you should be a little more flexible.  As I'm sure you know, these days the panacea for bass delivery is to stick in two 6, 6.5 or at best, 7 inch woofers in parallel. While this does work if done properly, even a short form inspection of the quality of the drivers typically used in mass produced speakers will show two things, at least in very general terms: 1) those small drivers are usually dirt cheap, dinky little things you'd never dream of using anywhere else beside sound reinforcing your toilet, and 2) at 10" and above, most (but not all) even semi-serious driver manufacturers actually start working and producing semi-decent drivers at worst. I can only assume it's because the demand for 10" and larger drivers is so much below the demand for smaller units that it's becoming harder and harder to sell them if too poorly done.

Cheers,
DVV

[avahifi]

Excuses, excuses, excuses, pardon me.

125 watts into 4 ohms is a peak voltage swing of plus and minus 22.36068 volts!  Period.  No excuses.

That translates into 31.240563 watts RMS into 8 ohms.

If the manufacturer would have wanted to give an honest power rating, the unit would have been rated at RMS power into 8 ohms all channels driven for one hour, after one third power preconditioning for five minues.  And the sucker would still be working at the end of the hour.

Anything else is bullshit.

And if you think you are going to get that with all seven channels driven into an 8 ohm load continiously, think again.  What you are going to get is a fire, unless, of course, you have really high priced power cords and interconnect cables.  

Frank Van Alstine

[skrivis]

Not arguing with your math, Frank, but I don't think it works quite that way.

My lab experience with multi-channel receivers is hardly extensive, but I did have a few facing the works. And in all instances, they did deliver their rated power outputs in classic terms into 8 ohm loads in the usual FTC manner, you know, xx watts into 8 ohms, 20Hz-20kHz, at rated distortion or below. They delivered into 6 ohms as specified as well, probably because of the THX rating requirements. One was rated at 100W/8ohms, ...

Did you get these results when testing one channel, or all of them at the same time? Using the example box, they claim 125W X 7. It would not be hard at all to have a single channel at a time output 125W, but it's a different story if all 7 are being pushed at once.

This particular box has more problems than just the power amp. It looks like a microATX case, and they're pretty cramped inside. By the time you allow for the computer parts, there isn't much room for a 7 channel amp - especially if you want the whole thing to run cool. (Many HDs, CPUs, graphics chipsets, and motherboard chipsets put out a lot of heat and will die an early death if there isn't sufficient cooling.)

The inside of a computer is also not a very good place for audio circuitry. There's way too much RFI. The computer industry tends to ignore this. So what kind of sound card are they using? The total price seems to indicate that they're using mostly off-the-shelf parts, so are they using a generic sound card solution?

Is the amp circuitry properly shielded? That could be hard to do with the limited space, and even harder to properly cool.

I guess I'm pre-disposed to be skeptical. I've seen too many sound cards and too much car audio stuff that makes wild claims.

[BradJudy]

skrivis, the d2Audio modules are quite small:

Package with Integrated Heat Sink
• 6.8 x 4.7 x 2.5 in

[woodsyi]

This question may all be just academic!  I have a midfi bargain 7 channel amp for HT called Outlaw 770.  It claims to to generate 200W per channel driven simultaneously into 8 Ohms and 300W into 4 Ohms.  It also states maximum power draw at 1800W.  It think it's class AB.

I don't know if what they claim is true, but I know this.  I have never come even close to clipping this amp with my bookshelf surrounds and floorstanding LRs.   This includes any movies and 7stereo music listening.  I cranked it up to the point where walls were shaking (from volume matched self powered sub) and painful to the ears for about 30 seconds.  I turned it down because I couldn't stand it.  My room is 15'x22'x8'.  Who in an average size house needs 200 Watts 7 way into 8 Ohms continuously?

[BradJudy]

I'm guessing if you crack open a lot (perhaps most) of the amps out there, you will find a transformer that is not capable of handling the juice required to run all channels at the same time to their maximum rated capacity.

[DVV]

Excuses, excuses, excuses, pardon me.

125 watts into 4 ohms is a peak voltage swing of plus and minus 22.36068 volts!  Period.  No excuses.

Please look again at my post. I didn't say "125W/4 ohms", I said 156W/4 ohms. But this is purely a numeric matter.

That translates into 31.240563 watts RMS into 8 ohms.

If the manufacturer would have wanted to give an honest power rating, the unit would have been rated at RMS power into 8 ohms all channels driven for one hour, after one third power preconditioning for five minues.  And the sucker would still be working at the end of the hour.

Anything else is bullshit.
 ...

The manufacturer DID give an RMS rating into 8 ohms, quoting specifically "100 watts RMS into 8 ohms, all channels working simultaneously".

And that's what I got more or less. Before you ask - no, I did NOT have it running for an hour, I thought 5 minutes was enough. It could withstand 5 minutes of continous drive for 8 and 6 ohms, but even at 6 ohms, it got mighty hot. It's no easy thing to pack enough heat sinking into a single case for 5 channels, as we both know, and I had it running with its top removed. I'm not sure it would have withstood 5 minutes in a typical installation, with its top on, likely pushed inside a poorly ventilated cabinet or some such, but then, that's the problem of the user.

Into 4 ohms, it did deliver 5x156W give or take a watt, but it did so for only about a minute, when its overheat protection kicked in, muting it. I can't say I was surprised, but I was a little disappointed, to be sure. Then again, They simply had no space to fit in two 30 cm (12") side heat sinks rated at 0.2 K/w, as I would have done, and of course, the price would have been rather different.

Frank, we can split hairs about this for as long as you like, but all I wanted top do was to point out that not all manufacturers of multichannel receivers give meaningless specs, some actually do deliver on them. They have neither the space nor the price leeway to design for constant two ohm power delivery as I routinely do, and as I would imagine you do too, they can't walk my path and use 500 VA toroids for nominally 100W/8 ohm channels, etc. Such a receiver would be incredibly big, seriously heavy and very, very expensive.

But modest as they may be, some of their specs ARE fufilled to the letter, at least by some of them. In my case, Yamaha.

Cheers,
DVV

[avahifi]

My definition of the term "marketing" from about 25 years ago:

"Using fraud and deception to sell crud to fools."

I have not seen anything in recent years to cause me to modify the definition.

Frank Van Alstine

[DVV]

My definition of the term "marketing" from about 25 years ago:

"Using fraud and deception to sell crud to fools."

I have not seen anything in recent years to cause me to modify the definition.

Frank Van Alstine

Perhaps you haven't looked hard enough.

Overall, I agree with your assessment of marketing more than you think. It's a beast unleashed and nobody seems to even want to control it. I refer to those who are theoretically paid to create and enhance standards, as well as to enforce them. You have FTC in the US, over here in Europe, we have national agencies - all of which seem to practice being invisible.

Let me quote another, more recent example. A NAD receiver, I forget its model number, rated at 50WRMS into 8 ohms. It made a prompt mockery of itself by delivering 101W before onset of clipping, which is a generous +3dB headroom. Next, it kicked 102WRMS into 4 ohms, albeit for about 5 minutes before the overheating protection kicked in. In peaks, it will deliver 186 watts peak into 4 ohms.

Say what you will, but I find these results to be very cerditable for NAD. It has a sane power rating, which it fulfulls, and it is uncommonly load tolerant (for an HT receiver, that is). In fact, more so than many a dedicated integrated amp limited to two channels.

True, my own 50W per side amp will do far better, and will deliver 50/100/200 watts RMS into 8/4/2 ohms - but look at its size and price. And it's a two channel model only, has to be due to heatsink size.

Frank, I agree the worthy practices of the seventies are all but gone; if you remember, in those days you could bet your bottom dollar practically any unit you buy will surpass its specs, often by a very fair margin. I agree these days anything goes as long as you get the money, but there are still some honest peope out there, even among the (relatively) mass producers.

In fact, I think (hope?) I see a slow but sure trend of getting back to reasonable specifications. Look at NAD, Rotel, Denon, Marantz, etc, all of whom have not been caught out at nonsensical specs for a long, long time.

I hope we'll agree this bodes well for all of us, because sooner or later, the Mighty Copywriter will once again have to actually know what he's on about.

Cheers,
DVV