I emailed Dennis Murphy, who's name appears in this document. Here is his reply:



Just thought some of you might be interested. I believe a standard for rating multi-channel amps would work something like running the front 2 or 3 channels at full power, and the remaining channels at 1/8th or 1/3rd power. This presents more of a real world scenario than a "continuous, all channels driven" spec.

Jason

Sorry Charlie. I think you misunderstood. My statement was that the rule, as is now clear, is probably a little more complex and outdated. My point, was that it is very unlikely that numerous companies would use this terminology and not get called on it if it really was illegal. Now deceptive .... thats a 'hole 'nuther kettle of fish. (another tuna reference).

[This message has been edited by morphsci (edited March 25, 2002).]

I'm curious if Jason made it clear to Mr. Murphy that the 770 spec clearly states 'all channels driven'. As for the rest - yes, the FTC discussion was pretty clear that they were still getting up to speed on the new multi-channel stuff.

The doc I cited seems pretty clear that 'associated channels' would be any that are driven within the same frequency range, but I'm sure the FTC is probably still pondering.


Charlie

It's hard to explain without pictures, but they are different shapes. If you go here:

http://www.hubbell-wiring.com/new/hub9811.pdf

You can see on page 2 a 15 amp receptacle on the left, a 20 amp on the right. The 20 amp is designed to accept either a 15 or 20 amp plug.

I could be wrong, but I suspect a device with a 15 amp plug shouldn't draw more than 15 amps over the long haul, discounting surges and so forth.


Charlie

How else would you calculate RMS power. It's simple Ohm's law.
Learn to design your own amps. You can start here;
http://www.diyaudio.com/

I suppose it depends on what you mean by 'peak'.

Take music out of it for a moment and lets talk power distribution. In a DC circuit watts is simply voltage multiplied by amperage. It gets more complex in AC due to phase angles and so forth which can make VA not equal watts, but in a resistive circuit (like a test load) RMS is computed the same as DC IIRC. So RMS volts times RMS amps would result in RMS watts, or AC watts that heat the same as DC watts would, not the AC watts as measured instantaniously at the peak of the AC waveform.

If you are talking about 'peak' as in musical peak then that's a whole different thing and isn't really germane to my point.

In any case the line input and speaker output are BOTH AC and both obey the same laws. You can't put in 1800 watts and get out 2100, that is the crux of the issue.


Charlie

Peak means peak. Any EE would know what peak means. RMS only applies to sinusoidal waveforms. RMS Voltage is computed by Vpeak
times square root of 2, RMS current is calculated by Amps(I peak) times the square root of 2. The rest is simple Ohm's law. Check your EE textbooks.
No one can use program material to spec a power amp. Sinusoidal waveforms are always used therefor any reference to program
material is completely irrelevant in this discussion.
Peak power may very well be applicable since transformers are rated with Volt Amps. Also, my calculation seemed to match what Outlaw
indicated in their post. As a telecom engineer I've never speced parts for a commercial audio amp and don't know what standard practices are used in the process.
As a DIY audio designer I've always went for overkill since I'm not designing to a price point. In my 450 Watt sub amp I used peak power and a 80% derating, the transformer is a 550 VA unit. This is a bit small but I've never had a problem (you can't be that picky with surplus parts). What do you use in your designs Charlie, I'd really like to know.

I did notice that Pass Labs 125W 5 channel amp has a maximum power spec of 600 W. The Pass amp is much more expensive and
conservative design than an Outlaw amp (or any of the other cheap amps, Rotel, ATI, B&K ect) and appears to be rated in the same manner as far as power dissipation is concerned.

RC,

That's all really cool. In interests of keeping it simple, do you agree or disagree that any device that draws 1 watt max average over time cannot output 2 watts average over time?

This is, in a nutshell, my point. Anything beyond that is needless complication.

The 770 is spec'd to draw AT MOST 1800 watts, yet is also spec'd to put out 2100 watts in some cases.

This might be of interest:
http://www1.tpgi.com.au/users/tps-seti/baloney.html


Charlie

PS - RMS can apply to any waveform - sine is easier to compute and most commonly used. To compute RMS (1) square the waveform function (2) average over time (3) take the square root.

[This message has been edited by charlie (edited March 26, 2002).]

Here's an interesting thought experiment:

(1) Build a 2100 watt monoblock amp that draws 1800 watts.
(2) Drive it to max output with a 60hz sine wave. A voltage reduced version of the power line is ideal.
(3) Use a transformer to bring the output RMS voltage to 120 volts.
(4) Sell the excess 300 watts to the power company, repeat 1-4, plugging each new amp into the output of the last one.
(5) Retire, move to Tahiti.


Charlie

QUOTE]Originally posted by Charlie:
RC,

The 770 is spec'd to draw AT MOST 1800 watts, yet is also spec'd to put out 2100 watts in some cases.
PS - ROMS can apply to any waveform - sine is easier to compute and most commonly used. To compute ROMS (1) square the waveform function (2) average over time (3) take the square root.

[This message has been edited by Charlie (edited March 26, 2002).][/QUOTE]

Yes, that is the true definition of RMS. This proves you knew exactly what I meant by peak. But I like being corrected in this manner.
I can't disagree with the figures we have here but I don't think they apply directly. This is what bugs me;
Pass Labs designs and manufacture ultra high end amps. I just don't see any reason for them to fudge on the specs, they doesn't advertise so there is no point. Since the amp is rated at 125W per channel all channels driven and yet dissipates only 600 watts something isn't right, just as you point out about the model 770. I think, and I'm speculating, that the 600 watts refers to the power the amp itself dissipates and not the total power which would be at least 1200 watts for the Pass amp.
In any case the Outlaw amp looks like a very good product. The heat sinks are big and judging from the weight the transformers are plenty big enough. It's not going to have the head room of an amp like the Pass Labs unit, but the Outlaw costs much less.
What got me to post is when someone on that other forum wrote that they weren't going to buy the 950/770 if Outlaw didn't come clean and release proprietary information. I hope that individual passes on the 950 so someone else can move up on the list.

BTW my dog is a perpetual motion machine and I don't expect I'll make a cent from him.