amp total power

How do they rate the power from an amp? To mean it seems misleading?

in what respect?  they usually give an RMS value is is fairly honest, and then the maximum power at 90% THD which is useless...

i saw a (well known brand) amp come through here the other day that boasted 1000 watts on the heat sink, yet was fused with a 30 amp fuse, so i looked up the specs in the service manual...it was 300 watts RMS.... maybe i'm just old ( i am ) but i remember when amplifier companies gave you honest ratings based on a reasonable THD level, like less than 1%.....

Well, actually it IS INTENDED to be misleading, especially in lower-end and mass-market consumer products.  As soon as marketing people figured out that people will buy audio products based on the listed power output, much of the truth in ratings went out the window.  Especially in car audio (but also in home gear and in computer audio) there is a false perception that "more watts = better."  So many manufacturers 'inflate' their ratings.  It is sad.

Not that I think manufacturers lie; undoubtedly the gear will do what they say.  But not necessarily in ways that are listenable.  I have tested car amps listed as "1000 watts" that do, indeed, produce peak output of 1000 watts.  But this is achieved at 20% THD and with severe 50% clipping.  This amp's max output before clipping was a whopping 64 watts!  So did the manufacturer lie?  No, the amp could produce 1000 watts without blowing the internal fuses.  Was the rating misleading?  Yes, very.

Look for ratings at 12 Volts, and less than 1% (0.1% is better) THD into 4 ohms (or higher) and they MIGHT be accurate and reflect what you can expect to get out of the amp.  Ignore "peak" or "music power" ratings.

In general, "Dynamic" is a code word for "peak."  AKA "Peak Music Power" or "Dynamic Headroom."  All made-up words for peak instantaneous (<10ms) output..

RMS refers to voltage and current, by the way.  Power is power.  The so-called RMS ratings are the number of watts the amplifier can sustain based on maximum RMS voltage and current capability.  But it is the best indication of true amplifier output... assuming the distortion rating is also suitably low.  I know of at least one poor-quality manufacturer (think fake German-sounding name) who rate their amps as "RMS Watts" but do not list distortion numbers.  When the amp was tested, it produced the rated power but at 15% distortion!  Recipe for burned voice coils....

Back when I first started in car audio as a hobby (in the early 90's), I was very turned off about MTX's amps. The sales guy at HH Gregg had told me at the time about their "dynamic" power rating/headroom and how they were so much better than the competition because of this fact. I immediately said "I think I'll look a round a little more, thanks" and haven't really given MTX a very serious thought since. Not saying that MTX isn't any good, it's just if that's what they were training their sales people to say, then they can count on me NOT being their customer.

I have to laugh at all the claims that I see in regards to wattage whenever I get the urge to look for something new. "760 total watts x 4!" when really it is more like 30 watts x 4 @ 4 ohms.

I am a true MTX fan, they do give you the true RMS ratings at 12.5 volts before they give you the dynamic power ratings at 14.4volts. A buddy of mine runs a Licenesed MTX repair facility and has tested many MTX amps over the years, even the very early models. They have all performed as stated by MTX. MTX is one of the reputable companies out there as far as ratings are concerned.

  I myself am looking to purchase an MTX 1501D mono amp to power my MTX 8104's. It is rated at 1000 watts RMS at 2omhs 12.5v and 1500 peak at 14.4. The amp will actually put out almost  1700 at 14.4v as tested by my friend and some of MTX's birth sheets will show this as well. MTX all the way.