True Rms Power

[Workhorse]

I have gone through several amps namely INTER M , PSSAUDIO french amps etc.
Inter M korea amp manual claim 1000WRMS output @ 700VA max ac consumption , is it possible , Secondly PSS audio on their website claim that 1000WRMS amp can be powered by just 750VA rating transformer, then u can imagine from where the remaining 250 W are arranged.They simply states that they rely on large filter capacitors. Is it suffice.

WHEREAS, In our amps for 1000WRMS output the transformer is rated at 1800VA with max consumption is 2200VA @ 230VAC. With 60000MFD total filter capacitance.

PLZ give ur conclusions about these misconceptions.

[Tony]

from what i have learned in school, true power or simply power, is a product of rms voltages x rms currents, and the product of which is watt average...

i do not know how or why rms is still applied to power....

in manila, you will see local fabbed amps using 2n3055's running off 50 volt rails claiming a power rating of 1000watts, figure this one out!!!

[runebivrin]

Not exactly.

RMS voltage is the equivalent DC voltage, which applied to a resistive load would result in the same dissipated power as the original AC voltage.

RMS current is the same for a current through a resistive load.

Multiplying the two results in VA rating, but that in itself does not imply a resistive load. In fact, it is a value which is mainly used with reactive loads.

If you load a transformer with an ideal capacitor, there will be no power dissipated in the cap, but there's current flowing, so the transformer, which has a resistive element will still get hot. That's one of the reasons transformers are rated in VA, rather than watts.

As far as output power is concerned, it's simply a question of how long your measurment period is. For continous output, I would not recommend a transformer rated at less VA than twice the output power of the amp. Remember there's power dissipated both in the loudspeaker and the amp.

For home use, that's of questionable value, since very few run their amps with continous tones. Any music worth listening to has considerable variations in amplitude, and so should work quite well off of the caps and the fact that the transformer won't suffer from a few seconds of excess current, if it's allowed to "rest" inbetween.

For disco use with drum'n'bass or jungle or something rather more monotonous I would recommend 3-4 times the output power as transformer rating (or changing music )

Rune

[peranders]

Originally posted by amp_man_1
I have gone through several amps namely INTER M , PSSAUDIO french amps etc.
Inter M korea amp manual claim 1000WRMS output...

1000 watts for a while, not stated how long though....

[sreten]

It is common practice to use a transformer with a
VA rating ~ 70% of maximum rms output power.

On continuous sine wave testing it will overheat,
but on music program it will be fine as the peak
to average ratio of music program is 10 to 20 dB.

So driven hard into clipping on music program average
power of a 1kW amp is unlikely to exceed 250W.

sreten.

[lucpes]

Originally posted by sreten

On continuous sine wave testing it will overheat,
but on music program it will be fine as the peak
to average ratio of music program is 10 to 20 dB.
sreten.

Slightly off-topic here, but this issue disurves a good rant:

Not so true with nowadays 'pop' cd's, they are dynamically compressed, and the peak/average ratio is often 6dB or less! There's a loudness race in the (pop) music industry, where every year levels are pushed closer and closer to the maximum by the use of dynamic range compression. Which means that a Britney Spears CD from 2000 can be louder than a metal track from 1985. And an orchestra playing at full belt (over 100dB peak SPL!!!) is quieter than either, because classical music CDs haven't entered into this loudness race...

[sreten]

Not one to disagree with the hideous use of compression nowadays.

However 6dB range is the realm of lift music and bass channels
in (poor) live PA rigs, 10dB is a better estimate of "pop" music.

sreten.

[hunter audio]

hi

i just gave a dose on this subject in that desi thread t/s parameters i am copying and pasting from there as it deals on this directly -

what i have found out about these firang amps speacially PEAVEY

and then copying and pasting the entire thing i wrote other wise these firangs will start arguing - have to show them our level from the begining i guess !

-----------------------------------------------------------------------------------

this deals with ure subject

1) dealing with rms sine wave output

rms output is mostly specified in pro audio

my experience

peavey mentions rms output @ 1 khz (vocal range)

this has a lot of limitations as the max load on the amp and power supply is on when pushing bass

more often than not a peavey amp

rated at 1000 w rms @ 4 ohms bridged @ 1 khz
is actually somewhere around
500 to 600 w rms (bridged) @ 20 hz to 20 khz

this will be printed in their catalogue too but since its such a fine print quite a few over look it

there are pro audio amps like the crest audio pro series which do not fall in this category at all

summing up one should go for the rms - sine wave rating
@ 20 hz to 20 khz
and it may be deceptive when going by 1 khz ratings

--------------------------------------------------------------------

the entire thing (had to do with pmpo ets)
ref wattage
-------------------------------------------------------------------

what to look for prior purchase

the following are the fine print i have often noticed regarding wattage

firstly wattage

there are in a broad base 2 types

1 - rms output with a sine wave input

2 - rms output with a music power input

other than high end audio i have found more often than not - music power output is the common source of rating

music power output is not PMPO

music power is often 1.5 to 2 times the sine wave rms output of an amp (depending on the class of operation and output stage)

1) dealing with rms sine wave output

rms output is mostly specified in pro audio

my experience

peavey mentions rms output @ 1 khz (vocal range)

this has a lot of limitations as the max load on the amp and power supply is on when pushing bass

more often than not a peavey amp

rated at 1000 w rms @ 4 ohms bridged @ 1 khz
is actually somewhere around
500 to 600 w rms (bridged) @ 20 hz to 20 khz

this will be printed in their catalogue too but since its such a fine print quite a few over look it

there are pro audio amps like the crest audio pro series which do not fall in this category at all

summing up one should go for the rms - sine wave rating
@ 20 hz to 20 khz
and it may be deceptive when going by 1 khz ratings

2) music power rating

this has quite a few standards IEC 1 to 4

details are avalable in various sites

-what i have summed up along with personal experience is :

wattage rating has been very liberal when rating home theatre amps
even with amps supporting THX logo

what i have found is that mostly 1 transformer supplies 5 channels :- the current sharing is of concern

at any given moment where the main speaker woofer pulls high current

another channel may clip due to most of the current being taken up by the main speakers

clipping is of concern to all amp manufacturers as it will inturn destroy expensive speakers

to avoid clipping these amps have a high speed input to output comparator circuit and when clipping is detected the input is compressed automatically to avoid clipping

in turn limiting output to the speakers

there are ways of counteracting the above effent (by inguniesly placing reservoir caps along the speaker and power supply signal path and aid current sharing , which i have found most companys using) - yet the wattage rating always fall short when all channels are driven

they play loud but a better quality is achieved when pwoering the same set up with discrete amps

PMPO misleads people and is banned in most countries
i dont support it and am waiting the day when its banned in good ol India too !

suranjan

[sam9]

To complicate the matter, there appear to be more than one way to declare the maximum output:
1. Watts = [Vrails/(sqrt(2)]^2 / Rnominal

2. Replace Vrails with actual peak at clipping, usually 3-5 volts below the rail thus a lower figure.

3. Replace Vrails with voltage corresponding to the claimed THD+N figure resulting in a still lower rating.

The first is just arithmetic and even if factual isn't to descriptive of actual performance. No. 2 is a little better since it recognizes we are not in an perfectly efficient world. No. 3 comes is the one I prefer if only because it contrains the advertising copy writers at least a little.

[maylar]

Anybody else here old enough to remember IHF Music Power ratings?

The "power wars" of the late 60's and early 70's led to an industry standard method of testing that accounted for the dynamic nature of music, and the economics of using capacitors to suppliment power supplies for transients. The end result was power ratings much higher than pure RMS numbers, yet less than the absurd "IPP" (Instantaneous Peak Power) numbers being published by cheap Chinese audio companies.

I think most hifi buyers equate RMS to "continuous" power, and expect it to be the power you get when applying a sine wave. In that context, you can't get 1000 watts from a 750VA power supply. The only "cheat" I can think of is that you won't get full power to both channels of a stereo when both are driven together. One channel could be 500 wrms, but not both at the same time doing 1000 wrms. If it's a mono amp, they're lying.