True Power Meter like Accuphase - schematic wanted

[tiefbassuebertr]

Most power meters used in power amplifiers actually show the output voltage, although one's wattage is suggested (i. e. still the same displayed value independend of the connected load and independend of the signal frequency).

Accuphase claim, that their power indicator shows really the true instantaneous output power value.
This means at the same time, that I see clearly by the indicated values, if I have connected a low impedance speaker (e. g. 0,5 ohms ribbon loudspeaker).
Who knows about such indicator circuits ?

And what is very special by Accuphase to show always the true power level and not the voltage level?

And which other brands uses indicator principle like Accuphase?

[soekris]

Measure Voltage, measure current and then multiply to get Watt.

Voltage is easy to measure, current a little more complicated, Accuphase use a Hall effect based sensor, a new part to use will be the Allegro ACS714 (Digikey have them), isolated current measurement up to 30A, with a 1.2 mohm !! internal resistance....

Soren

[tiefbassuebertr]

Originally Posted by soekris

Measure Voltage, measure current and then multiply to get Watt.
Voltage is easy to measure, current a little more complicated, Accuphase use a Hall effect based sensor, a new part to use will be the Allegro ACS714 (Digikey have them), isolated current measurement up to 30A, with a 1.2 mohm !! internal resistance.... Soren

according your opinion it must be a very easy task to create such a power meter.
But about
Accuphase A-50V
I read:
Digital power meter shows true output levelsOutput power is indicated by a digital meter. The meter circuit senses the actual voltage and current levels delivered to the speaker. An analog multiplier circuit calculates the power for any given moment, which is then precisely displayed on the digital meter. Since the level of a musical signal normally fluctuates rapidly, power output would be difficult to read precisely with an analog meter. The digital circuit also takes the complex speaker impedance into consideration, providing an indication of true power at any time.
The hold time of the display can be switched between 1 second and infinite. When the power indication is not required, the meters can also be switched off.
basiclly the same informations on page 4 about
http://www.accuphase.com/cat/m-1000en.pdf (include power amp schema)
On both pics of this unit there is to find a custom made MCU for Accuphase.