2. amps-preamps
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Watts and power

Can somebody break it down in layman's terms for me? Why is it that sometimes an amp that has a high watt rating (like, say, a lot of class D amps do) don't seem to always have the balls that much lower rated A or AB amps do? I have heard some people say, "It's not the watts, it's the power supply." Are they talking about big honkin' toroidal transformers? I know opinions vary on a speaker like, say, Magnepans - Maggies love power, right? A lot of people caution against using class D amps to drive them and then will turn around and say that a receiver like the Outlaw RR2160 (rated at 110 watts into 8 ohms) drives Maggies really well! I'm not really asking about differences between Class D, A, or AB so much as I am asking about how can you tell the POWER an amp has from the specs? 
128x128redstarwraith
audiozenology
362 posts
 
1) I have never made any claims about the SQ of the amplifier.

2) Do you have proof it cannot deliver the required current into 2 ohms to achieve 1500W?

3) What does "residue of current starvation" mean?   Are you implying they are selling an 8000W amplifier for < $400 now?  


Please explain in some detail, as you keep avoiding this, why you believe it is impossible for a Class-D amplifier to work properly into 2 ohms.


If it existed it would be PA, junk and it wouldn’t be getting it’s 1500w from a well designed amp with great current ability that can double down from 325w @ 8ohm and 750w @ 4ohms.
No, the 1500w would be the result of residue from current starvation from an amp that was originally 6000w or 8000w at 8 or 4ohms, and it would sound like junk

wolf_garcia
6,711 posts
 
After all of the back and forth regarding the watts issue, I was wondering if there's a simple device like my Radio Shack multimeter that could be stuck on the speaker output (or speaker input) jacks to see exactly how many watts I'm using to drive my allegedly 99db sensitive speakers at the levels I generally use. I know Nelson Pass uses something (and he likely has many bits of testing gear) like this at times while listening as it was referred to in some interview...the interviewer noted how few watts were used relative to the levels...I wanna do that...can I?
georgehifi's avatar
georgehifi
10,312 posts
 
wolf_garcia
Wolf, if you have a sample and hold oscilloscope, you can measure peaks, we did it to the Alexia’s powered up playing orchestral at normal medium level with the Gryphon Antillion, and saw amp peaks after conversion of 80amps+
Cheers George
audiozenology
362 posts
 
P = I*I*R.  Alexia's lowest impedance is 2 ohms. That means 80*80*2 = 12,800 watts (minimum) during that peak.


V = I * R = 80 * 2 = 160 volts minimum (to achieve 80 amps).


The Antileon is 175 watts into 8 ohms suggesting a maximum rail voltage of something probably a few volts over 37.5V. Even if current and voltage were 180 degrees out of phase at the impedance peak, you only have 75 volts (not the 160 needed to drive 80 amps into 2 ohms).

You will excuse me if I consider your 80 amp measurement suspect. What were you using for a current probe?






atmasphere's avatar
atmasphere
11,846 posts
 
You will excuse me if I consider your 80 amp measurement suspect.
Yes, indeed it is!! Assuming a one ohm load instead of two, the maximum current would have only been 37.4 amps. A bit of a stretch to see 80!
It can be tricky to interpret oscilloscope readings off of a running loudspeaker due to the phase angles involved- the peaks may well not represent what one thinks!
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