Axiom Home Page Forums General Discussion Technical Questions Amps and Power, for Micah

Where?

*looks around*

back in my car audio days, i used phoenix gold amps, and Dynaudio mid's and highs, with Boston Acustic pro subs.. i was in the SQ crowd... and the phoenix gold amps had very true ratings.. but you paid for that......


with amps today, there are so many technologies that companies are using, analog, digital, and a combination of both...

the best way for someone to understand how an amp works is to learn how a class A amp works, when you understand how a class A amp works then you have a firm basic knowledge...

http://sound.westhost.com/class-a.htm

in the home theater area, one of the biggest things to look at is the rating of the power supply, and the filter capacitors..

one example i am using is one of the amps that i have.
a Krell kav 250a

50,000 microfarads= uF of filter capacitance, a power transformer of 2kVA= (kilovolt amperes) rating


now for a yamaha RX-Z7 7.1 channel receiver.


(large E-core and 2 x 18,000uF= microfarads 71V capacitors)

i could not find the rating for the transformer..... but the krell amp is a 2 channel amp, where the yamaha has a 7 channel amp... and from the pictures the transformer in the yamaha can not even compare to the krell..



one reason the capacitors are important, the capacitors oppose a change in voltage, while a transformer opposes a change in current, as well as being able to change the voltage either up or down. depending on how you wire the capacitors and transformer in a perfect world neither the voltage or current will change... you have to keep in mind this is the power supply section of the amp... the is before your music is introduced into the circuitry...



this is a Krell amp, you can see the the majority of the amp is the power transformer, and at the top of the picture you can just barley see the blue capacitors. This is an older amp, but the electrical principles are the same no matter how old the electronics are.

this is one of the reasons that the pre-pro route is ideal solution, if money is not a huge deal.

No, Micah; an amp rated at 1000 watts per channel has to output that full 1000 watts continuously for at least five minutes with the number of channels required(at least two)being simultaneously driven. That's the test required by FTC regulations for all amps sold in the U.S.(and effectively, Canada as well). The 1/8th power test, which I've mentioned here several times in the past few years, is a different UL(Underwriters Laboratory)test for fire safety, which the unit has to survive without overheating. 1/8th isn't just something picked at random, it's been found to be a rough average of the power that's used in playing a typical music CD. That is, sometimes less than 1% of full power is used during the playing, at other times 100% might have to used, but the average over the 60-80 minutes would be about 12% of the full power rating.

This 1/8th power number is also typically the number used(unless specific language such as "full power" is used)when the manufacturer quotes a power consumption figure and puts it on the back of the unit. This misleads those who think it's consumption(including the dummies on the first page of the AVS thread Fred linked)at full power into thinking that the manufacturer is lying, since the consumption number shown is less than the full power output claim, and obviously amps work at less than 100% efficiency. As I've described before, the idea is that at 1/8th power class AB amplifiers are about 20% efficient(class D is somewhat higher), so a "7X100 watt" unit running at 1/8th of full power would be putting out about 90 watts total and would require about 450 watts input to do that. So 450 watts power consumption gets put on the back of the unit and the uninformed laugh/scream because obviously 700 total watts can't be output with 450 watts input when efficiency is well under 100%.

Fred, I got so disgusted with the silly talk on the first page of the AVS thread that I stopped reading. However, if you say that someone from Peavey later brings in factual information, I'll read the rest. Fortunately I read very quickly; I took one of them speed reading courses and was able to read War and Peace in 50 minutes(it had to do with Russia).

One point that I can add at this time is that the term "RMS" power or watts shouldn't be used, because there is no such thing(despite frequent use, sometimes even by manufacturers). Voltage continuously varies from about +170 to -170(in North America)and a special type of average called root mean square is used(comes out 120 volts)to show the effective overall voltage. This is used when it meets something(like a speaker voice coil) that has a resistance and results in power being used. A watt itself is a fixed amount of power and doesn't vary, so no RMS or other average is needed to express it.

John. The gentleman from Peavey goes by the handle of sickneedshelp and represents himself as one of the senior engineering staff at Peavey.

I usually pick up on technical stuff pretty quickly, but continue to struggle with all things relating to electricity.

Start at the beginning Fred (molecular level) and it'll become clearer. Also, don't believe the bullshit and stick to theory and math.

John - you're my hero.

Michael, i don't think we need to introduce hole flow into this conversation.....

But, I've been anxiously waiting.

cat, im not going to go into any further depth than my original statement on hole flow... ill let google teach you guys about hole flow if you want... but im not touching that one, without any formal education on electrical principles there would be no reason to understand it.

Quantum mechanics? That put me to sleep a couple decades ago.. You just carry one with that one. You an EE? My background is in power generation and reactor operation. Wish I would have followed through with some college, but met a girl and got distracted……. Story of my life.

Man, I wish I had girls as an excuse for my limited usefulness.