What is a high current amp??

[Petrol]

:\ I wonder how in the heck I did that ^^^

[DrWho]

Ya, your Sony draws a maximum of 300W from the wall...so assuming 75% efficiency you're talking 45W max

per channel. Give yourself 10dB of headroom and you're talking 4.5W per

speaker which is probably around 105dB continuous - not very loud and

would correlate to your feeling it lacks the live feel.

Just to make an example, the Denon power supply draws a maximum of 850W

from the wall (7.1 Amps at 120V AC). Assume 75% efficiency and you're

talking 120W per channel. Ironically that's what they claim for the

front channels. [] You'll get a little more dynamic power out of the

system because of the capacitor banks in the power supply, which is

probably how they get their slightly larger ratings at higher

distortions. With the RF-7's you're talking closer to 110dB continuous

which is getting into concert level, and you'll have a lot more

headroom compared to the Sony reciever.

I suppose I could run the numbers for the yamaha and HK, but I gotta

get running to practice right now. You can usually find the power

consumption ratings on the reciever in the back of the manuals. For the

Sony it's on page 70 in this PDF:

http://www.docs.sony.com/release/filedownload.asp?Sub=&file=STRDE995.pdf

And the Denon is on page 105 in this PDF:

http://usa.denon.com/AVR3806DFU.pdf

If only the current is given, multiply it by 120 to get the power.

Hope this helps.

[Petrol]

you kidding? That helps alot! I had seen consumption ratings many before and never paid them any mind, lol

Thanks []

off to the websites, lol

[D-MAN]

The term comes from the old days when most tube amps were current-limited in that the plate current is restricted to tube limits, or it would smoke the tube or worse. Therefore a tube is a high voltage, low current device. The power rating (Ohm's law) is Power (in watts)=current x voltage, or P=ie.

Transistors are technically not current-limited, being low voltage, high current switching devices.

Even thought the output wattage may be exactly the same for both amp types, the ratio of current-to-voltage to arrive at the same exact power output is entirely different.

DM

[Zen Traveler]

anyway, with all this talk about amp ratings, does anyone have any links to some 'Bench-Tests' showing what these things 'really' deliver?

Here is a link to a Benchmark test for the Denon AVR 4806: http://www.hometheaterhifi.com/volume_12_4/denon-avr-4806-receiver-12-2005-part-5.html

[pauln]

"...around 105dB continuous - not very loud..."

You are either kidding, mistaken, or your ears are fading from abuse... 105dB continuous is extremely loud.

[Zen Traveler]

I included this link on page 3:: http://www.hometheaterhifi.com/volume_12_4/denon-avr-4806-receiver-12-2005-part-5.html

Are the Denons considered 'high current" AVRs? The power consumption on my AVR 4806 is 10.6 A. []

[Islander]

And then there are Class D amps. While most "ideal" Class A or AB amps double their wattage as impedance is halved (500W into 8 ohms, 1000W into 4 ohms, etc.), even high-end Class D amps don't. 500W into 8 ohms, 650W into 4 ohms is more typical. Could this be caused by an inadequate power supply, or is it just the nature of that amplifier type?

[unimorpheus]

Just to add more fuel to the fire, in the 70s there was a rating that started to show its head (I dont know if it is still in use) and it was called MUSIC POWER. You could have two amps rated at say 100 watts, one was RMS the other was MUSIC POWER. The RMS amp would produce approximately TWICE the current as the MUSIC POWER amp. The difference was that the first amps rating in watts was for RMS (Root Mean Square) watts and the second amp MUSIC POWER was PEAK TO PEAK watts. RMS means the AVERAGE voltage in the sine wave, which is for the sake of argument approximately ½ that of peak volts. MUSIC POWER or PEAK TO PEAK is the measurement of the tops of the peaks of voltage thus throwing OHMS law a curve and gives a false reading of watts available in the amp. This was a marketing ploy to sell lower power amps in the AMP WARS of the 70s. I wonder if this is still in effect today with different names such as NORMAL and HIGH CURRENT ratings.

For even more fire:

The important value for amp rating is RMS power at a said distortion level over a prescribed frequency band. i.e. 100Watts RMS @ 0.01% total harmonic distortion from 20Hz-20KHz @ 8ohms. This means the amp will deliver clean power into this 8ohm load with low distortion over the entire usable frequency band. The RMS value for a sine wave is 0.707v * Peak to Peak voltage or ruffly 70.7% of peak to peak. This is important as it represents the equivalent DC power of an AC signal or amplifier output. The problem with your RF-7s is their impedance dips to a lower value at some frequencies. At these frequencies and amplifier's power supply may become unstable at higher volume levels (i.e higher current draw). This is why most solid state amps use toroidal transformers and large capacitors in the power supply stages. The capacitors serve as current reservoirs that can dump high amounts of current on demand but only for a sort time. A "High Current" amp has the ability to meet the current demands of a speaker's fluctuating impedance. This current delivery capability is also referred to as "dynamic head room" or again the ability of an amp to deliver that extra power when needed. This does not imply the amp is performing some magic to provide greater power than it is designed to provide. Manufacturers of "High Current" amplifiers simply underrate their amps to leave room for the dynamic power requirement. These high current amps usually could be rated at higher watts RMS than they are advertised. Conversely using a 400Watt RMS amp for a 100Watt application will also provide dynamic head room as well. Just as a side note a typical US home outlet provides 15 or 20 amps max before a breaker trips. This becomes a limiting factor in amp design unless you use different branches of you breaker box to feed multiple amps.

[mas]

nevermind

[mas]

why bother

[Groomlakearea51]

For even more fire: ..... This current delivery capability is also referred to as "dynamic head room" or again the ability of an amp to deliver that extra power when needed. This does not imply the amp is performing some magic to provide greater power than it is designed to provide. Manufacturers of "High Current" amplifiers simply underrate their amps to leave room for the dynamic power requirement. These high current amps usually could be rated at higher watts RMS than they are advertised. Conversely using a 400Watt RMS amp for a 100Watt application will also provide dynamic head room as well. Just as a side note a typical US home outlet provides 15 or 20 amps max before a breaker trips. This becomes a limiting factor in amp design unless you use different branches of you breaker box to feed multiple amps.

Exactly!!! Contractors are here for the "dedicated" stereo/ home office/ man cave/ room and the electrican is pissed because I specified 2 separate 30 amp service breakers for the two wall outlets on the "equipment wall". Oh well, that's life and he'll just have to get over it..

But..... Even though I'll be running a pair of Klipschorns with an AU-11000 and a "center pair" or Cornwalls with another AU-11000, at low volumes (as in low nominal voltage draw), I'll always have the "headroom" necessary for peak transients. The AU-11000's are in the "conservative" bunch and only rated at 115 WPC, but..... they can do 350-400 peaks without even getting warm.... But interestingly, their max current draw at the wall is 550 watts. That's pretty high for an amp rated at only 115 wpc.... But, as pointed out in the other posts regarding how ss amps have the power to manage peaks, in the case of these amps, they have dual toroidial transformers (one for each channel) and a massive array of caps just to make sure they can do the peaks.

MAS: Comments on how these things work in the "wall of voodoo"?

[mas]

Marshall, they definitely worked and sounded great. And they run amazingly cool.

And using multiple amps to adjust gain levels of the various sources provided for extensive soundstage variations.

On the subject of ratings, one wonders if we will ever move beyond wattage to meaningful specs. Its sad when folks buy an amplifier and speakers and light bulbs using the same units, and for all intents and purposes, for the same purposes, despite neither rating providing a meaningful representation of the primary performance of either product.

But if you need a heater, you're in luck!!

[Arkytype]

unimorpheus, et al---

While we may measure the voltage and current being delivered to our loudspeakers in RMS volts and RMS amperes, the power delivered to the loudspeaker is not an RMS quantity. We want the equivalent DC heating power and the AC equivalent of that quantity is average power. In short, there is no such quantity as RMS power. You won't find it in any electricdal engineering textbooks. You might compute it (see link article), but the result will be meaningless.

As far as audio amplifier output ratings are concerned, the usual method is to feed a 1 kHz tone to the input and measure the unclipped output into a dummy load. The resultant power calculated from E*E/R is properly called "continuous average sinewave power" (CASP).

This measurement is usually done after a 1/3 power "conditioning" cycle some nitwit at the FTC came up with. As you may know, operating a Class A-B output stage at 1/3 power is a worst case condition for heat generation. As a result, in order for an amplifier to meet the 1974 FTC rules, it had to have fairly massive heat sinks which meant the consumer was once again screwed, blued and tattooed by the law of unintended consequences.

Unfortunately, you will find otherwise reputable amplifier manufacturers using the RMS power term to rate their products. Many years ago, McIntosh adopted the CASP rating in their product data sheets. As was mentioned in an earlier post in this thread, there were inflated power rating claims which led to the 1974 regulations.

Here's how some of the advertized peak or peak instantaneous power ratings came about. An amplifier manufacture could literally bypass the power supply in its amplifier and substitute a laboratory power supply with plenty of peak output current capacity. Then, short sine wave pulses were fed to the amp under test and (assuming the output devices didn't fry) the resulting peak power output would be several times the CASP that is common today.

The link has a pretty good explanation of "RMS power" if mine wasn't clear enough.

http://www.hifi-writer.com/he/misc/rmspower.htm

Lee

[Zen Traveler]

...On the subject of ratings, one wonders if we will ever move beyond wattage to meaningful specs. Its sad when folks buy an amplifier and speakers and light bulbs using the same units, and for all intents and purposes, for the same purposes, despite neither rating providing a meaningful representation of the primary performance of either product.

mas, Thanks for the reading material--I printed it out will see if I can wrap my brain around it. FWIW, I purchased speakers and wish it were more cut and dry on what the acceptable jargon is to find what drives them efficiently...As soon as I find out I am outta here;-)

[garyrc]

Lee (Arkytype), and everyone:

As far as audio amplifier output ratings are concerned, the usual method is to feed a 1 kHz tone to the input and measure the unclipped output into a dummy load. The resultant power calculated from E*E/R is properly called "continuous average sinewave power" (CASP).

I'm still a little confused. A good dealer measured my NAD "150 watts per channel" amp (C272) at 171 watts per channel just below the clipping level at 8 Ohms (37 volts ROMS), with both channels driven.

1) What would my CASP be?

2) What does ROMS mean?

3) At the time, I had figured that my RMS wattage (which I now know is imaginary) would be .707 x 171 or about 121 watts (rounding), and that NAD must have used some other formula to rate the amp at "150 watts" -- do you have any idea what formula/method they used?

In redoing my music / movie room, should I ask for 20 amp circuits and AC wall outlets? 30 amp circuits and plugs like Groomlakearea51 ? Where online does one buy a 30 amp wall outlet?

Thanks

`

[BS Button]

It's kinda sorta like comparing torque with horsepower, NO?

BS[*-)]

[BEC]

"The RMS value for a sine wave is 0.707v * Peak to Peak voltage or ruffly 70.7% of peak to peak"

 

One too many peaks in that formula.  RMS = 0.707 * peak

Bob Crites

 

[Zen Traveler]

I got this from info from the link to the Secrets Denon AVR 4806 Benchmark test. I tried to follow the technical explanations, but have to admit some of it is over my head...Does this info help give anyone a more informed opinion of the compatibility of this AVR with my HT listed in my signature;-)

Preamplifier

Maximum RMS Output Voltage at Pre-Out

6.34 volts RMS

10 Points

We prefer at least 1.0 volt RMS, and 2.0 volts RMS is best. The AVR-4806 has outstanding voltage output. The maximum pre-out voltage was obtained using 1 kHz analog input, 2.44 volts RMS output from the sound card, and a volume setting on the AVR-4806 panel of +11.0 dB.

Power Amplifiers

2 Channel Maximum RMS Power Output

182 watts x 2; 0.14% THD; 2.44 volts RMS input

10 Points

To get the full 10 points, the 2-channel maximum output must be at least 30% above the rated output for all channels driven. This would be at least 169 watts per channel for the AVR-4806. This capability is tested with a variable transformer that keeps the input voltage at 120 volts when the amplifier is delivering its maximum output.

7 Channel Maximum RMS Power Output

114 watts x 7; 0.06% THD; 2.44 volts RMS input

0 Points

Output with all channels driven must be at least 95% of rated output, when testing with a variable transformer that keeps input voltage at 120 volts. For the AVR-4806, this would be at least 123 watts per channel (the 4806 is rated at 130 watts RMS x 7).

[DrWho]

"...around 105dB continuous - not very loud..."

You are either kidding, mistaken, or your ears are fading from abuse... 105dB continuous is extremely loud.

105dB continuous in the sense that the amp can handle peaks at that level without any worries of distortion (aka, linear range of operation) - with a mediocre 30dB of dynamic range, you're talking a measured 75dB on a ratshack meter...maybe 80-85dB depending on how compressed the music is. That's still nowhere near live levels.