How expensive is it to run a Class-A amp?

lovinthehd

lovinthehd

Seriously, I have no life.
If it is a true class A amp. It will use the same amount of power whether it is idling or being driven at full power. So they make a lot of heat and use lots of electricity. They use their rated power continuously. That also makes them very unreliable, unless they are very low powered like 10 watts per channel. The output devices never catch a break.

If you want a class A amp, then as I keep telling you the answer is Quad current dumpers which are true class A amps, but by sleight of hand. They run co0l and are very efficient and reliable.

A true class A amp in standard configuration is something to run a mile from.
It's the OP who is worried but it apparently isn't class A either......I don't want one.
 
P

PENG

Audioholic Slumlord
I bought a used NAD T-973 7 channel power amp a few months back. It worked for a few weeks then started humming loudly. A repair estimate to replace all the capacitors was 850 Swiss francs (approx 900USD).

My question is, if I pay to repair this amp, do class-A amplifiers bleed you dry on electricity bills (especially since the NAD advertises that it can output a kilowatt)? How inefficient are they really?
That is a class AB amp. It has several 3 build in fans and is quite heavy for a 140 W power amp so it is likely biased quite high, but definitely not class A.

I'm interested mainly because I just bought some R500s (moving my Q700 to the rear and my Q350s into storage), and from what I've read the R500s really benefit from power.
That's a general statement that people tend to say about a lot of speakers but reality is that KEF recommended 25-150 W. It has impedance dips to 3.2 ohm but impedance is benign.

Based on the impedance vs freq graph, I would consider it 4-6 ohm nominal, so any upper mid range AVRs rated 125-140 W will be fine and the NAD T973 would therefore be good enough. More power doesn't hurt but if not actually used then there is no audible benefits.


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M

mtrot

Full Audioholic
I live in Texas and use a mammoth Krell class A power amp for my front L/R channels. It's a decent sized house and I have a swimming pool in the back. So, between the 5 ton AC system, the pool pump, the pump for the Polaris, and all the lights, I don't think the Krell is adding to my electric bill to any significant effect.

Now, the amp does emanate a considerable amount of heat, which will raise the temp of the family room a degree or two when it is operating. Sounds pretty good though!:cool: Here is the Owner's Reference web page for the FPB 400cx if anybody can figure out what it would cost to operate it for about 4 hours/day:

file:///C:/Users/mtrot/AppData/Local/Temp/0162_020_MAN.pdf
 
Verdinut

Verdinut

Audioholic Samurai
I live in Texas and use a mammoth Krell class A power amp for my front L/R channels. It's a decent sized house and I have a swimming pool in the back. So, between the 5 ton AC system, the pool pump, the pump for the Polaris, and all the lights, I don't think the Krell is adding to my electric bill to any significant effect.

Now, the amp does emanate a considerable amount of heat, which will raise the temp of the family room a degree or two when it is operating. Sounds pretty good though!:cool: Here is the Owner's Reference web page for the FPB 400cx if anybody can figure out what it would cost to operate it for about 4 hours/day:

file:///C:/Users/mtrot/AppData/Local/Temp/0162_020_MAN.pdf
Well, that's a file on your computer which we can't have access to.

Also, the answer to your question depends on several factors:

The sensitivity of the speakers you are driving with the FPB400cx?

The dimension of your listening room and your listening distance from your speakers

The average to maximum SPL at which you like to listen to your music

The cost of a kilowatt-hour of AC power in your area
 
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lovinthehd

lovinthehd

Seriously, I have no life.
I live in Texas and use a mammoth Krell class A power amp for my front L/R channels. It's a decent sized house and I have a swimming pool in the back. So, between the 5 ton AC system, the pool pump, the pump for the Polaris, and all the lights, I don't think the Krell is adding to my electric bill to any significant effect.

Now, the amp does emanate a considerable amount of heat, which will raise the temp of the family room a degree or two when it is operating. Sounds pretty good though!:cool: Here is the Owner's Reference web page for the FPB 400cx if anybody can figure out what it would cost to operate it for about 4 hours/day:

file:///C:/Users/mtrot/AppData/Local/Temp/0162_020_MAN.pdf
Yeah you might try attaching the file to the post if its not too large for AH....
 
M

mtrot

Full Audioholic
Yeah you might try attaching the file to the post if its not too large for AH....
Ah, I see. I originally got it from a web page, didn't realize it was now a file on my computer. I tried to attach it with no luck. See if this link will bring it up. You have to scroll down to the bottom where the specs for the 400cx are.
www.krellonline.com/pdf/FPB_man_S.pdf
 
M

mtrot

Full Audioholic
Well, that's a file on your computer which we can't have access to.

Also, the answer to your question depends on several factors:

The sensitivity of the speakers you are driving with the FPB400cx?

The dimension of your listening room and your listening distance from your speakers

The average to maximum SPL at which you like to listen to your music

The cost of a kilowatt-hour of AC power in your area
The Signature IIs are rated at 93dB sensitivity.
I don't really listen all that loud, not sure the exact SPL.
I sit 10 feet from the speakers.
I was able to get this electricity plan at 7.5 cents per kw-h.
 
Verdinut

Verdinut

Audioholic Samurai
The Signature IIs are rated at 93dB sensitivity.
I don't really listen all that loud, not sure the exact SPL.
I sit 10 feet from the speakers.
I was able to get this electricity plan at 7.5 cents per kw-h.
If the speaker manufacturer's published sensivity is accurate, using the following link, you could get about 90 dB at your listening position, which is loud, with only 2 watts output from each channel:


For a 90 db SPL (Sound Pressure Level), 2 continuous watts from each channel would consume a maximum of 375 watts X 4 hours on a daily basis. That means 1.5 kw-h @ 7.5 cents = roughly 10-11 cents/day. Most of the 375 watts consumed would be converted to heat.
 
M

mtrot

Full Audioholic
Using the following link, you could get about 90 dB at your listening position, which is loud, with only 2 watts output from each channel:


For a 90 db SPL (Sound Pressure Level), 2 continuous watts from each channel would consume a maximum of 375 watts X 4 hours on a daily basis. That means 1.5 kw-h @ 7.5 cents = roughly 10-11 cents/day. Most of the 375 watts consumed would be converted to heat.
Thanks, that's about what I thought. And 4 hours per day is probably too high an estimate for my usage. So, it seems that even with a honkin' class A amp, it would not really run your bill up that much unless you listen all day long and have inefficient speakers.
 
lovinthehd

lovinthehd

Seriously, I have no life.
Thanks, that's about what I thought. And 4 hours per day is probably too high an estimate for my usage. So, it seems that even with a honkin' class A amp, it would not really run your bill up that much unless you listen all day long and have inefficient speakers.
Altho in the winter you could use part of the energy "bill" towards heating the room :)
 
lovinthehd

lovinthehd

Seriously, I have no life.
Back to the power consumption thing. If it runs full bore all the time how can it have standby consumption of 37.5W, "idle" of 175W and "max" of 3000W (assuming you have that out of your wall to begin with).
 
Verdinut

Verdinut

Audioholic Samurai
Back to the power consumption thing. If it runs full bore all the time how can it have standby consumption of 37.5W, "idle" of 175W and "max" of 3000W (assuming you have that out of your wall to begin with).
According to Krell's published specs, it consumes 75 watts in standby and 350 watts at idle. But if he doesn't drive it loud, it won't consume 3000 watts.
 
M

mtrot

Full Audioholic
Back to the power consumption thing. If it runs full bore all the time how can it have standby consumption of 37.5W, "idle" of 175W and "max" of 3000W (assuming you have that out of your wall to begin with).
I'm not educated or versed on amplifier design, but I found this in the user's guide about the design:

Krell Current Mode A proprietary Krell circuit topology in which the audio gain stages of a component operate in the current rather than voltage domain. This unique technology provides the component with exceptional speed and a wide bandwidth.
Krell Sustained Plateau Bias III A patented microprocessor control system that maintains Class A bias operation regardless of musical demand. Class A bias is the most accurate method used to amplify musical signals. The new Sustained Plateau Bias III software is featured in the Full Power Balanced X Series amplifiers and was developed from the algorithm utilized in the Master Reference Amplifier. Sustained Plateau Bias III maximizes an amplifier’s efficiency both in power consumption and heat generation.

Not sure what all this means.
 
lovinthehd

lovinthehd

Seriously, I have no life.
According to Krell's published specs, it consumes 75 watts in standby and 350 watts at idle. But if he doesn't drive it loud, it won't consume 3000 watts.
I skipped down too far when I was copying spec (450 instead of 400 model).
 
Verdinut

Verdinut

Audioholic Samurai
Class A bias is the most accurate method used to amplify musical signals. The new Sustained Plateau Bias III software is featured in the Full Power Balanced X Series amplifiers and was developed from the algorithm utilized in the Master Reference Amplifier. Sustained Plateau Bias III maximizes an amplifier’s efficiency both in power consumption and heat generation.

Not sure what all this means.
Well, Class A is not the only amplifier output topology which can accurately amplify music signals. Well designed Class AB and Class D amplifiers do provide as neutral and pure sound to the human ear as any Class A. As a matter of fact, most high fidelity amplifiers manufactured today operate in either Class AB or Class D.

With reference to their Sustained Plateau Bias, it's inexact to say that their Class A amplifier is efficient. It's a very inefficient amplifier as compared to either Class AB or Class D amplifiers. But has a heat generator, its efficiency is not to be questioned.
 
C

Ciaran

Enthusiast
Not to derail my own thread, but would anyone of you have an opinion over which amp I would then use to power my 5 main channels? The Nad or my Rotel RMB 1555 (with everything going through a
Denon X4300h). My main speakers are:

L/R Kef R500
C Kef Q600c
SR/SL. Kef Q700

Whatever amp not used for the main speakers would then power my height speakers:
Atmos (4X) Klipsch RP-140SA
 
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lovinthehd

lovinthehd

Seriously, I have no life.
Not to derail my own thread, but would anyone of you have an opinion over which amp I would then use to power my 5 main channels? The Nad or my Rotel RMB 1555 (with everything going through a
Denon X4300h). My main speakers are:

L/R Kef R500
C Kef Q600c
SR/SL. Kef Q700

Whatever amp not used for the main speakers would then power my height speakers:
Atmos (4X) Klipsch RP-140SA
I'd use the slightly more powerful NAD on the mains.
 
P

PENG

Audioholic Slumlord
Back to the power consumption thing. If it runs full bore all the time how can it have standby consumption of 37.5W, "idle" of 175W and "max" of 3000W (assuming you have that out of your wall to begin with).
That's because, as it claimed, the bias level was concluded by a microprocessor in such a way that it would vary with the music signal. Even at very high input level, the amp would only consumed 3000 W as needed, that is, not continuous. A dedicated 20 A 120 V line should be able to meet such demand for a few seconds without tripping the breaker.
 
lovinthehd

lovinthehd

Seriously, I have no life.
That's because, as it claimed, the bias level was concluded by a microprocessor in such a way that it would vary with the music signal. Even at very high input level, the amp would only consumed 3000 W as needed, that is, not continuous. A dedicated 20 A 120 V line should be able to meet such demand for a few seconds without tripping the breaker.
So this is unusual for a class A design?
 

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