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

[Ciaran]

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?

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.

 

[lovinthehd]

Is electricity that expensive there where this is an actual concern? You plan on operating it at full bore 24/7 or something? I'd be more worried about heat buildup in the room

 

[KEW]

I, personally would stay away because I live in a warm climate and the penalty of having to run more AC (both cost of electricity and increased background noise level) are bigger liabilities than any possibility that I might perceive any sound quality improvement. If I happened to live somewhere where the extra heat would be welcomed and electricity was inexpensive compared to other sources of heat (such as gas) I would give more consideration to Class A although I would still be concerned about reliability issues given the increased heat around my electronics.

 

[Verdinut]

First of all, the NAD 973 has differential Class A input circuits, but that does not imply that the power amps operate in Class A. They most likely operate in Class AB as with most currently produced AVR's. If they do operate in Class AB, then the AC power drawn when outputting a steady 1000 watts would be around 1500 watts, not much more.

However, in all practical situations, that would not happen. When playing a surround HT system, unless you were using the all channel stereo feature, most of the power used comes from the 3 front channels, and a lot less is demanded for all of the surround channels.

In my opinion, the cost of repairing is too high. I would suggest the Monoprice Monolith 7 channel power amp, which is very affordable, is built by ATI which is a reliable US company, and has excellent specifications. It's solidly built and the only negative aspect is its total weight of 93 lbs.

 

[Gmoney]

You guys remember Bob Carver’s TFM- Amp? the 25,35 and 45 and if I remember there was a 5 channel also. The reason I’m bringing this up is
I see those are still popular to rebuild or repair.
I been following a few of those on Ebay, what’s you guys Thoughts on those Carver amps. One dude had one going for 450 says it’s been to the repair shop caps replace meter replaced. It seems those are fairly easy to repair they been around for a long time. OP didn’t mean to derail your Thread.

 

[Ciaran]

Is electricity that expensive there where this is an actual concern? You plan on operating it at full bore 24/7 or something? I'd be more worried about heat buildup in the room

Haha - yeah its not really that much of a concern I suppose! And you don't get into home theater if you worry about the electricity bill. I guess I'm trying to find out if this amp is like a gas guzzler car from the 1980s, whereas the Rotel RMB-1555 I bought to replace it is like a Prius?! Or is there very little in reality between the two? A/B is more efficient, but not by as much as you would think?

 

[Ciaran]

I, personally would stay away because I live in a warm climate and the penalty of having to run more AC (both cost of electricity and increased background noise level) are bigger liabilities than any possibility that I might perceive any sound quality improvement. If I happened to live somewhere where the extra heat would be welcomed and electricity was inexpensive compared to other sources of heat (such as gas) I would give more consideration to Class A although I would still be concerned about reliability issues given the increased heat around my electronics.

Thanks - I live in Switzerland right now so we don't have home AC here, just a couple of fans in summer. Heat isn't a huge concern, but I do worry about heat build-up in my AV cabinet.

 

[Verdinut]

Haha - yeah its not really that much of a concern I suppose! And you don't get into home theater if you worry about the electricity bill. I guess I'm trying to find out if this amp is like a gas guzzler car from the 1980s, whereas the Rotel RMB-1555 I bought to replace it is like a Prius?! Or is there very little in reality between the two? A/B is more efficient, but not by as much as you would think?

The maximum efficiency for a Class A amplifier is around 40%, whereas that of one operating in Class AB can be over 70% in some designs, so it's not marginal.

 

[Ciaran]

First of all, the NAD 973 has differential Class A input circuits, but that does not imply that the power amps operate in Class A. They most likely operate in Class AB as with most currently produced AVR's. If they do operate in Class AB, then the AC power drawn when outputting a steady 1000 watts would be around 1500 watts, not much more.

However, in all practical situations, that would not happen. When playing a surround HT system, unless you were using the all channel stereo feature, most of the power used comes from the 3 front channels, and a lot less is demanded for all of the surround channels.

In my opinion, the cost of repairing is too high. I would suggest the Monoprice Monolith 7 channel power amp, which is very affordable, is built by ATI which is a reliable US company, and has excellent specifications. It's solidly built and the only negative aspect is its total weight of 93 lbs.

That's really interesting - I've never anything saying that differential Class A operates like Class A/B. Would you be able to point me towards an article that talks about this?

As regards replacing it with a Monolith, I wouldn't like to do that for a number of reasons. One, I've already replaced it once with a Rotel RMB-1555. Two, I live in Switzerland so the import charges alone would add 20% onto the shipped price. And three, I kind of like the idea of keeping well built stuff alive, and not scrapping everything. 850 Swiss francs is a lot, but wages are very high here for everyone, including for AV repairs.

 

[Ciaran]

The maximum efficiency of a Class A amplifier is around 40%, whereas that of a one operating in Class AB can be close to double that percentage, so it's not marginal.

Thanks - that gives me a lot to think about!

 

[lovinthehd]

Haha - yeah its not really that much of a concern I suppose! And you don't get into home theater if you worry about the electricity bill. I guess I'm trying to find out if this amp is like a gas guzzler car from the 1980s, whereas the Rotel RMB-1555 I bought to replace it is like a Prius?! Or is there very little in reality between the two? A/B is more efficient, but not by as much as you would think?

Now that Verdinut points it out it doesn't seem this is a class A amp in any case and rather AB so likely not much different in consumption from the majority of amps....if you want energy efficiency look at a class D design....

 

[Verdinut]

That's really interesting - I've never anything saying that differential Class A operates like Class A/B. Would you be able to point me towards an article that talks about this?

As regards replacing it with a Monolith, I wouldn't like to do that for a number of reasons. One, I've already replaced it once with a Rotel RMB-1555. Two, I live in Switzerland so the import charges alone would add 20% onto the shipped price. And three, I kind of like the idea of keeping well built stuff alive, and not scrapping everything. 850 Swiss francs is a lot, but wages are very high here for everyone, including for AV repairs.

The differential Class A circuit that I have been referring to is an input circuit as per NAD's specs. When we talk about a Class A or Class AB amplifier, it refers to its output stage not the input.

 

[Ciaran]

Now that Verdinut points it out it doesn't seem this is a class A amp in any case and rather AB so likely not much different in consumption from the majority of amps....if you want energy efficiency look at a class D design....

Well in that case maybe it might be time for me to try and resurrect it!

 

[Verdinut]

Now that Verdinut points it out it doesn't seem this is a class A amp in any case and rather AB so likely not much different in consumption from the majority of amps....if you want energy efficiency look at a class D design....

I refer you to Post #8 above.

 

[Ciaran]

The differential Class A circuit that I have been referring to is an input circuit as per NAD's specs. When we talk about a Class A or Class AB amplifier, it refers to its output stage not the input.

Ahh - that makes sense - thank you!

 

[lovinthehd]

I refer you to Post #8 above.

I don't disagree, but the majority of amps are class AB....for now.

 

[Verdinut]

I don't disagree, but the majority of amps are class AB....for now.

I agree with you on that , but the Class AB amp is quite more efficient than the Class A type as indicated in post #8.

 

[lovinthehd]

I agree with you on that , but the Class AB amp is quite more efficient than the Class A type as indicated in post #8.

Of course....and class A will never be the one there are a majority of....

 

[slipperybidness]

Is electricity that expensive there where this is an actual concern? You plan on operating it at full bore 24/7 or something? I'd be more worried about heat buildup in the room

Agreed, it is the heat from pure Class A that is a bigger concern to me, in Texas, over the summer!

The heat is not insignificant, when it is well over 100F outside and you try to maintain ~70F inside.

 

[TLS Guy]

Is electricity that expensive there where this is an actual concern? You plan on operating it at full bore 24/7 or something? I'd be more worried about heat buildup in the room

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.