Why is my HK a space heater?

[crbaldwin]

Even in "idle" mode (powered on but not producing any sound) my HK AVR 235 puts out some serious heat. This seems like a significant waste of energy. Are the digital amps (e.g. Panasonic XR receivers) better in this regard?

[Jonomega]

yes, because digital amps are, on average, more efficient with power. Class A amps are the most inefficient and, as a result, a larger fraction of the total energy is converted to heat energy. This is why class A amps are generally very large and have very lage heatsinks to transfer the heat out of the amp and into the surroundings. A Class D amp may only take 350 Watts from the wall, of which your speakers see 320 of those watts. A class A amp may take 300 Watts from the wall, and only 200 of those get to your speakers. 100 Watts is converted to heat energy and lost to the surroundings. 100 Watts is similar to the amount of heat emitted by a standard modern-day computer processor at full load.

Many Class A/B amps, typical of what is available to the entry/mid level amplifiers run tepid. For example, my Rotel RB1070 never exceeds "warm" (40C) under any condition.

[crbaldwin]

Interesting. Thanks.

[whoaru99]

Actually, the class A amp is probably 300 from the wall, 200 into heat and 100 to the speakers.

But, the general idea is still on track.

Even within the typical class AB, some just seem to run hotter at idle than others.

Do you have the H/K well ventilated so the heat can dissipate freely?

[crbaldwin]

[QUOTE=whoaru99]Do you have the H/K well ventilated so the heat can dissipate freely?[/QUOTE]

It has ~6" of clearance over it in an enclosed cabinet with 3 decent ventilation holes in the back. This is the best I can do with a curious baby on the loose. I am just shocked by the amount of heat it generates. Everything in the cabinet is really toasty when I open the door...

[ggunnell]

Heat dissipation seems to be getting worse in AV equipment. There are reports here of both the Yamaha 4600 receiver and the Anthem D2 having heat related problems. Having owned the Yamaha 2500, 4600, and 2600, only the older 2500 ran 'warm' -- both the 4600 and 2600 were hot even at idle! And I was unprepared for the room heating effect of my Sony SXRD.

I'm still not sure switching power supplies are quite ready for prime time -- was it Ed Mullen who posted some scope photos a few months ago? -- but we're all going to need to make noise to manufacturers that we globally can't afford the direct and indirect (air conditioning) energy costs of these designs.

[cFoo]

This was one of the deciding factor for me. I ended up sending the HK back because the panny is able to do as good of a job for much cooler. I can't afford any more heat with the projector, MCE and xbox 360 (industrial strength heater) already in the room.

[whoaru99]

[QUOTE=crbaldwin]It has ~6" of clearance over it in an enclosed cabinet with 3 decent ventilation holes in the back. This is the best I can do with a curious baby on the loose. I am just shocked by the amount of heat it generates. Everything in the cabinet is really toasty when I open the door...[/QUOTE]

Perhaps you would consider adding a small fan to one of the vent holes to draw out some of the hot air.

[noah katz]

Actually, I believe class A always dissipates half of max power, so the efficiency is 50% at full output and goes down from there.

I have a 635, and I agree, it's a cooker.

[Jonomega]

[QUOTE=noah katz]Actually, I believe class A always dissipates half of max power, so the efficiency is 50% at full output and goes down from there.

I have a 635, and I agree, it's a cooker.[/QUOTE]

thanks for the added insight. As you probably knew, I was just making up numbers. I never thought as low as 50% efficiency though :eek:

[soundlovr]

[QUOTE=noah katz]Actually, I believe class A always dissipates half of max power, so the efficiency is 50% at full output and goes down from there.[/QUOTE]

A Class-A amplifier that's 50% efficient only happens in audiophile wet-dreams :p While 50% is the theoretical maximum efficiency of a Class-A amp, this is not acheived real-world. Think more along the lines of 15-20% The good side is that it's extremely linear and distortion is something for other people ;)

A good Class-AB amplifier will typically offer an efficiency around 40-45%

A Class-B amplifier is more efficient still and a Class-C amplifier is the most efficient of traditional-classed amplifier operations and is capable of reaching 90% (albeit with insane amounts of distortion).

Modern Class-D amplifiers can reach 96% efficiency (heading towards their theoretical limit of 100%).

I know Class-G and Class-H offer similar efficiency numbers to each other, but I can't think of anytime I've actually seen the numbers involved.

[tlf9999]

[QUOTE=soundlovr]The good side is that it's extremely linear and distortion is something for other people ;)[/QUOTE]


Class A doesn't offer, by itself, good linearity or low distortion. And coincidentally, most high-end Class A amps, because of their SE and low/no-feedback topologies, offer poor linearity and high distortion.

[QUOTE=soundlovr]a Class-C amplifier is the most efficient of traditional-classed amplifier operations and is capable of reaching 90% (albeit with insane amounts of distortion). [/QUOTE]

you would win the Nobel prize if you could find a Class C amp that is over 80% efficient, :).

it is also hard to find a Class C amp for audio applications - they are more common in radio applications.

[soundlovr]

[QUOTE=tlf9999]Class A doesn't offer, by itself, good linearity or low distortion.[/QUOTE]

Ummmm... yes, it absolutely does. Everything about Class-A is by far the most linear of amp designs and causes the least distortion (aka: the highest fidelity). That's the whole reason people want them! By definition, an amp is perfectly linear if the output is a faithful copy of the input (except larger and inverted). Class-A amps by design amplify across the entire input cycle such that the output signal is an exact scaled-up replica of the input without clipping (that's the defintion of Class-A). You'll note the definition of linearity and the definition of Class-A are in practice the exact same thing. Class-A = most linear and least distortion. That's not even a debate.

[QUOTE=tlf9999]you would win the Nobel prize if you could find a Class C amp that is over 80% efficient, :)... it is also hard to find a Class C amp for audio applications - they are more common in radio applications.[/QUOTE]

The discussion was about amp classes and efficiency. I never said you can find a Class-C home audio device and I'm well aware they're mostly only used in radio transmitters (where high efficiency is highly important). Any audio bullhorn uses a Class-C design and reaches 90% efficiency easily; sadly, nobody gave the inventor a Nobel Prize to my knowledge. Perhaps you should alert the Nobel committee that you've declared him eligible since you're apparently qualified to make that determination. :rolleyes: :p

[tlf9999]

[QUOTE=soundlovr]That's not even a debate. [/QUOTE]

if you don't know what you are debating, how can you debate?

linearity is device and topology driven. a typical SE Class A amp, for example, uses no feedback and the linearity depends on entirely on the device which usually isn't that great.

[QUOTE=soundlovr]Any audio bullhorn uses a Class-C design and reaches 90% efficiency easily;[/QUOTE]

only in your dreams.

To help you understand amp classes, why don't you list out their definitions (to you) as you seem to be deeply confused and let's go fromt here.

[tlf9999]

[QUOTE=soundlovr]I'm well aware they're mostly only used in radio transmitters (where high efficiency is highly important).[/QUOTE]

they use Class C there because fidelity isn't important (mostly FM or digital transmissions. AM transmissions are slightly different).

[SiriuslyCold]

[quote=soundlovr]By definition, an amp is perfectly linear if the output is a faithful copy of the input[/quote]

sounds like a Panasonic XR series ;)

[Luis Gabriel Gerena]

[QUOTE=SiriuslyCold]sounds like a Panasonic XR series ;)[/QUOTE]
I was wondering how long ...

[ClarkeBar]

Soundlovr...meet Professor tlf.

Class attendance is not mandatory...nor recommended. ;)

[soundlovr]

[QUOTE=ClarkeBar]Soundlovr...meet Professor tlf.

Class attendance is not mandatory...nor recommended. ;)[/QUOTE]

lol, nor of interest... nor worth paying for....

lets skip out and go for pizza :D

[ehlarson]

[QUOTE=soundlovr]A Class-A amplifier that's 50% efficient only happens in audiophile wet-dreams :p While 50% is the theoretical maximum efficiency of a Class-A amp, this is not acheived real-world. Think more along the lines of 15-20% .[/QUOTE]


Real world Class A operation is more like 1% efficiency. Most Class A designs are pushing out 100 watts or more of heat even in idle mode. Considering that most of the time your amp is delivering in the range of a watt or so to your speakers you are really throwing away 99% of the power the amp consumes.

I don't know what Class D theory says, but a lot of the Class D amps I've been looking at are running 10 watts or so idle. That puts you at about 10% efficiency in real-world use. A big improvement for sure.

[soundlovr]

[QUOTE=ehlarson]Real world Class A operation is more like 1% efficiency. Most Class A designs are pushing out 100 watts or more of heat even in idle mode. Considering that most of the time your amp is delivering in the range of a watt or so to your speakers you are really throwing away 99% of the power the amp consumes.[/QUOTE]
*twitch twitch*

You don't measure efficiency without an input/output signal! Most commonly, you measure efficiency at maximum output power. Using your approach, I could turn the amp off and claim 100% efficiency. Viva la power revolution!

[tlf9999]

[QUOTE=soundlovr]Viva la power revolution![/QUOTE]

you may want to make sure you understand a subject matter before you speak, like amp classes, linearity, distortion and efficency.

or you can stay out of the school with other drop outs.

[tlf9999]

Ummmm... yes, it absolutely does. Everything about Class-A is by far the most linear of amp designs and causes the least distortion (aka: the highest fidelity). That's the whole reason people want them! By definition, an amp is perfectly linear if the output is a faithful copy of the input (except larger and inverted). Class-A amps by design amplify across the entire input cycle such that the output signal is an exact scaled-up replica of the input without clipping (that's the defintion of Class-A). You'll note the definition of linearity and the definition of Class-A are in practice the exact same thing. Class-A = most linear and least distortion. That's not even a debate.

BTW, the theoretical limit of a class A amp isn't 50%