Why do some amps run so hot? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 9 Old 06-25-2019, 02:25 PM - Thread Starter
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Why do some amps run so hot?

I recently went to BB to look around. I noticed that many of the receivers/amps in the Magnolia display were too hot to touch on top. They are on all day, and they generate lots of heat. Is there a reason why? Is it a bad thing? Isn't a cooler running receiver/amp a better thing?

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post #2 of 9 Old 06-25-2019, 02:28 PM
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yes it is a bad thing for the amp to run hot constantly. This is why many people buy something like the Aircom cooling fan to put on top.

https://www.acinfinity.com/receiver-...g-fans/#scroll

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post #3 of 9 Old 06-25-2019, 02:54 PM
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Quote:
Originally Posted by jeff_s1520 View Post
I recently went to BB to look around. I noticed that many of the receivers/amps in the Magnolia display were too hot to touch on top. They are on all day, and they generate lots of heat. Is there a reason why? Is it a bad thing? Isn't a cooler running receiver/amp a better thing?
They're in small cabinets w/very little airflow. I have my gear in open racks w/plenty of air from all sides. I also have two Class A amps that are on open amp stands. Heat is one of the big killers to electronics.
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post #4 of 9 Old 06-26-2019, 08:13 AM
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It could also be because of the receiver/speaker combination. Under-powered receiver and inefficient speakers = heat.
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post #5 of 9 Old 06-26-2019, 08:28 AM
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Quote:
Originally Posted by jeff_s1520 View Post
I recently went to BB to look around. I noticed that many of the receivers/amps in the Magnolia display were too hot to touch on top. They are on all day, and they generate lots of heat. Is there a reason why? Is it a bad thing? Isn't a cooler running receiver/amp a better thing?
It depends on airflow around the amp and amp's architecture. Class A amps produce more heat that Class AB amps and they produce more heat than Class D or Class T amps.
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post #6 of 9 Old 06-26-2019, 10:19 AM
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As a side note. This is another good reason Not to buy Demo Gear from Stores like this. Assume everything, Speakers, Amps, Receivers have all been pushed hard and run far too hot in small "poorly ventilated" enclosures. Visualize if you can the 12 year old who runs in the room and cranks the Volume to Max.
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post #7 of 9 Old 06-26-2019, 01:41 PM
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With linear amplifiers (classes A, A/B and B) you have a given rail voltage (usually 2 rails, + and -) and your output transistors modulate their impedance in such a way that the transistors create a voltage divider with your speakers. Your output transistors sink all the voltage that isn't going to your speakers. However they are not constant power because when the speakers receive less power, the transistors receive more voltage, but your total impedance is higher (because the way the transistors sink more voltage is to increase their impedance). This is why I personally advocate, when using linear amplifiers, to use those appropriately sized for speakers and room that you'll use them in. Because a higher power amp will have a higher rail voltage and if you're not actually using that power, then it's going to dissipate inside the amp and heat it up. The heat created in the amp is not itself linear however. You can lessen this effect and increase overall efficiency by using other class amplifiers like D, G or H. Class D utilizes PWM so the transistors basically create a specialized type of square wave that when run through a tuned filter it will result in an analog output signal. Classes G and H use multiple rail voltages and switch between them as your output power requirements vary. Those types of amps will still create heat, but can create less heat than the typical Class A/B amp.


In any case, more heat always means lower reliability in electronics, be it your computer or your amplifier. With computers it gets even more complex than amps (look up "electromigration"). But it still matters for amps.




Some receivers offer "eco mode" which you should use if you aren't using a lot of power. I had a Marantz SR7011 that was running hot when I was literally not using its built-in amps at all. Bad design there. Eco mode helped somewhat. I sold that receiver though. There was no acceptable reason for it to run hot when I didn't even use its amps. Onkyo runs hot too. You go to the store you probably see a bunch of cheap Onkyo junk on the shelf. Avoid that in my opinion.

Last edited by DonoMan; 06-26-2019 at 01:45 PM.
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post #8 of 9 Old 06-26-2019, 04:14 PM
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IMHO...
1 primary reason is that due to intense price competition, the brands especially @ the popular market price-points have decreased significantly their overdesign for heat sink area and power supply capacity..
1 good indicator is the greatly reduced warranty period of their latest products compared to several years back..

Just my $0.02...
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post #9 of 9 Old 06-26-2019, 04:20 PM
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Quote:
Originally Posted by Adamg (Ret-Navy) View Post
As a side note. This is another good reason Not to buy Demo Gear from Stores like this. Assume everything, Speakers, Amps, Receivers have all been pushed hard and run far too hot in small "poorly ventilated" enclosures. Visualize if you can the 12 year old who runs in the room and cranks the Volume to Max.
Hey, that was me! (Decades ago.) None of the stores I went into then are around anymore. Best Buy wasn't even a twinkle in Mr. Buy's eyes back then.
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