How hot is too hot?

Yes I'd say it was pretty normal it is by design. He probably has an amp that is in Class A mode which is a very inefficient mode but supposed be the best sounding. Class A is about 25% effiency and the other 75% is dissapated into heat. So if Class A amp is pulling 100w 25w goes to making sound while 75w turns into heat. I'm sure your amp doesn't stay in Class A mode past say 10w and it would then switch to Class A/B mode which is more effiecent at 50% but doesn't supposedly sound as well it's not as fast as Class A. So when you listen a quiet volume your amp gets hot but then when you crank it your amp will cool down when it switches to A/B mode because alot less energy is being dissapated and is being turned into sound. Since you have Klipsch speakers like I do you might have to play real loud for it to switch since they take less power to drive and therefore will stay in Class A mode longer. My 49TXi is Class A probably only for a few watts and then switches but if I turn it on and leave it on and don't play anything then it gets real hot sometimes you can barely stand to touch it but that's normal that's how Class A works.


Some receivers are in A/B all the time and there is now Class A mode you can tell because the receiver won't get hot when you turn it on. I think a cheap Yamaha I used to have did this it never got hot.


Here is some info about Class A, B and A/B modes


Class A:


Type of amplifier (amplifier class) in which both the negative and positive polarity output devices conduct at all times so that a current is always flowing through them. The result is a very inefficient amplifier at around 20 percent efficiency (it only outputs 20% of the power it gets from its power supply). Class A amplifiers are thus very large, heavy and hot-running amplifiers. However, since their output devices are always on, they can provide instant power in a highly linear fashion.

Class A amplifiers feature the lowest distortion and greatest linearity of the various amplifier classes. The output device of the amplifier is the electronic component that puts out power in watts to drive the speakers. Its polarity refers to the signal being negative or positive. A positive polarity output device does not need to be on when a negative polarity signal is present (this is how Class B amplifiers operate), however, if it is turned off it takes time to start it again when it is called upon to output power. So, class A amplifiers that always have full current to the output devices are ready to deliver power with no lag time and little distortion.


Class B:


The exact opposite of a class A amplifier, the class B amplifier completely shuts off its output devices when not needed (the positive polarity output is off when the signal is negative and the negative polarity output is off when the signal is positive). Class B amplifiers are very efficient compared to class A amplifiers, but they suffer from distortion and a fairly non-linear output.

When the positive polarity output device is turned off during a negative polarity signal, it is not ready to begin operation again very quickly. Where a class A amplifier can produce output instantly since current is always flowing, the class B amplifier must get started up again.

Think of a car sitting at a stop light. If it keeps the engine running at full power and full RPMs (using the brake to hold the car back), the car can take off immediately but it is less efficient (like a class A amplifier). If it turns off its engine at the stop light, when the light turns green the car must be re-started and put into gear before it can take off (like a class B amplifier). Invariably, output devices cannot be turned on and off instantly so the class B amplifier results in low linearity and distortion. Class B amplifiers are not used in audio products but are used in devices such as handheld CB radios where power reserves are important.



Class A/B:


A combination amplifier design using the concept of continuous current in both the positive and negative polarity output devices found in class A designs coupled with class B’s turn-off of unused output devices with the result being an amplifier that only allows very minimal current flow through output devices when signals of the opposite polarity are being created.

The class AB amplifier maintains current flow at all times so that the output devices can begin operation nearly instantly without the lags that doom class B amplifiers. However, complete current is not allowed to flow at any one time thus avoiding much of a class A design’s inefficiency. Class AB designs are about 50 percent efficient (half of the power supply’s power is turned into output to drive speakers) compared to class A designs at 20 percent efficiency.

Think of three cars at a stop light. The class A car keeps the engine running at full power and full RPMs ready to take off at any time. The class B car shuts off the engine entirely and must re-start and get in gear before it can take off at the green light. The class AB car keeps the engine running at idle with the gear in drive using some power but not as much as the class A car and being much quicker off the line than the class B car. Class AB amplifiers are the most commonly used amplifier designs thanks to their attractive blend of reasonable efficiency and high-quality output (low distortion and high linearity close to but not equal to class A amplifiers).


BTW almost every amp except very very expensive ones -like one Krell makes- operates in Class A and A/B modes. If you want your amps to stay in Class A longer buy more effiecent speakers or buy amps that don't switch to A/B as soon like Parasounds Halo JC1 which can stay in Class A mode for 25W which is about all the power you'll need and you could probably cook your hamburgers on it too when it gets that hot just don't let the grease get in the amp.


Daniel Smith