Originally Posted by alexbarbel
The thing that intrigues me is the big differences that people report. Some say the unit barely gets warm and others say it is almost too hot to touch.
Mine is somewhere between but hotter than I expected from my experience with various stereo amps.
It has never cut out and so I presume it is OK and I will be able to shut the central heating off in my cinema room next winter !
Without a schematic it's hard to get a really good idea of why these variations in heat output from the SR7010 may occur, but hey, why be confused by the facts?! Here are some ideas:
Sources of heat:
Video/initial audio process board: This board has to have fixed, closely controlled, low voltages to operate correctly. It like generates quite a bit of heat since many of its circuits operate at very high frequencies; that's why it's the top board in the unit, but that heat generation shouldn't vary greatly between units unless the board is redesigned.
HDAM Audio Board: The analog circuits on this board operate in Class A and thus generate significant heat. The circuits appear to be supplied by resister based current sources (based on a circuit diagram from the AV7702) and hopefully by regulated voltages supplies. All of these components generate significant heat, but it's hard to see how their operation would vary significantly between units, again unless redesigned. The AV8802 pre-pro has a balanced output and twice as much of this circuitry. The circuit boards that contain the circuitry are mounted vertically to aid in dissipating the heat, which should the circuitry does generate significant heat. Quality analog circuitry typically, but not always, generates a lot of heat.
Power Supply: The big transformer perhaps only supplies the output power amplifiers. It's an EI type which is less efficient than a toroidal type unit, but should be quite consistent in operation between samples of the same product. Likely several other power supplies are present, some switching types. It seems unlikely that they generate a lot of heat so even if their heat output varies that shouldn't greatly affect the total heat output of the overall unit.
Power Amplifier: This seems a likely spot for variation. The circuitry appears to be Class B, likely with a goal of optimum bias. Some call it AB. The bias for each amplifier channel is likely set by varying a variable resister at the factory based on a voltage reading at one or more test points. If the bias is set too low then the amplifier channel will suffer too much crossover distortion. If it is set too high, the channel will operate in Class A for more of the signal swing and generate a lot more heat. Likely this setting is to be done when the unit is at a typical idling temperature. If the unit is too warm or too cool, the operator is having an off day, or any number of other variables are not as specified then the unit may run hotter or cooler in normal use, because of the actual bias setting.
Other ideas are that the product as designed was found to run too hot so the size of the output resistors was increased. This likely would cause the bias current to be lower with less heat generated. A set of lower value resisters may have been used for some reason, perhaps the unit ran cooler than expected so bias was increased, which would raise the bias current. A higher bias current should allow more tolerance for good bias tracking with unit temperature changes without risking increased crossover distortion. There are lots of reasons for potential variation in the setting, such as known or unknown changes in components or their tolerances. It seems probable that the setting of the bias for all the channels would be likely to be consistent if unit temperature is the reason for the variation.
The above is frankly a lot of guess work. What are the thoughts of others on this subject?