A little bit of hype in the video title, but part of the build is occasionally stopping to run some tests to check conditions. In particular, I don't want this massive undertaking to go thermonuclear and set fire to my house in the process. All along I've been monitoring how hot it gets while doing different things and everything looks good, so far.
Why test with music instead of dummy loads? Because this will be playing music so it presents a more realistic scenario for the amps. And I've also tested into dummy loads, it just not as dramatic for video.
Of course this is with the amp sitting wide open and the temps will go up when the front and top cover go on, but I don't think it will go up enough to be a concern. It will go up even farther in a warm room stuck inside my equipment stand, but still should not enough to worry about. There will be more testing as I make more progress.

The amp started out cold (18 degrees C) when I switched it on in the morning. The heatsink temp went up to around 24 degrees after running for around two hours, then I turned on the music and let that play for over an hour. Only 4 of the 10 amps were driven, but the output power would be about equal to what it would be with 8 channels driven at high volume into my 4-way speakers.
For comparison, my older 6 channel amp runs at a slightly higher idle current (40ma / output with 4 outputs on each amp board) and has smaller heatsinks. It sits at around 50 degrees C at idle and has hit 70 degrees when driven hard. I built that amp 13 years ago and it's been in continuous operation ever since.

Another comparison is the Yamaha HTR I'm currently using in my listening room. That runs just slightly above ambient room temp and I've yet to notice any significant amount of heat coming from it. Based on that I know it is also running a fairly low bias current, yet it has amazingly low distortion and noise performance. It has 7 channels in a much smaller case with much smaller heatsinks.

By contrast, the Onkyo 2 channel receiver I have gets quite warm, but has a just barely audible amount of hiss when you put your ear to the tweeter. It is running at a much higher bias current and unless you go to extreme lengths to make a very smooth power supply, you give up some noise performance when you push up the idle current.

Some will swear that a higher bias sounds better (pure class A is regarded as the best sounding solid state amp topology), but I'm not aware of any blind testing that backs up that claim.
The A in class AB is the part of the output that's running in pure class A operation. That is, the transistors do not switch off. For best efficiency, you want just enough class A operation to prevent crossover distortion. Crossover distortion happens when the output transistors switch off completely. Some amps push that class A mode up (via higher idle current) to cover the first few watts of output, but the cost is lower efficiency and much higher temperatures.

For me, the proof is in the low distortion measurements. If it's faithfully reproducing the signal and has the power to do that with authority, that's all I need from an amp. I'd much rather have the amp running cooler and lasting longer as a result. Any audible difference would be so small that it couldn't possibly offset the lower efficiency and higher temps.

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