106F isn’t out of range. As I mentioned the thicker copper in the boards spreads it around and there are local hot spots (say the regulators) which run cooler in the Mk II since the unit as a whole has more even heat spread. The video opamps in the Mk II draw somewhere between two times and four times as much current as their cousins did in the DS. In a linear supply that causes a lot more heat upstream in the linear regulators as well. (In the TSS there will be another doubling of this current.)
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I received a new MKII on Friday. I am breaking it in now with using a USB drive from my PST with continuous music for the last few days. The MKII is only running at 88F to 90F across the top of the unit and in the front. The hottest point on the back is 103F.
Thanks. I’m guessing a 3 degree difference is probably within the range of room ambient variability. I’m down in FL and I don’t keep the house too cool this time of year.
Not that I think 106F is much of a concern, but all this talk makes me wonder if there are any good arguments against leaving my MKII on 24/7. @tedsmith, do you think there might be any long term considerations around operating at such temperatures, such as evaporation of electrolyte in capacitors, or do you think it would be years beyond any reasonable period of ownership for that to even register as a concern?
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Good question. I suspect Ted’s got a good answer. 
All of the electrolytic capacitors are rated at at least 5000 hours at 105C. Some 5000 at 125C.
To calculate the expected lifetime of an electrolytic cap you double the lifetime rating for every 10C drop from the rated temperature. The guts of the DAC are designed to stay below 50C (122F) at the worst and to be below 40C (104F) typically. At 50C the lifetime should be extended by 2^((105-50)/10) or about 45 times. 40C gives approx. 90 times. 5000 hours * 45 is approx. 25.8 years. 5000 * 90 is approx. 51.6 years.
Note that the capacitor doesn’t fail at the lifetime. That’s when the capacitor’s value may creep more than 30% of nominal. None of the electrolytic cap values in the Mk II are anywhere near that critical.
“Back in the day” most caps were rated for, say 1000 or 2000 hours at 85C. This would give five years in this same environment. (2000 hours at 40C instead of 85C is 5.17 years.)
Also the electrolytic caps are spaced a good distance from the heat sources so they should never get to 40 or 50C.
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I have had my lid off for a couple weeks now and the internal temperature is actually cooler then the MK1.
Thanks, Ted. Given the quality of electronic components today and good design principles, I guess that’s what I should have expected. Settles the issue for me.
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