And the winner is... Elizabeth!
Just talked with Kent at Pass Labs. Nice guy. Kent said that, by removing the lid, the temperature inside the chassis falls (that much is obvious). When the internal temperature sensors detect falling temperature, the amp increases the bias. That's why the bias needle went from 11 o'clock to 1 o'clock. And when the bias goes up, the cooling fins get hotter. So...
lower internal temp -> increases the bias -> hotter cooling fins
...and...
higher internal temp -> decreases the bias -> cooler cooling fins
Makes total sense.
Here's the most interesting part: Increasing the bias also improves the sound quality. A LOT. Kent didn't seem surprised by that. He said that the bias level is determined by weighing various considerations, including not only sound quality but also heat output in the average domestic environment and safety issues associated with very hot cooling fins.
I mentioned to Kent my intention to leave the lid of the amp off. He wasn't too supportive of the idea. Something about lethal voltages. As far as the amp's lifespan, Kent said that running the bias that high isn't bad for the amp, since the parts have considerable temperature tolerances. In other words, I shouldn't worry too much about shortening the lifespan of the amp. And I'm not.
The issue of death by electrocution is a bit more serious. I'll have to weigh the value of better sound quality against the value of living. The amp is located high in a closet, so it would be a very bizarre set of circumstances that would lead me to reach up over my head and stick my hand in the amp while it was on. But I suppose anything is possible. Good judgment tells me to put the lid back on. Bad judgment tells me to enjoy this unexpected "upgrade."
Bryon
