First there is a mountain,
Then there is no mountain,
Then there is...
Then there is no mountain,
Then there is...
Is my Pass amp overheating?
The amp is an XA30.5.
Yesterday I was doing some tinkering and the amp was turned off for a couple hours (unusual for me). When I was done, I sat down to listen while the amp was still cold. To my surprise, it sounded BETTER than I'd ever heard it.
The amp is Class A, so according to conventional wisdom, it needs to warm up before sounding its best. Yet it definitely sounded better BEFORE it warmed up. So I'm wondering if the amp is overheating. To test this, I took the lid off the amp. Three things happened:
1. At idle, the bias needle moved from 11 o'clock to 1 o'clock (unprecedented).
2. The cooling fins became much HOTTER (not cooler, as I would have expected).
3. The sound quality of the amp remained "improved" even after several hours.
Can someone please explain what's going on?
Thanks,
Bryon
P.S. The amp is in a closet. But I don't think that's the problem, for the following reasons: The amp is on the top shelf of an equipment rack, so there is two feet of open air above it. There is a large fan in the ceiling of the closet that sucks air and sends it through a duct to the outside of the house. So the closet stays very close to the temperature of the rest of the house. Also, I can reproduce all the effects described above with the closet door open.
Yesterday I was doing some tinkering and the amp was turned off for a couple hours (unusual for me). When I was done, I sat down to listen while the amp was still cold. To my surprise, it sounded BETTER than I'd ever heard it.
The amp is Class A, so according to conventional wisdom, it needs to warm up before sounding its best. Yet it definitely sounded better BEFORE it warmed up. So I'm wondering if the amp is overheating. To test this, I took the lid off the amp. Three things happened:
1. At idle, the bias needle moved from 11 o'clock to 1 o'clock (unprecedented).
2. The cooling fins became much HOTTER (not cooler, as I would have expected).
3. The sound quality of the amp remained "improved" even after several hours.
Can someone please explain what's going on?
Thanks,
Bryon
P.S. The amp is in a closet. But I don't think that's the problem, for the following reasons: The amp is on the top shelf of an equipment rack, so there is two feet of open air above it. There is a large fan in the ceiling of the closet that sucks air and sends it through a duct to the outside of the house. So the closet stays very close to the temperature of the rest of the house. Also, I can reproduce all the effects described above with the closet door open.
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- 31 posts total
07-07-12: BtselectI happen to own two 120mm Noctua fans already, which were formerly used to cool a Class A amp that I no longer own. So the idea of using fans has not failed to occur to me. As far as making mountains out of molehills... Using the fans to cool the amp is NOT sufficient to change the amp's bias significantly. I've tried it. The amp's thermal vents are both narrow and few. The lid must be either removed or replaced. If the lid is removed, the amp is exposed to a significant amount of RFI, because there are 3 switching mode power supplies within 3 feet. I've taken extensive steps to reduce the effects of RFI in my system, which were discussed at length in another thread. Removing the lid permanently has the potential to undo many of my efforts on that front. Not to mention, the fans themselves produce a considerable amount of RFI, so the idea of sticking two additional RFI sources directly above and below the amp isn't that appealing to me. Hence my decision to fabricate a mesh lid, which allows for much greater circulation than the stock lid (and therefore higher bias setting), while still protecting the amp from RFI. So I hope you can see that the situation is neither a mountain nor a molehill, but something between. Bryon |
Hi Bryon Thank you for posting this thread, it lead me to try something a bit different to try to achieve a similar result. I can not remove the lid or try a fabricated one like you designed with copper mesh and aluminium (very impressive by the way)... as I have roadworks near my house causing a lot of dust & dirt in the air. *** So I tried ... elevating my amp. *** Aim was to improve better/cooler airflow from under the amp, thus improving the chimney effect, hopefully to achieve a similar result to you. My amp is similar to yours , though it is an integrated, the Pass Labs INT-30A. I was in the hardware store and found 3" high door stops made of stainless steel (also 3" diameter). I purchased 4 of them for a total of $12 as an experiment. Placed under the existing feet of my amp, it increase the space under the amp from 1" to 4". I have also noticed that the heat sinks now run hotter and a improvement in sound (it is minor, though easily heard). Also, thank you for posting your system. I have Focal Micro Utopia Be and reading your system was one of the things that gave me confidence to try and buy a Pass Labs 30wpc Class A integrated amp a few months ago. John |
12-22-12: Duke40You are welcome, John. Glad you figured out a solution that worked for you. Also, thank you for posting your system. I have Focal Micro Utopia Be and reading your system was one of the things that gave me confidence to try and buy a Pass Labs 30wpc Class A integrated amp a few months ago.Again, you are very welcome. Happy listening! Bryon |
- 31 posts total