Is my Pass amp overheating?

Update...

I built a new lid for my amp out of aluminum and copper mesh. You can see a picture of the lid here. You can see it installed here.

The copper mesh is electrically continuous both with the lid and the chassis of the amp, which improves the mesh's RFI rejection, according to the folks who sold it to me.

With the new lid installed, the amp's bias needle is at 12 o'clock at idle. That is down from where it was when the lid was off, but up from where it was when the stock lid was on. So...

-With stock lid: 11 o'clock.
-No lid: 1 o'clock
-My new lid: 12 o'clock

This makes sense, since the copper mesh is only 70% open, and the lid's aluminum frame narrows the opening somewhat. So it's a little hotter inside than it was without the lid on.

When I get a chance to sit down and listen, I will report back the results.

Bryon

Just realized that I never reported back the listening results after installing the aluminum and copper mesh lid that I installed on my Pass amp.

As I mentioned in my last post, the mesh lid DECREASED the amount of heat inside the chassis relative to the stock lid but INCREASED the amount of heat relative to no lid. As a result the bias of the amp is highest with no lid, lowest with the stock lid, and half way between the two with the mesh lid.

The listening results are these... IMO, the amp sounds best with no lid, i.e. at the highest bias setting. At that setting, the instrument timbres are the most realistic and the overall presentation is the most musical. Next best is the mesh lid, i.e. at the middle bias setting. Then the stock lid, i.e. at the lowest bias setting.

Although no lid sounds slightly better than the mesh lid, it makes me a little nervous leaving the lid off permanently, even though the amp is in an equipment closet.

On a slightly different subject, it's worth pointing out that the amp must be fairly impervious to RFI, since the addition of the copper mesh, which reduces RFI significantly, was less beneficial to sound quality than the difference between the no-lid bias setting and the mesh-lid bias setting. I suppose that's because of Pass's "Super Symmetry" design? Or maybe that's just marketing? I don't know.

In any case, I'm still pondering whether to go with the custom lid or sans lid. I wish there were a way to turn up the bias manually.

Bryon

You just hit the nail on the head Bryon.

Hi Csontos - I just read your thread on DC offset and bias. Very interesting.

You just hit the nail on the head Bryon.

Are you saying that there's a way to manually adjust the bias on my XA30.5? According to Pass, the autobias on the amp is regulated by internal chassis temperature, which is consistent with my findings comparing the stock lid, the mesh lid, and no lid. In light of the amp's autobias, is it unlikely that the amp also has adjustment pots to manually set bias?

Bryon

I'm not familiar with your particular amp. What I don't understand is why manufacturers don't incorporate user adjustable bias controls in ss amps the way they do with tubes. It's especially relevant in your case where the tolerance in the auto-bias prevents the amp from ever achieving pin-point accuracy. You've just verified where the ultimate potential of your amp lives, as with any ss amp. At least with a fixed bias you can fiddle with it till you find it, not so with yours. If you could, this thing would knock your socks off!