Is my Pass amp overheating?

Hi Alan. Here's an except from the article that Al linked...

In general, apertures should be smaller than L = l/50 [where L=length of slot (in meters) and L ³=w and L >> t and l = wavelength in meters]. To achieve acceptable attenuation values at a frequency of 1,000 MHz (not unusual for high-speed digital devices) apertures should not exceed 6 mm.

Actually, it's quite remarkable that mesh with apertures up to 6mm provides effective RFI protection, since 6mm apertures look like this. That mesh is 77% open and would provide more than enough ventilation.

In fact, I was thinking about taking Elizabeth and Al's advice and choosing something more like this, which has 1.3mm apertures and is 67% open.

Thanks Al and Elizabeth for your help. Very appreciated!

Bryon

I would think small holes would provide protection as that is how a microwave oven glass door works. We see through the small holes and the waves can't penetrate the screen.

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.