Is my Pass amp overheating?
...you have the issue of both channels being equally biased. Herein lives everything you're going to love or hate about a particular amp. Without it you have no channel balance, stereo image, frequency extension, or the ability to determine low level resolution, speed, or any other sonic parameter.Can you say more about this? I'm not challenging you, I just don't quite understand how it works. How do differences in L/R bias level result in, e.g., differences in low level resolution? bc |
I can't explain technically why this is. Others in the know could weigh in here and describe how electrical behavior equates to sonic outcome in this matter. But I learned early on in this hobby that channel balance is absolutely essential to realizing all of the performance attributes a given amp boasts on it's spec sheet as they relate to your ears. And I'm not referring to the balance knob on your pre. Perceived resolution diminishes simultaneously with the degradation of stereo image. The quality of the stereo image is dependent on how accurately one channel is biased with the other. Remember the definition of "stereo". The accurate placement of sound sources in space. When you don't have this, resolution can't help but suffer since amplitude is not identical on both sides. Probably because quiescent current is lower in one channel and therefore those power transistors are operating with less output. If you are not experiencing "pin point" imaging, regardless of room acoustics, then the bias is off. Any basic amp is capable of this when functioning properly. Not only properly, but potentially better than spec. By the time an amp has been transported to the show room floor, enough tossing around has taken place to knock it off kilter if it ever was right on. You can fool yourself into thinking you're listening to stereo when all you really have are right and left sources. Frequency extension is affected by accurate channel balance in the same way. Especially the bottom end. It is a very good indicator of whether you're in the ball park. |
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 |
