bias current

[rabident]

I've had great support from Classe over the years, even on my 10 year old cav-75 long since out of warranty. I had an issue with it over heating and triggering the protection circuits (and occasionally popping a fuse in the process). Classe said bias current can drift over time and they had trim pots to adjust. My dealer made the adjustment and now the amp runs very cool.

But I started thinking, doesn't bias current and the heat output reflect how long the amp stays in Class A mode? I wonder if by trimming the pots so the amp runs cool I've given up some sound quality in the process.

Also, unrelated, the amp "squeals" a bit when I turn it off. When there's a source present you can actually hear the content playing, presumably from the remaining charge in the caps. The distortion picks up as it runs out of juice. I was wondering if that distortion is essentially the amp clipping due to lack of power and if it presents any danger to my diamond tweeters.

[wxmanunr]

When AMP is Turned Off

I see this with my CAV-150, also. I'm pretty sure it is normal. Just don't send a signal through it when you are turning it off.

wxmanunr

[Glen B]

But I started thinking, doesn't bias current and the heat output reflect how long the amp stays in Class A mode? I wonder if by trimming the pots so the amp runs cool I've given up some sound quality in the process.

Yes, the bias current affects the amount of watts output in class A. The calculated class A output of the CAV-75, based on its factory specified bias current of 120mA is approximately 100mW into an 8 ohm load/50mW into a 4 ohm load. The dealer would have adjusted the bias to the specified level which Classé feels is appropriate, so I would not worry about it. Overbiasing the amp would make it run excessively hot, while bringing no additional benefit.

Also, unrelated, the amp "squeals" a bit when I turn it off. When there's a source present you can actually hear the content playing, presumably from the remaining charge in the caps. The distortion picks up as it runs out of juice. I was wondering if that distortion is essentially the amp clipping due to lack of power and if it presents any danger to my diamond tweeters.

The CAV-75 and CAV-150 do not have output relays that disconnect the speakers when the amp is turned off. You're hearing the input signal being amplified as the main filter caps run out of juice, a normal occurrence with such a design. There is no danger to your speakers. As mentioned above just shut off your source before turning off the amp.

[Srrndhound]

The CAV-75 and CAV-150 do not have output relays that disconnect the speakers when the amp is turned off. You're hearing the input signal being amplified as the main filter caps run out of juice, a normal occurrence with such a design. There is no danger to your speakers. As mentioned above just shut off your source before turning off the amp.

My CAV-150 whistles its little goodbye tune even when there's no input signal. It's actually a low-level oscillation.

Also, unrelated, the amp "squeals" a bit when I turn it off. When there's a source present you can actually hear the content playing, presumably from the remaining charge in the caps. The distortion picks up as it runs out of juice. I was wondering if that distortion is essentially the amp clipping due to lack of power and if it presents any danger to my diamond tweeters.

Yes, as the supply rails collapse, the signal is increasingly clipped. The level is so low it will not damage anything.