2. amps-preamps
  3. 1267215854

Why are my mosfet fuses blowing?

I have a Classe CA-200 Power Amplifier/200 watts per channel into 8 Ohms (side heat-sink version)which is driving a pair of Thiel CS2.3s with upgraded coaxial tweeter/midrange. Sound is very good. I listen at relatively high volumes and recently (over the last year) the amplifier is getting hot within 60 to 90 minutes of listening and the mosfet fuses (2AG 1/2 PT, 1/2 amp fast blow) have been blowing. Do I need a higher powered amplifier to listen at high volume? Should I look for a used CA-200 and use one to drive each speaker (700watts into 8 Ohms)? Thanks.
bcarr38

Showing 2 responses by herman

herman
2,280 posts
 

You are blowing the fuses for the driver stage
The Classé CAM200 equipped with a rail currents sensors to protect the output drivers under extreme condition such as short output, and Mosfet fuses (2AG 1/2 PT, 1/2 amp fast blow) to protect the Mosfets, which are used as pre-drivers for the output stage of the amplifier.

That leads me to believe the problem is with the amp, not the speakers or the volume. There is no reason for the driver stage fuses to blow unless the amp has a problem like one of the output transistors breaking down when it gets very hot.

Have you contacted Classe for their opinion as they suggest in the manual?
IF IT APPEARS THAT PROTECTION FUSES DID BLOW, CONTACT YOUR LOCAL DEALER. DO NOT TRY TO CHANGE A BLOWN FUSE. REPLACING A FUSE WITHOUT CHECKING FOR COMPONENT FAILURE COULD RESULT IN FURTHER, SERIOUS DAMAGE TO VITAL COMPONENTS IN YOUR AMPLIFIER. CONTACT YOUR LOCAL DEALER or Customer Service at the Classé Audio, Inc ---(514) 636 63 84.


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herman
2,280 posts
 
A short in the speaker should be audible at moderate levels; one or more of the drivers would not be working. It is also an unlikely scenario. Failures in speakers are typically something burning up because they were over driven. This results in an open, not a short. It is possible that something is physically touching inside that causes a short but you should be able to put your ear up to each driver and see if it is working.

The other simple test, assuming you have access to another set of speakers, is seeing if it blow fuses on another set.

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