Pass Labs XA30.5 Fuse Issue/Question

Are you sure there are no strands of wire touching at the speaker terminals?

Certain the fuses are the correct rating? You can read it on the metal end caps.

Can you run it at a low level for a period of time? I don't know the circuit but it's possible that it might bring on more transistors as power output is increases, and something there has failed.  

@noromance 

Good thought about the short on one side of the speaker cables or another. If not, sounds like time to ship to Pass.

Likely.. but do call Pass Labs first!

If you recently purchased the amp, I would call The Music Room and ask for help.

+1 on calling pass labs and the music room. I would start with pass labs to gather some data points for the conversation with TMR.

Question - do you have the amp connected to the wall or to some sort of power conditioner/strip?

You should play the amplifier through another set of speakers before calling the seller or Pass. Tripping a mains fuse at higher playing volumes makes the Harbeths the prime suspect.

" I tested the amp with a different set of speakers and a different source/preamp, but the same issue occurred every time."

You should return the amp and get a refund from TMR. It sounds like that Pass is a lemon!

The meter on the Pass XA amplifiers measures bias current. Under normal circumstances it should barely move at all, and then only when playing very dynamic music at high levels. If the amp was shorted it may have incurred permanent damage and so exhibit the same behaviour with different speakers. Pass gear is extremely reliable but no product is infallible so it may also be a component failure within the amp. In any event, it should be taken back to the supplying dealer for investigation.

Pass labs is very user-friendly...do not hesitate to call them

Sending it back to the music room for a full refund would be my only move. Done it before with zero issue as long as it's done within the return period. 

Thanks everyone for your responses! After learning the hard way in my early audiophile days, I’m super careful about avoiding shorts and triple checked all connections, so I don’t think that’s the culprit here.

@noromance, I think you zeroed in on something important - the amp is totally stable at low levels and will run indefinitely in that state. It only begins acting crazy when pushed to higher levels - your inference about a problem with one or more of the transistors coming online as power increases sounds very plausible!

@audphile1, the amp is connected to a Core Power Technologies Equi=Core 1800 conditioner.

I’ll be calling TMR today to get their read on the situation and sounds like the amp going back might be the most likely outcome. I appreciate everyone’s input.

While Pass Labs are great to work with, calling TMR should definitely be your first step.  They are pretty good about this stuff and should pay for the return shipping as well.

All the best.

the output stage cannot generate sufficient current meaning that either power transistor replacement or filter caps or both.

Problem resolved and, in what is probably a surprise to nobody, the issue was 100% foolish user error and not at all to do with any fault in the amp.

I had completely forgotten (despite having owned a number of First Watt amps with the same characteristic) that the XA30.5 is a balanced output device with both terminals live. I stupidly had an REL sub hooked up via high level connection and managed to overlook the ground terminal Pass supplies for these purposes.

As soon as I rewired the sub correctly, the problematic behavior disappeared, the amp stopped eating fuses and is humming along happily as ever.

Thanks everyone for the advice - and mea culpa!

Interesting adventure! Congratulations!

ozzy