2. amps-preamps
  3. 136120-97064

Pass labs X250.5 cracking noise

Hi all, recently bought a used X250.5 from a dealer on audiogon. Really happy with the SQ. The amp makes a crackling noise after powering down. Its a few cracks/pops - very intermittent and then it subsides. Spoke with Pass engineer and he assured me that the noise was coming from thermal contraction of heat sinks etc after normal operation. This weekend I noticed that the amp made cracking noise during warm up too. Again this is one or two and then after the amp warms up - i dont hear any more pops. Or i guess the sound from speaker masks it perhaps? I did pause music and noticed the amp for about 30 minutes and no cracking/popping noise during that period. Anything I should be worried about? I'll call Pass again this week - but wanted to see if there were any thoughts?
pistha

Showing 5 responses by pistha

pistha OP
31 posts
 
Hi John, Thanks - I pretty much do the same thing - Amp powered on last and powered off first. The noise I refer to is a mechanical popping noise (like a single popcorn bursting) from the amp - not the speakers. 
pistha OP
31 posts
 
George, I dont drive them hard - I dont think i ever exceed low 80db spl. I also notice that the bias meter doesnt ever leave class A for my listening level. I drive a pair of wilson sophia 3s. I dont think the sophias swing wildly in impedance either (per wilson). I've gota be honest - dont know what a high phase angle speaker is! I'll give the temperature measurements a shot - thanks for the suggestion!

Ragav 
pistha OP
31 posts
 
Called Pass and the engineer assured that this was just the heat sink making the noise from thermal expansion and contraction. Apparently the heat sink can be more tightly secured with a couple of bolts behind the faceplate. 

btw George - i measured the temperature on the fins and they were reading 100F & 110F on left and right sides. I mentioned this on the call with Pass and they didnt think it was a wild swing. 

Now i know this is a minor annoyance at best - am not going to do anything but enjoy music! thanks everyone.
pistha OP
31 posts
 
This is fine one side could be in a draft more than the other no biggie.

I heard Pass mention the same thing about draft - silly me - i assumed he was talking about air draft from a/c vent! Now that you mention - what exactly is draft in the sense you mention above? 
pistha OP
31 posts
 
@tonyptony - i've moved on! the cracking noise from the x250.5 doesnt bother me any more. It only happens during the first 10 mins and then after powering down the amp. @fabio3181's problem seems to be unrelated to thermal expansion - i wouldnt expect the pass preamps to have any measurable thermal contraction/expansion. 
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