2. amps-preamps
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Thumping sound in right channel of Amp

I own a Cayin A88T for almost a year. I would say it sees moderate use. Recently I am noticing a rather loud thump in the right channel after the initial 30 second warmup. This can happen a couple of times during the first 10 minutes of having turned on the unit. After this time the unit sounds fine. I haven't altered anything on the unit which I bought new. From what I have been reading tube rolling is common practice with the Cayin but this is something totally new to me. I must thank Danlib for the detailed instructions he e-mailed me on biasing the unit.
Should i be concerned about the initial thumping, Will tube rolling solve the problem?
flyfisher
3 responses Add your response
herman
2,253 posts
 
The fact that it just started doing it after a year AND it only does it in one channel clearly indicates that something is wrong.

Are you sure it is the amp thumping and not something before it? Swap the left/right inputs and see if it moves.

Sometimes this is caused by a tube arcing. Darken the room, watch closely, and see if a tube flashes during warmup.

If not, swap tubes from left to right. If the thump moves you have a defective tube. If it doesn't move you have a defective amp.
flyfisher OP
46 posts
 
I tried it this morning with nothing else on just to make sure it wasn't another component but the same thing happened. I just swapped all four tubes on the right for their exact opposite on the left. No thump. I only left the amp off long enough to do the swap so I am going to shut down for a couple of hours and see what result I get.
flyfisher OP
46 posts
 
Once I swiched the tubes I opted to check the bias( I should have put them back the way they were originally) Nevertheless,The bias was fine on the left channel but very low on both pods in the right. I adjusted all to .4vdc and haven't heard a pop. I also noticed that the initial thump at start up is not as pronounced.
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