Microphonic from Vacuum Tubes?


HI,  I have a question regarding microphonic from vacuum tube.  I have a Cary SLP-05, and I've changed the output gain tubes to some NOS RCA, and also recently purchased a pair of Linlai for the balanced buffer stage.

I now occasionally hear a loud pop in the music.   It doesn't happen very often, but when it does, it is quite loud.   This happens when I am streaming digital music, so it can't be those occasional pops you hear from vinyl.  

Can someone tell me if this loud pop possibly caused by microphonic in my tubes?  if so, how do I track down which tubes?   My guess there is no easy way but change one tube at a a time, which can be extremely time consuming.   Also I don't own a tube tester.  I wonder that would help tracking it down.

Also I read something about vacuum tube damper rings,  would that help calming down possible microphonic?

I still  consider myself a newbie in tubes,  so any hep will be appreciated.  Thanks very much.

128x128xcool

As @atmasphere said, it might not be the preamp that is causing the pop.

What are you running for an amplifier?

Generally speaking, when I have had a tube going noisy in my preamp, I could find which one it was by lightly tapping it with my fingernail or the equivalent. Something you could do is to put the tubes back in it, that Cary had in it when you bought it, and see if the pop is replicated. Maybe just put the positive phase buffers in first, and then if you still get the pop, try the input buffers. Or vice versa.

Hi @larryi ​​​​@atmasphere,  let me try to answer your questions.

I don't usually play music at loud level anymore.   I want to preserve my old ears from more hearing loss. 😀   It is usually played at below 70 db level.  

The noise does seem random, and it's coming from one side.  I've only heard it maybe 3 or 4 times, and I think it had happened to either the left or the right channel, but not both.

I just did the tapping test that @larryi suggested, and I hear no pops.

I don't think I've heard it at a very low volume, but then again, It has only happened a few times, so I don't recall what the volume level was at the time, but I think it was probably at my usual listening level of somewhere in the 60 to 70 db range.

I don't know if the problem is the preamp, but it is my newest component.  I've never heard this loud pop before I bought the tube preamp.  So that is my suspicion.   The pair of Linlai 6SN7 tubes are my latest purchase, and I wonder if that can be the culprit. 

Thanks!

@xcool OK- keep in mind to make no assumptions. That can lead you on a wild goose chase.

The first thing to do is swap the interconnect cables left for right at the amplifier inputs and see if the problem moves.

If yes => the cable, preamp or source is on the hook

If no => the amplifier is the problem.

So do that and get back to us.

Or, if the problem moved, the next thing to do is swap the connections from the source at the input of the preamp.

If the problem moves its the source or its interconnect cable.

If the problem stays put then the preamp is on the hook.

If you get to that point then you swap tubes from one channel to the other, a pair of tubes at a time. Between each swap you play the system until you can determine which channel has the bug. If it moved you know which tube is bad, if it didn't then you proceed to the next pair of tubes and repeat the process - do this until the problem moves and then you've located the bad tube.

Good Luck!

Thanks @atmasphere for your instructions.  The problem is that I think I've heard the pop from either left and right channel before, but not at the same time.   So the problem doesn't seem to be specific to a single channel.

I sure hope that this is not an issue with my Cary preamp.  I've had enough problems with it since I bought it about 7 months ago.  😀