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Weird Amp Thing


Sugartune

Question

Weird issue, or maybe not but how I came across it kinda was.

I have a Revv D20 (20 watts 6v6s with Two Notes Torpedo built into it) on my computer desk, running into my DAW and also out to a cabinet behind me. 

Just now, I was playing, put my phone down on my desk and heard a much louder thump than expected. Turns out is coming out of my cabinet behind me. Guitar is muted through a tuner and volume rolled back all the way. So it's not that.

I do it again just to confirm. It seems to be the phone making the amp do that. Any tap on the desk or amp itself, for that matter.

Guessing that suggests a microphonic tube? Maybe something else potentially? 

What do you experts say?

 

Thanks in advance.

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So, if you tap the desk with items besides the phone, does it still happen?  If you've got the gain up, even non microphonic tubes, particularly preamp tubes, can still transmit a thump through the speaker if you tap them.  Microphonic tubes will "ring" if you tap them.

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5 minutes ago, tbonesullivan said:

So, if you tap the desk with items besides the phone, does it still happen?  If you've got the gain up, even non microphonic tubes, particularly preamp tubes, can still transmit a thump through the speaker if you tap them.  Microphonic tubes will "ring" if you tap them.

It also happens with anything other than the phone, yes. 
 

I had minimal gain. But the master was up loud and clean. 

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Just now, Sugartune said:

It also happens with anything other than the phone, yes. 
 

I had minimal gain. But the master was up loud and clean. 

Oh, no ringing. Just the thump coming through the speaker.

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Something is reacting to the impulse created by the thumping. The most likely candidate is a tube, since they are simple amplifying devices relying on a physical structure to operate correctly. A disruption in the structure, like an impulse loading transferred from the tube base could wiggle the electron stream enuf to cause a noticeable sound effect. It might not even be a bad tube, just a situation where the impulse is transmitted or possibly amplified by a resonance in the combined system of physical entities.

I hate mornings.

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Thank you! It doesn’t seem to cause any other issues at the moment. 
 

I’ll keep an eye and ear on things in case they change or worsen. 
 

much appreciated 

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I agree with JGale.  Could easily be a loose tube / bad connection as opposed to microphonic. 

Take 'em out and put them back in.  I fixed the climate control on one of my cars by taking the fuse out, looking at it funny, and then putting it back in.

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If'n you're going to take them out / put them back in - highly recommend giving the pins a shot of Deoxit (or similar, contact cleaner) and inserting / removing a few times on each.  It cleans the sockets and pins and makes everything clean and happy.

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