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Dac acts like a microphone

I replaced the stock tudes in my Audio Note Dac to used Amperex 6922 tubes. When I powered the unit up there was a strange sound (as the sound of an AC unit running) coming from the left speaker. I took the tubes out and put them back in. The dac was now picking up sounds from my tapping the dac through the speakers. I got the feeling that I could sing into the dac and it would act like a microphone. As the tubes got hot, and two hours of running, I had no problems. Will this happen again because the tubes are bad?.

Thanks,
Gary
128x128glory
jea48
4,279 posts
 
Sounds like a bad microphonic tube. If by chance you just bought them from a dealer send him an email. Most dealers will replace microphonic tubes. If they are a matched pair he should replace both. If you bought them on Ebay, well....
glory's avatar
glory OP
1,614 posts
 
Jea48,

I bought them on Ebay. Why do they sound good now?. If it is a bad microphonic tube will it show itself again?

Gary
rwwear
2,847 posts
 
All tubes are microphonic. I find that is best not to tap on equipment especially while it is playing.
aball
2,016 posts
 
I solved microphonic tubes by using Herbie hal-o tube dampeners. Problem never came back so I recommend them.
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