2. amps-preamps
  3. 1221700245

Tube preamp noise

I acquired an all tube preamp, and one thing I immediately noticed was that the preamp is super sensitive to any external impact, however small may it be. With a gentle tap on the cover of the preamp is echoed and heard on the speaker even when the volume is set to minimum. Same thing when I tap on the audio rack, other equipments (power amp, cdp, turntable), and even on the floor.
It is just like the sound you would hear from the PA speaker when you tap on a microphone.
Is it common on certain preamps?
Anybody experienced this?
128x128ihcho
darkmoebius
899 posts
 
It would help to know which particular preamp you got and what types of tubes it uses?

Some types of tubes are more "microphonic" than others. Other times it's just a bad tube and a replacement is all that's needed. Beyond that, it's the implementation or construction of the component.
tvad
9,467 posts
 
You're experiencing a microphonic tube (or tubes). Hopefully, it's isolated to one channel. You can often find the bad tube by gently tapping on each tube's glass bottle with a rubber pencil eraser. The bad tube will be obvious because it will display the microphonic effect louder than the other tubes.

At least this has been my experience.

What type of tubes does your preamp use?
ihcho's avatar
ihcho OP
329 posts
 
Many thanks.
I will try to find a bad tube. Well, one of my friends is a strong bias on tubes and almost forced me to buy a tube preamp when I was about to upgrade, but I am not new to tubes. I may be forever like that. ;-(

Anyway, thanks for your help. My preamp uses 6SN7.
I will try to find a bad tube and replace with another, and see if the problem goes away.
tvad
9,467 posts
 
6SN7. That explains a great deal.

I have owned more microphonic 6SN7 tubes than any other tube type. Many of them have been the highest priced, most sought after varieties.

Having said that, the one 6SN7 preamp I owned sounded fabulous when the tubes were all good.

Good luck. I'm sure you're going to love the preamp when the tube situation gets sorted out.

For excellent quality, guaranteed 6SN7 tubes, I suggest contacting Andy at Vintage Tube Services.
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