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What does microphonic tube sound like?

I have this strange problem since I replaced my old SS preamp to a tubed preamp. Some of my CDs when played through Linn Unidisk sound scratchy. There is this annoying scratchy echoy sound throughout the CD and I can't listen to them. But the same CD, played through my PS1, sounds fine. I had both Linn and PS1 with the old SS preamp, and I didn't have this problem with that particular CD in either player.

I think the problem is with either the CD (bad press?) or the new tubed preamp. The current hypothesis is that the more extended sound from Linn is triggering preamp to misbehave and produce the scratchy sound, because the sound from PS1 is softer in extreme frequency ends. I don't know if what I'm hearing is microphonics, but if it is shouldn't it happen to all the recordings?
jylee
shadorne's avatar
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shadorne
7,467 posts
 
I expect The Linndisk is overdriving the new preamp and this produces distortion - especially on a modern "loud" CD but less so on a CD made in the late 80's...

The PS1 may simply have lower output and therefore it does not overdrive your new pre.

Microphonics are a bigger problem with power amplification rather than the smaller tubes in preamps - of course it is always a drawback of tubes and it is best to place tubes away from a corner and preferably in another room if you listen loud.
digsmithd
913 posts
 
You tap the suspect tube and if the filaments buzz or make noise youve found your culprit.
mofimadness's avatar
mofimadness
4,943 posts
 
"Microphonics are a bigger problem with power amplification rather than the smaller tubes in preamps"

Really? I have owned hundreds of tube amps and preamps and phono stages and have NEVER had a microphonic tube in an amplifier. I've had plenty in preamps and phono stages.

Huh, you learn something everyday...
entrope
482 posts
 
An annoying buzz, hum, squeal or whine much like a spouse.
jea48
4,323 posts
 
This guy does a good job of explaining it.

My experience with a bad microphonic 6922 tube was as he described with a little ringing sound thrown into the mix.

Tap on top of your preamp lightly with two extended fingers. If you can hear your tapping through a speaker/s you have an excessive microphonic tube/s.
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