Microphonic Capacitors??

[chinrest]

I don't know if I've ever tapped on coupling caps before... but when I tap on this one (Mallory 150 series, .047uf, Fender tone stack), it goes 'bump.' If the volume and bass controls are cranked, it goes 'BUMP.' If I tap the leads, there is no bump--only when I tap the center of the cap.

Is this normal?

[Enzo]

Lots of caps are microphonic. Is it causing trouble? or is it just something new to you?

[lowell]

i've wondered the same thing. someone once told me that by tapping on them w/ the volume cranked that any of them that make noise should be replaced... however brand new caps even almost always make a sound when tapped.

[chinrest]

Yes, it's new to me, and no, I don't think it's causing problems. It seems to be doing its job. I just wondered if it could be contributing noise to the preamp.