Re: From an audio forum... FR4 question

John Larkin wrote: 
I submit that if you open up your amp and start tapping parts with a
pencil, the loudest noise you'll hear is the sound of parts being
tapped with a pencil. To solve this particular problem, quit hitting
parts with pencils.

What if the "tapping" is caused by environmental factors, such as road vibration, acoustic waves from loudspeakers? Do you just stop the vehicle by the side of the road? Tell the musicians using your amplifier at the concert to stop playing so loudly?

My NMR gradient drivers have a couple of PPM noise, dc to 50 KHz, and
use regular surface-mount parts on FR-4, with lots of noisy fans.
Aside from pure semiconductor and resistor noise, the next biggest
hazard is magnetic loop pickup from fields leaking out of transformers
and fans.

Sounds like your NMR machine must be a large heavy device, mounted in a quiet building somewhere. No worries, then.

How will a microphonic cap make hissy, buzzy audio? 

Maybe you missed my earlier post:

Ref:  Linear Tech AN83, page 14:

"A piezoelectric device generates voltage
across its terminals due to mechanical stress, similar to
the way a piezoelectric accelerometer or microphone
works. For a ceramic capacitor the stress can be induced
by vibrations in the system or thermal transients. The
resulting voltages produced can cause appreciable amounts
of noise, especially when a ceramic capacitor is used for
noise bypassing. A ceramic capacitor produced FigureÊ B4’s
trace in response to light tapping from a pencil. Similar
vibration induced behavior can masquerade as increased
output voltage noise."

I'm trying to be helpful.

mw
.

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