Re: From an audio forum... FR4 question

On Sat, 12 Nov 2005 16:52:33 GMT, mw <mw@xxxxxxxxxxxxx> wrote:

>> "The FR-4 works very well in most audio applications. However, it is a
>> very hard material and has a tendency to vibrate. This might cause
>> tiny current changes in the components on the board, which, especially
>> in very low level circuits like MC phono preamps and microphone
>> preamps can cause unwanted ?sounds?. Teflon base-material, which has
>> been developed for HF circuits, is much less prone to vibration.
>> Consequently it is very much preferred for low-level circuits."
>
>I am not familiar with Teflon's vibration properties, but it is safe to
>say that ceramic caps mounted on FR-4 that is subjected to vibration
>will generate piezolectric effects that may distort high gain audio signals.
>
>There are other capacitors more tolerant of vibration.
>
>mw


I had a pll running at 155.52 MHz with a narrowband (2 khz) loop, on a
VME module. Whenever one pulled an SMB test cable out of its
connector, the loop briefly lost lock. After some tapping and bending,
we found it was the expensive Vectron crystal oscillator, not the
caps. We designed some tiny springs to isolate the oscillator can,
made it wobble like one of those gooney-head dolls you see in the
backs of cars.

"Safe to say?" I can't imagine any significant pcb microphonics in an
audio system in any real-world sense. More audio nonsense.

John

.

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