Re: From an audio forum... FR4 question

On Fri, 11 Nov 2005 23:41:27 +0100, "Fred Bartoli"
<fred._canxxxel_this_bartoli@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

>
>"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> a écrit dans le
>message de news:qv2an1hn73dp8ac0ommfeh1kf4jh7bbnvv@xxxxxxxxxx
>> On Fri, 11 Nov 2005 20:28:35 +0100, martin griffith
>> <martingriffith@xxxxxxxxxxxxx> wrote:
>>
>> >I found this
>> >
>> >"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."
>> >
>> >
>> >any comments?
>> >
>> >
>> >martin
>>
>>
>> Totally bogus. Good thing "sounds" is in quotes, indicating the
>> effects can only be discerned by audiophools. I work with signals far
>> below audio levels, and FR-4 is fine.
>>
>> The worst features of FR-4 are its horrendous temperature coefficient
>> of dielectric constant and its small capacitive "hook", neither an
>> issue for audio.
>
>
>I've already searched info about this "hook" but found nothing. Do you have
>some info/pointers?


Some old Tektronix appnotes referred to the dielectric absorption of
FR-4 as "hook" because it made ugly overshoots and undershoots on the
rising edges of scope waveforms. FR-4 makes nasty capacitors, with
lots of DA and TC in the +900 ppm/k range.

John
.

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