From an audio forum... FR4 question

[martin griffith]

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

 

[Keith Williams]

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?

Just use one of these:

http://www.machinadynamica.com/machina27.htm

 

[GregS]

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

In phono circuits, even the cable can vibrate and cause effects. If you grab
them and move them about, you will hear them. Probably much more serious than circuit board effects.
I disagree with the statement about vibration stiffness. There is a difference
in stiffness, but TFE generally is soft and damps vibration more.

greg

 

[John Larkin]

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.

John

 

[martin griffith]

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.

John

Hi John, I agree with you, but I've mainly used teflon devices for
cooking, so I wanted to see what other people thought.

All these "audiophooles" keep going on about OFC etc.
Then I try to imagine (badly) what the hell is going on at the
molecular level inside a decoupling electrolytic. It must surely
outweigh FR4/Teflon problems

Gullliby yours



martin

 

[[email protected]]

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.

But do your circuits vibrate the room and all it's contents?

Yes, a lot of audiophile stuff is bunk, but microphonics and vibration
in fairly rigid materials are not exactly mysterious concepts.

 

[Fred Bartoli]

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?

 

[John Perry]

John Larkin wrote:




But do your circuits vibrate the room and all it's contents?

Yes, a lot of audiophile stuff is bunk, but microphonics and vibration
in fairly rigid materials are not exactly mysterious concepts.

But there has to be a specific responder to the vibration. Audiophooles
(LOVE that term! Who came up with it?) who can't do without their tubes
have to think about vibration because that's one of the main
deficiencies of tubes, along with their built-in parameter corrupter,
the filament.

Some cables have a piezoelectric response to vibration, and of course,
anything mechanical has to consider it, but FR-4???

John Perry

 

[nospam]

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?

SRBP is not as hard as FR4 either. Gotta wonder why audiophiles always
choose the most expensive solution to their perceived problems.

 

[[email protected]]

But there has to be a specific responder to the vibration. Audiophooles
(LOVE that term! Who came up with it?) who can't do without their tubes
have to think about vibration because that's one of the main
deficiencies of tubes, along with their built-in parameter corrupter,
the filament.

Some cables have a piezoelectric response to vibration, and of course,
anything mechanical has to consider it, but FR-4???

Well it seems like it would be easy to test... design the same pre-amp
and fabricate it on FR-4 and teflon microwave material. Set each up
with no input (or perhaps a clean source) near a speaker driven with a
slow sweep and measure coupling to the circuit. If there is an effect,
one would expect to see responses corresponding to mechanical
resonances of the PCB and/or certain components, with the fiberglass
board having a larger response.

Have to be carefull to mount components identically.

 

[martin griffith]

snip
Audiophooles
(LOVE that term! Who came up with it?

Think it was me, or possibly John Woodgate


martin

 

[martin griffith]

Think it was me, or possibly John Woodgate


martin

nope, was not me, found references going back to 2001


martin

 

[nospam]

Well it seems like it would be easy to test... design the same pre-amp
and fabricate it on FR-4 and teflon microwave material. Set each up
with no input (or perhaps a clean source) near a speaker driven with a
slow sweep and measure coupling to the circuit.

You don't test audio equipment like this. You need meters for....

Musicality
Etch
Resolution
Glare
Detail
Tightness
Speed
Depth
Size
Location
Pace
Brightness
Balance
Flavour
Bloat
Cleanliness
Extension
Energy
Warmth
Fullness
Weight
Smoothness
Liveliness
Sparkle
Power
Sweetness
Correctness
Naturalness

and that is just for cables.

 

[mw]

"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

 

[Joerg]

Hello John,

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.

Gold plating all top and bottom layer traces might help sell it anyways.
Glitz is important and the more expensive it is, the more hip it is
going to be.

Might add a vibration compensation super duper gold cap, too. Must look
very impressive but doesn't need to be connected to anything.

Regards, Joerg

 

[John Larkin]

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

 

[John Larkin]

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

 

[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.

I agree that crystals are prone to vibration problems.

I am surprised that springs solved your problem. Many times a spring
will merely change the frequency of the mechanical resonance. It's
better to eliminate the resonance entirely by more firm mounting, or if
that is impractical, use a vibration dampening material. Sometimes just
moving the component to a place on the pcb that is less disturbed by
vibration (close to a mounting screw) is good enough. Then you'd run
sweeps on an electrodymaic shaker to prove the fix.

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

Vibration induced piezolectric noise from capacitors is a well-known
problem. 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 think it all depends on how "quiet" is "quiet" for your application.
Some people can accept hissy, buzzy audio, and others know that things
can be made quieter.

mw

 

[John Larkin]

I agree that crystals are prone to vibration problems.

I am surprised that springs solved your problem. Many times a spring
will merely change the frequency of the mechanical resonance. It's
better to eliminate the resonance entirely by more firm mounting, or if
that is impractical, use a vibration dampening material. Sometimes just
moving the component to a place on the pcb that is less disturbed by
vibration (close to a mounting screw) is good enough. Then you'd run
sweeps on an electrodymaic shaker to prove the fix.

The oscillator was sensitive to high-frequency vibration, and the
resonant frequency of the spring-mass system was way below the
sensitive range, so the sharp shocks from connector mating couldn't
penetrate to the crystal. The crystal *was* firmly mounted to the
board, which was exactly the problem, and relocating it would have
trashed the entire design. The springs work great.

Vibration induced piezolectric noise from capacitors is a well-known
problem. 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 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.

I think it all depends on how "quiet" is "quiet" for your application.

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.

Some people can accept hissy, buzzy audio, and others know that things
can be made quieter.

How will a microphonic cap make hissy, buzzy audio?

John

 

[Fred Bloggs]

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.

That story is some kind of deceitful ruse, no such thing occurred...