From an audio forum... FR4 question

[Ted Edwards]

made it wobble like one of those gooney-head dolls you see in the
backs of cars.

Ummmmmm, I thought those were in the left front seat.

Ted

 

[Pooh Bear]

You're kidding me, right?

John

Non-linearity *inside the feedback loop path* is amplified by the feedback factor.

Negative feedback requires the components to be linear to operate as advertised.

Think about it.

Graham

 

[Pooh Bear]

The bipolar ones are often the worst way to go. Using two polar ones and
applying a large pre-bias works better.

When required, I tend to use two polar types 'back to back' and apply a polarising
voltage via a high resistance to the centre point.

For the most part a single polar type works well though provided that the A.C.
voltage across it doesn't exceed that ~ 100mV level.

Graham

 

[John Larkin]

Especially line cords.

Ted

Good ones. I've added them to my list:

5N, 6N, 7N (as in 99.99999 pure copper)
acceleration
agressive
air
articulation
authority
bass transient response
blackness
bloom
bright
burnin (cables)
clarity
color
confused
congested
continuousness
crisp
delineation of inner detail
dynamics
edge
effortlessness
etched
extension
fast bass
free-flowing ease
glare
grainy
granularity
hangover
hard
harmonic completeness
hashy
holographic
honesty
image specificity
impact
jump
layering
liquid
liquidity
liveliness
lush
macrodynamics
microdynamics
macro-to-micro intensity
musicality
openness
pace
quantum purifier
reference
refinement
relaxed
roundness
reveal
single-crystal copper
slam
slow bass
smear
soundstaging
space
sparkle effect
spatial resolution
speed
stunning (everything is stunning)
thin
tight
tight (bass)
timbre
tipped-up
transparency
truth
unfussiness
wire direction



John

 

[John Larkin]

Non-linearity *inside the feedback loop path* is amplified by the feedback factor.

If you mean the actual feedback path, not the forward path, sure. But
the feedback path is almost always passive.

John

 

[Pooh Bear]

If you mean the actual feedback path, not the forward path, sure. But
the feedback path is almost always passive.

Sure. But may contain non-linear components such as med or hi-K dielectric caps.

Therefore their use inside the feedback path exageerates their non-linearity and should
be avoided.

I've even experienced non-linear resistors too btw. Just once. A batch of 'bad' 27ks.

Graham

 

[Ken Smith]

The bipolar ones are often the worst way to go. Using two polar ones and
applying a large pre-bias works better.

When required, I tend to use two polar types 'back to back' and apply a
polarising
voltage via a high resistance to the centre point.
Yes.

For the most part a single polar type works well though provided that the A.C.
voltage across it doesn't exceed that ~ 100mV level.[/QUOTE]

I assume that 100mV is under 10% of the DC component and well under the
rating.

I'd worry about a capacitor rated for 5.6V with 100mV on it.

 

[Ken Smith]

I don't think it's Vectron especially; all XOs are shock/acceleration
sensitive to various extents. SC-cuts are supposed to be better, at
roughly 3-5x the price.

They are, they are and they are $300 (about).

Almost every oscillator will change frequency when you turn the PCB over.

I believe all SC cut crystals are used in ovens.

 

[John Larkin]

Sure. But may contain non-linear components such as med or hi-K dielectric caps.

Therefore their use inside the feedback path exageerates their non-linearity and should
be avoided.

I've even experienced non-linear resistors too btw. Just once. A batch of 'bad' 27ks.

Graham

Well, I guess that thing to do is not to use nonlinear parts if they
cause too much nonlinearity. That's what engineering is all about.
What engineering is *not* about is following stock rules.

The place resistor nonlinearity gets serious is precision high-voltage
stuff, where it's a serious problem.

John

 

[Fred Bartoli]

Sure. But may contain non-linear components such as med or hi-K dielectric caps.

Therefore their use inside the feedback path exageerates their non-linearity and should
be avoided.

No, it doesn't exaggerate their non-linearity.
Non linerity effects simply can't be reduced there, but no they can't be
amplified.

 

[Ken Smith]

No, it doesn't exaggerate their non-linearity.
Non linerity effects simply can't be reduced there, but no they can't be
amplified.

except: If a non-linear part anywhere in the system generates harmonics
near or above the gain crossover point, they can be boosted. If the phase
shift is within 60 degrees of 180, there can be peaking at the harmonic's
frequency.

 

[[email protected]]

On 13 Nov 2005 01:44:11 -0800, [email protected] wrote: [snippage]
Geez, don't tell Fred!

I don't think it's Vectron especially; all XOs are shock/acceleration
sensitive to various extents. SC-cuts are supposed to be better, at
roughly 3-5x the price.

My one wasn't sensitive to acceleration; it appeared to be a
steady-state phenomenon. I could stress (i.e. bend) the board a
little, and the frequency would change, and would've stayed changed had
my loop not pulled it back.

Regards,
Allan

 

[John Larkin]

OMG, are the audiophools going be pissed at you!

The dirty secret is that they all buy their wire from the same few
mills.

John

 

[Ken Smith]

I don't think it's Vectron especially; all XOs are shock/acceleration
sensitive to various extents. SC-cuts are supposed to be better, at
roughly 3-5x the price.

My one wasn't sensitive to acceleration;[/QUOTE]
^
Insert the word "very" as marked and I'll believe you but without it, you
would have a very hard time proving it if it ever happened.

I've never seen a crystal under 0.5PPB/G

it appeared to be a
steady-state phenomenon. I could stress (i.e. bend) the board a
little, and the frequency would change, and would've stayed changed had
my loop not pulled it back.

This sounds like it wasn't actually the crystal that was causing the
shift. Perhaps the capacitors were being stressed and changing values.

 

[[email protected]]

My one wasn't sensitive to acceleration;

^
Insert the word "very" as marked and I'll believe you but without it, you
would have a very hard time proving it if it ever happened.[/QUOTE]

Can I use the word 'particularly' instead?

This sounds like it wasn't actually the crystal that was causing the
shift. Perhaps the capacitors were being stressed and changing values.

Yes, I had also considered that it might be caused by a 1uF MLCC in the
loop filter. (I don't recall the dielectric material, but it was a
physically large part (1206?).)
Alas, this design has been retired, so I won't have a chance to open
the loop and find the real cause of the problem.

Regards,
Allan

 

[Ken Smith]

<[email protected]> wrote:

[...]

^
Insert the word "very" as marked and I'll believe you but without it, you
would have a very hard time proving it if it ever happened.

Can I use the word 'particularly' instead?

That'll work too.

[...]

Yes, I had also considered that it might be caused by a 1uF MLCC in the
loop filter. (I don't recall the dielectric material, but it was a
physically large part (1206?).)

SMD 2520 is a physically large part. Is that the size of the 1uF? If it
was 1uF and 1206, this couldn't have been very long ago and the material
had to be a very high K one.

Alas, this design has been retired, so I won't have a chance to open
the loop and find the real cause of the problem.

Your designs retire early. It must be nice.