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Old 15th July 2012, 06:10 AM   #24521
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Old 15th July 2012, 06:48 AM   #24522
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A capacitor operates only on AC. The author of the capacitor article somehow doesn't seem to understand this. He says:

Quote:
The purpose of bypass caps is to store energy that ICs need on a short term basis, swamp PCB track inductance to ensure that opamps don't oscillate, and to ensure that digital circuits don't generate supply line glitches that produce erroneous data. There is absolutely no 'sound' associated with DC supply rails.
Of course there is no sound associated with DC, but the reference to DC is inappropriate here and simply begs the question. A capacitor is intended as a means of rendering that DC rail pure DC by shunting AC to ground. To the extent the capacitor fails in that function will AC be present on that DC rail.

How does a capacitor fail to shunt AC to ground? When it doesn't operate as an ideal capacitor---such as when its DA/Dk creates distortion as seen in the diagram I posted from Bateman's article.

Power supply capacitors and their shunts are theoretically in series with signal amplifying devices for this reason. I see no proper basis to claim that use of a better bypass capacitor is "sheer lunacy," in the author's words. I see badly thought theory.

Your language was similarly this:

Quote:
Talk about bait and switch a bypass capacitor sees no AC signal (it's there to eliminate it). This is a classic mis-use of Bateman's results. Would anyone use X7R's to make an RIAA, please.
Please justify your statement that a capacitor sees no AC signal when its sole job is to pass AC signal.

Last edited by serengetiplains; 15th July 2012 at 06:51 AM.
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Old 15th July 2012, 06:55 AM   #24523
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Quote:
Originally Posted by DF96 View Post
Ceramics are not universally bad.
DF, what do you actually mean by "bad"? Ceramics don't stop operating as ceramics---their DA/DF/Dk ratings don't change---because they're placed here or there. They're not "good" here and "bad" there. They are what they are, or in other words, they are characteristically nonideal for that type of capacitor wherever you put them.
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Old 15th July 2012, 07:47 AM   #24524
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That's how I feel about ceramic caps, as well, serengentiplains.
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Old 15th July 2012, 08:10 AM   #24525
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Quote:
Originally Posted by Bonsai View Post
Having brilliant minds around the table to dissect and analyze any subject you please is likely to bear fruit.

However, I didn't think abrasiveness adds anything.

Where's Thorsten by the way?
Abrasiveness is good as a stage of cyclic development. Dreaming, construction, criticizing. Circle closed, stop criticizing, go back to dreaming. When Walt Disney learned this strategy he become very productive. He taught his staff. He used 3 different rooms for 3 different tasks. Only one of them was meant for criticizing.
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Old 15th July 2012, 09:27 AM   #24526
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Quote:
Originally Posted by serengetiplains View Post
Please justify your statement that a capacitor sees no AC signal when its sole job is to pass AC signal.
That's correct. A (PSU) bypass capacitor sees all the AC ripple, but a coupling capacitor sees almost no AC in case the frequency is far above 1/2*pi*R*C, for the C-R hipass filter.
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Old 15th July 2012, 10:02 AM   #24527
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Quote:
Originally Posted by serengetiplains View Post
A capacitor operates only on AC. The author of the capacitor article somehow doesn't seem to understand this. He says:



Of course there is no sound associated with DC, but the reference to DC is inappropriate here and simply begs the question. A capacitor is intended as a means of rendering that DC rail pure DC by shunting AC to ground. To the extent the capacitor fails in that function will AC be present on that DC rail.

How does a capacitor fail to shunt AC to ground? When it doesn't operate as an ideal capacitor---such as when its DA/Dk creates distortion as seen in the diagram I posted from Bateman's article.

Power supply capacitors and their shunts are theoretically in series with signal amplifying devices for this reason. I see no proper basis to claim that use of a better bypass capacitor is "sheer lunacy," in the author's words. I see badly thought theory.

Your language was similarly this:



Please justify your statement that a capacitor sees no AC signal when its sole job is to pass AC signal.
The capacitor sees little or no AC VOLTAGE (if your supply rails have 3V AC at 1kHz it is a bad design). No voltage no distortion. Also again DA does not make distortion the voltage coefficient of capacitance does. The AC displacement current does NOT have the distortion. If you don't differentiate between AC signal as current vs voltage, any circuit analysis is difficult.

A properly designed supply would use ceramics as RF bypass since the current loop and parasitic L are minimized. The rails are already stiff at audio frequencies with larger caps of other material.
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Last edited by scott wurcer; 15th July 2012 at 10:11 AM.
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Old 15th July 2012, 10:05 AM   #24528
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Quote:
Originally Posted by PMA View Post
That's correct. A (PSU) bypass capacitor sees all the AC ripple, but a coupling capacitor sees almost no AC in case the frequency is far above 1/2*pi*R*C, for the C-R hipass filter.
PMA, hopefully the ripple is 10's uV at audio in your supplies.
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Old 15th July 2012, 10:09 AM   #24529
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Quote:
Originally Posted by Bonsai View Post
Having brilliant minds around the table to dissect and analyze any subject you please is likely to bear fruit.

However, I didn't think abrasiveness adds anything.

Where's Thorsten by the way?
There used to be a "definition according to Paul" of a design review in memo form (1975 or so). Quite something.
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Old 15th July 2012, 10:29 AM   #24530
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Quote:
Originally Posted by scott wurcer View Post
PMA, hopefully the ripple is 10's uV at audio in your supplies.
Impulse ripple (e.g. during contactor switching in the power distribution net), burst shaped with damped HF oscillations in MHz or tens of MHz, is much higher. Depends on filter and PSU design, and on interconnection of the audio components (instruments) as well.
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