Imagine that...
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DC blocking capacitors audibility.
- Thread starter Sebba
- Start date
Imagine that...
That's nothing.
Imagine a 100 billion dollar company, to conduct flawed listening tests and state something that can so easily be refuted in a forum.
Those idiots!
-300dB idiots!
Very much this:
Even (or perhaps especially) AI can become infected:
Serious Question: How can DAC's have a SOUND SIGNATURE if they measure as transparent? Are that many confused?
It is sufficient proof for me personally, to base engineering decisions on the test results. "good enough", eh? Not in the presence of a positive result giving evidence of 'effect'. You seem under the impression that a reported positive result is unassailable. Science laughs at you. It...
www.audiosciencereview.com
IAtaman
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Which $100B company is that?That's nothing.
Imagine a 100 billion dollar company, to conduct flawed listening tests and state something that can so easily be refuted in a forum.
Those idiots!
-300dB idiots!
Killingbeans
Major Contributor
Texas Instruments? Wasn't it the Chord dude who made the -300dB claims?
IAtaman
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The thread, I have been following. Your logic, on this thread, not as successfully I must admit. First Rob’s accomplishments got mixed into ABX testing, now TI’s market cap is a proof of -300db conspiracy. May I suggest we leave Rob and his bullshit out of this?
solderdude
Grand Contributor
Tube amps all sound heavenly.... yet they are littered with, often even under dimensioned, coupling caps on input and intermediate stages. Go figure.
How much better would these sound if you could get rid of those pesky coupling caps.
How much better would these sound if you could get rid of those pesky coupling caps.
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If we focus on the essentials we have this:
@Sebba has asked on his topic "DC blocking capacitors audibility."(?): "what might be the reason for those differences ?" #1
National Semiconductor has only described effects and no causes with its laboratory report *1) *2). The effects described will be fact, otherwise these hints would never have been published. Even in 2006 it was generally known what effects capacitors (type, value, max. DC voltage) can have at various points in circuits. So even if the LM4702 is no longer produced, we could discuss this not uninteresting topic under the aspect "Problems with LM4702 / PCB layouts?".
I suspect instabilities in a combination of the LM4702 [offset, oscillations, slew rate?] and the PCB layout ["Recommended" in 2006 *1) / Improved layout only for the LM4702 *3)].
*1) LM4702 - Application AN-1490 - 2006
National Semiconductor - Power Amplifier - Mark Brasfield
*2) LM4702 - Application AN-1490 - 2006/2013 - SNAA031A
Texas Instruments - Power Amplifier
(Only changed layout of National Application Note *1) to TI format)
For *1) / *2):
"A DC blocking capacitor on the input of the LM4702 degraded sound quality. ... negative effects of even the best film and foil polystyrene DC blocking input capacitors in the audio signal path was confirmed."
- There is no hint of slew rate [Capacitor CC *3)]
- The input noise capacitor CN is missing
- Look for PCB layout
*3) LM4702 - Application AN-1645 - 2007/2013 - SNAA045A
Texas Instruments - Driving a MOSFET Output Stage
"5
For sonic quality, the design does not use an AC coupling, DC blocking capacitor. The CN capacitor shunts high frequency noise present at the input to ground. The compensation capacitor, CC , sets the slew rate and phase margin to ensure oscillation-free operation. ...
• The values of the gain setting resistors and the input resistors should be equal. RS = RF , RIN = Ri. RS should not be set too low as to cause loading of the source. Setting the resistors to equal values in the associated pairs ensures that the input bias currents will have negligible effect on the input offset voltage.
• Use a silver mica type capacitor for the compensation capacitors, CC capacitors on the COMP pins, placed close to the LM4702.
• The slew rate should be set to the highest possible while maintaining stability through the power and frequency ranges of operation.
• DC blocking input capacitors affect the low frequency response and their value must be chosen accordingly. An additional film capacitor used in parallel may improve the sonic quality. Eliminating the input capacitor will give the best sonic performance.
• The feedback capacitor, Ci , sets the gain at DC to unity and also affects the low frequency response in relation to the value of the Ri resistor. This capacitor's value should be set using the same recommendations given to selecting the input capacitor's value.
• The input noise capacitor, CN , is used to filter high frequency noise that may be present on the input signal. This capacitor may be any type and the value is typically 15pF - 47pF."
*3) LM4702 - Data Sheet - 2005/2013 - SNAS328I
Texas Instruments
REVISION HISTORY: 04/04/13 Changed layout of National Data Sheet to TI format
"(3)
For best noise performance, lower values of resistors are used. A value of 1kΩ is commonly used for Ri and then setting the value of Rf for the desired gain. For the LM4702 the gain should be set no lower than 26dB. Gain settings below 26dB may experience instability."
"(4)
If an input coupling capacitor is used to block DC from the inputs as shown in Figure 1, there will be another high pass filter created with the combination of CIN and RIN . When using a input coupling capacitor RIN is needed to set the DC bias point on the amplifier's input terminal. ..."
"(5)
With large values of RIN oscillations may be observed on the outputs when the inputs are left floating. Decreasing the value of RIN or not letting the inputs float will remove the oscillations. ..."
@Sebba has asked on his topic "DC blocking capacitors audibility."(?): "what might be the reason for those differences ?" #1
National Semiconductor has only described effects and no causes with its laboratory report *1) *2). The effects described will be fact, otherwise these hints would never have been published. Even in 2006 it was generally known what effects capacitors (type, value, max. DC voltage) can have at various points in circuits. So even if the LM4702 is no longer produced, we could discuss this not uninteresting topic under the aspect "Problems with LM4702 / PCB layouts?".
I suspect instabilities in a combination of the LM4702 [offset, oscillations, slew rate?] and the PCB layout ["Recommended" in 2006 *1) / Improved layout only for the LM4702 *3)].
*1) LM4702 - Application AN-1490 - 2006
National Semiconductor - Power Amplifier - Mark Brasfield
*2) LM4702 - Application AN-1490 - 2006/2013 - SNAA031A
Texas Instruments - Power Amplifier
(Only changed layout of National Application Note *1) to TI format)
For *1) / *2):
"A DC blocking capacitor on the input of the LM4702 degraded sound quality. ... negative effects of even the best film and foil polystyrene DC blocking input capacitors in the audio signal path was confirmed."
- There is no hint of slew rate [Capacitor CC *3)]
- The input noise capacitor CN is missing
- Look for PCB layout
*3) LM4702 - Application AN-1645 - 2007/2013 - SNAA045A
Texas Instruments - Driving a MOSFET Output Stage
"5
For sonic quality, the design does not use an AC coupling, DC blocking capacitor. The CN capacitor shunts high frequency noise present at the input to ground. The compensation capacitor, CC , sets the slew rate and phase margin to ensure oscillation-free operation. ...
• The values of the gain setting resistors and the input resistors should be equal. RS = RF , RIN = Ri. RS should not be set too low as to cause loading of the source. Setting the resistors to equal values in the associated pairs ensures that the input bias currents will have negligible effect on the input offset voltage.
• Use a silver mica type capacitor for the compensation capacitors, CC capacitors on the COMP pins, placed close to the LM4702.
• The slew rate should be set to the highest possible while maintaining stability through the power and frequency ranges of operation.
• DC blocking input capacitors affect the low frequency response and their value must be chosen accordingly. An additional film capacitor used in parallel may improve the sonic quality. Eliminating the input capacitor will give the best sonic performance.
• The feedback capacitor, Ci , sets the gain at DC to unity and also affects the low frequency response in relation to the value of the Ri resistor. This capacitor's value should be set using the same recommendations given to selecting the input capacitor's value.
• The input noise capacitor, CN , is used to filter high frequency noise that may be present on the input signal. This capacitor may be any type and the value is typically 15pF - 47pF."
*3) LM4702 - Data Sheet - 2005/2013 - SNAS328I
Texas Instruments
REVISION HISTORY: 04/04/13 Changed layout of National Data Sheet to TI format
"(3)
For best noise performance, lower values of resistors are used. A value of 1kΩ is commonly used for Ri and then setting the value of Rf for the desired gain. For the LM4702 the gain should be set no lower than 26dB. Gain settings below 26dB may experience instability."
"(4)
If an input coupling capacitor is used to block DC from the inputs as shown in Figure 1, there will be another high pass filter created with the combination of CIN and RIN . When using a input coupling capacitor RIN is needed to set the DC bias point on the amplifier's input terminal. ..."
"(5)
With large values of RIN oscillations may be observed on the outputs when the inputs are left floating. Decreasing the value of RIN or not letting the inputs float will remove the oscillations. ..."
MAB
Major Contributor
My surprise isn't that the $300B company (TI) said stated, it's that they present the statement without seeming to have even a clue as to why their part behaves this way.That's nothing.
Imagine a 100 billion dollar company, to conduct flawed listening tests and state something that can so easily be refuted in a forum.
Those idiots!
-300dB idiots!
I don't know, perhaps they do know, but are not inclined to say so. They just put the advice there.My surprise isn't that the $300B company (TI) said stated, it's that they present the statement without seeming to have even a clue as to why their part behaves this way.
But ti, knows how to conduct controlled listening test, to question them on that is rather daft.
The fact remains that on this particular case (isolated perhaps) the advice is valid.
To deduct that ti is claiming any DC blocking cap, in every scenario has sound quality issues is rather short sighted.
Also to claim they want to speak the lingo to appeal to audiophools, in order to sell a few hundred more opamps is equally . . . .
If you think about it, they are admitting a short coming of their chip.
MAB
Major Contributor
Maybe TI put a large DC bias to show that a blocking cap was needed.
Maybe... Who knows? I really can't tell. Which is why this thread is 6 pages long, no hope to answer even a simple question.
fpitas
Master Contributor
A dirty secret is that those papers are often produced by the interns that are available. We have questioned (and they were subsequently corrected) several app notes from TI, Analog Devices etc.
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Not to date myself*
-- but I am reminded of Robert Pirsig's diatribe regarding the poor quality of instruction manuals that pops up in Zen and the Art of Motorcycle Maintenance._________________
* Actually, it gets even worse! I read Zen and the Art of Motorcycle Maintenance because it was a required text in... Molecular & Cellular Biology Lab 2 at JHU way back when. The professor responsible for that course was a piece of work in the worst sense(s) of that term. He went on to do hard time in prison for a variety of unpleasant things.
Oh, and a couple of years later, as a grad student, I was a T/A in that course (oh, Lord, now that I think about it, I was the "head" T/A that year - a suppressed memory, I guess). A couple of years earlier, my (now) wife had also been a T/A in that same course. Not my T/A, though (lest anybody think there was any funny business going on).
Yeah... fun times.
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fpitas
Master Contributor
In the interns' defense, they come out of school and are handed something like a state-of-the-art 14 bit ADC clocking at 5GHz. I can imagine how they feel...Not to date myself*
_________________
* Actually, it gets even worse! I read Zen and the Art of Motorcycle Maintenance because it was a required text in... Molecular & Cellular Biology Lab 2 at JHU way back when. The professor responsible for that course was a piece of work in the worst sense(s) of that term. He went on to do hard time in prison for a variety of unpleasant things.
Oh, and a couple of years later, as a grad student, I was a T/A in that course (oh, Lord, now that I think about it, I was the "head T/A that year - a suppressed memory, I guess). A couple of years earlier, my (now) wife had also been a T/A in that same course. Not my T/A, though (lest anything think there was any funny business going on).
Yeah... fun times.
MAB
Major Contributor
It's no different at the very large company I work at. App notes with paragraphs of obsolete text reused over the ages, often out of context.
A rather important and relevant example involving a capacitor that will have an impact on sound, JBL can't even be bothered to get the filter capacitor value correct in the documented schematic of their flagship studio monitor in multiple documents. And their technical support staff repeats the fallacy, even when presented with a photo of their own crossover. I guarantee that a 33uF vs. a 3.3uF filter cap will have a dramatic and bad effect on the tweeter. So, I put zero stock in TI's app note here, and I don't even care if TI was hallucinating or if they actually heard a diff.
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Taken from a PDF of Zen and the Art of Motorcycle Maintenance that I - ahem - found in some obscure corner of the interwebz.
fpitas
Master Contributor
It is often like that. The best people are busy with complicated things. So, that one doofus guy gets the job...Taken from a PDF of Zen and the Art of Motorcycle Maintenance that I - ahem - found in some obscure corner of the interwebz.
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