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Old 17th March 2013, 01:50 PM   #9511
Salas is offline Salas  Greece
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The value though is serving a sub bass roll off and it should stay away of major play. 47nF as given or 100nF max for test.
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Old 17th March 2013, 01:53 PM   #9512
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by buzzforb View Post
...............
Caps have a sound. I dare not even speculate as to why this is, but they do.
Buzz,
in what situations have you found this to be true?
When
Quote:
the capacitor have significant audio signal across it?
or ..... the capacitor have insignificant audio signal across it?
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Old 17th March 2013, 01:54 PM   #9513
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Quote:
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The value though is serving a sub bass roll off and it should stay away of major play. 47nF as given or 100nF max for test.
That is what I assumed.
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Old 17th March 2013, 02:13 PM   #9514
AndrewT is offline AndrewT  Scotland
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Originally Posted by buzzforb View Post
............Both of the coupling caps do pass the signal, .............. Significant is a tough question. It is significant enough that the value is important for the passage of the signal across the full audio band. ...........
significant or not?
If you have a 1uF coupling capacitor with a perfect dielectric and zero parasitics (impossible but a vacuum dielectric may get closer than plastic films)
feeding a 100k input stage with audio frequencies over the full range of 20Hz to 20kHz, then the impedance seen by a 20Hz signal is 100k + [1/2/Pi/F/C] = 100k + 7958ohms.
The 7958ohms is just under 8% of the total impedance seen by the signal. That could possibly be defined as insignificant.

If the input Zin of the stage were instead 10k, then the total impedance seen by the signal is now 10k + 7958ohms.
I and most others would define that as a significant impedance due to the same 1uF capacitor.

If you inserted a pair of 22uF back to back bipolars with an effective capacitance of 11uF along with the 10k Zin, you would now have 10k + 723ohms. I think that would just about become insignificant.
One of Whitlock's papers suggests a single 220uF bipolar for a coupling cap. I think he has the same ideas in mind.
When the signal across the capacitor is insignificant, the capacitor can only contribute insignificant added distortions to the signal. In this insignificant situation the type of capacitor also becomes insignificant.
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Last edited by AndrewT; 17th March 2013 at 02:29 PM.
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Old 17th March 2013, 02:27 PM   #9515
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Interesting Andrew. I will give it a try, as I am open minded about the subject.
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Old 17th March 2013, 03:14 PM   #9516
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by AndrewT View Post
Dielectric will have an audible effect even when cap values are very accurately matched. It may take extreme differences in dielectric parameters to show the audible effect for some of the caps in the RIAA, but do not discount the notion that some caps may show an effect for what might appear to be quite small differences in cap parameters.

But this can ONLY be validated if the differences in cap values are very rigorously eliminated for the whole range of operating temperatures inside the working RIAA stage.
Totally agree, but I was warning against the urge to replace caps with "better" ones without taking care to use the EXACT same values, because that can lead the experimenter to believe some cap types might sound "better" than others.

Value is critical is this case.... off course, if you are sure about the correct values then you can choose "better" caps.... allready mensioned my choice of polystyrenes on tin foil

Now I am using NOS military teflons (inexpensive from russia) and found they are quite good once we use the correct values.

Now regarding interstage coupling caps, the value is not so critical and these have an imediate effect on sound.

Changing from foil polyprops to something more elaborate as foil on teflon gives tremendous imediate benefits.
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Old 17th March 2013, 03:20 PM   #9517
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by AndrewT View Post

One of Whitlock's papers suggests a single 220uF bipolar for a coupling cap. I think he has the same ideas in mind.
When the signal across the capacitor is insignificant, the capacitor can only contribute insignificant added distortions to the signal. In this insignificant situation the type of capacitor also becomes insignificant.
Interesting theory but I found that normally small value film capssomehow sound faster and cleaner than big value EL.

Even when comparing between films only, smaller values sound faster than higher values.
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Old 17th March 2013, 03:28 PM   #9518
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Maybe because the smaller values produce less bass because they form a high pass filter ?
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Old 17th March 2013, 03:29 PM   #9519
AndrewT is offline AndrewT  Scotland
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Consider what capacitor parameter could be causing the "change" in sound quality.
Could it be esr, or esl, or da, or some other.

Simply guessing at what to try next will not get to eliminating the distortion that is being heard. Especially if the distortion cannot be eliminated entirely and can only be attenuated until it is sufficiently below the noise floor that it becomes impossible for any human to detect.
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Old 18th March 2013, 02:18 AM   #9520
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WOW !
Busy afternoon over here guys...
...just caught up.

Si.
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