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Old 1st February 2014, 06:27 PM   #11
PMA is offline PMA  Europe
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I am not saying that everything is reflected in harmonic distortion test. I have never said that. Harmonic distortion is provided to show there is now fatal flaw in the setup.

Anyway, I would appreciate if YOU, as a professional, suggest a dynamic test. Other than oscilloscope and step response, it will be of course done, and it will show no difference. What are you suggesting, a Hirata test?

Back to the earth - we shall have some low frequency roll off. Like -2.25dB/20Hz and -0.4dB/50Hz. This will be same for both capacitors used. In fact, this measurement was done with Mundorf in left channel and Roderstein in right channel. But, it disqualifies a test with wire, IMO.
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File Type: png captest_freq_lf.PNG (9.9 KB, 188 views)
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Last edited by PMA; 1st February 2014 at 06:31 PM.
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Old 1st February 2014, 06:28 PM   #12
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Quote:
Originally Posted by kouiky View Post
If any change is found to be under -70dB, it is unquestionably inaudible.
You would be surprised that this is completely wrong idea.
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Old 2nd February 2014, 12:12 AM   #13
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What nominal as well as measured value are the tested capacitors?

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Old 2nd February 2014, 04:51 AM   #14
Johno is offline Johno  Australia
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Hi Pavel,
May I suggest an alternative hopefully simpler methodology - that is to measure the capacitors.

Real world caps of course have an ideal capacitor with series and parallel lumped resistance and lumped inductance. This implies that the capacitor under test is a network with both series and parallel resonances that are relatively easy to identify with a frequency sweep and an accurate voltmeter or oscilloscope. Roederstein had this info on their data sheets by the way and those resonances do impinge, to an extent, on the audio spectrum. (by the way I personally suspect that manufacturers who do not publish are trying to hide low quality "stuff" with marketing spin)

Anyway, by understanding a capacitor and its parasitic elements the compromises should then be clear to an experienced technician or engineer and so aid the identification of the best fit component for your application.

My problem is that distortion measurements near the noise floor can be tenuous and inconclusive.
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Old 2nd February 2014, 05:02 AM   #15
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Hi John,

I know exactly what you mean, I can give it a try.

Thanks,
Pavel
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Old 2nd February 2014, 05:06 AM   #16
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Quote:
Originally Posted by TNT View Post
What nominal as well as measured value are the tested capacitors?

//
Please check image in the first post, for nominal value.
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Old 2nd February 2014, 06:01 AM   #17
RNMarsh is offline RNMarsh  United States
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I would use an RC network that allows for voltage drop across the cap... that is when the distortion will be highest. Maybe standardize at a certain voltage (1v ?) across the cap.

As a coupling cap app, the distortion will be the lowest. In a speaker XO, the distortion will be higher as there will be freq-voltage across the cap. (or any EQ/filter situation -- RIAA, etc).

Thx-RNMarsh
PS - what is the hardware and software you will be using?
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Old 2nd February 2014, 06:49 AM   #18
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Of course. The possible distortion may appear only in case that the capacitor is heavily loaded, as in case of speaker crossover.

I have tried swept sine and step response, and it both revealed nothing. For the step response, generator with output impedance 50 ohm - capacitor - 50 ohm terminating resistor is clean and is an exact copy of the generator leading edge, 15.2 ns. All possible errors are masked by 8-bit DSO accuracy. At least, no visible resonances <20MHz.
Attached Images
File Type: png system_response.PNG (21.5 KB, 161 views)
File Type: png step_roederstein2.PNG (21.3 KB, 157 views)
File Type: png step_mundorf3.PNG (21.3 KB, 153 views)
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Old 2nd February 2014, 07:42 AM   #19
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Measurement of distortion across the cap, with cap driven trough 1k resistor, has shown nothing. Only some method residuals, anyway THD below 0.0004%. And, such situation is completely unrealistic, when the cap is used as a coupling cap. So, no other thing than good ears may help!
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File Type: png Roederstein THD.PNG (68.5 KB, 155 views)
File Type: png Mundorf_THD.PNG (68.8 KB, 31 views)
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Old 2nd February 2014, 08:23 AM   #20
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Thanks, whats the measured capacitance? 8 bit DSO will hardly suffice in these tests!?

Do you have a plan on if/how to vary signal level, source and sink impedance (RLC) as seen from the DUT?

How do you isolate the (varied) DUT environment but still keep the environment constant for the measurement system?

This opens up for som nasty amount of combos per DUT. What will your strategy be?

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