DC voltage across a cap vs. Signal transfer - Page 3 - diyAudio
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Old 9th December 2012, 06:59 PM   #21
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Quote:
Originally Posted by DF96 View Post
I'm not sure what was the point of the link in post 14. It is well known that high-k ceramics are very non-linear dielectrics, which is why they are only used where this does not matter. The writer of that piece from the cap manufacturer seemed to be labouring something obvious; perhaps he was a junior engineer who had only just realised it himself? High-k ceramics are never used for coupling in serious audio systems.
The point was to share findings and hope for more discussion. Not all here are engineers whose primary job is electronics. Me amongst them. What is obvious and well known to you may not be even clear to others.
Whoever, junior or senior, wrote the piece had more knowledge than I did. I found it and I share with diyers. It is up to you if you use it.
DF96, you seem to have deep knowledge, so share it with me / us.
Back to topic, I can see clearly how electrolytic or film caps respond to signal in function of DC voltage across it. It proves you were right and that is the point no. 2

Last edited by yagoolar; 9th December 2012 at 07:02 PM.
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Old 9th December 2012, 07:22 PM   #22
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I have (for too long time ) planned to measure 3rd harmonics from caps using a signal generator (1kHz) a twin-T filter tuned to 1KHz and a RMS V-meter.
You simply measure the signal through the filter without a cap and calibrate the V-meter for zero reading. Add a cap and you should see harmonics give a reading.
It could be a piece of cake to attach a voltage supply across the cap and see if that adds harmonics.
Have to add this to my "must-do list".
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Old 9th December 2012, 09:20 PM   #23
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Distortion from all except the very worst caps is quite small so you will have difficulty in measuring it. The twin-T filter, assuming it will be boostrapped, may produce more distortion than many capacitors. And the filter will include caps itself.

Think of it like this: how would you measure inaccuracies in a ruler when all your measuring equipment is based on rulers?
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Old 10th December 2012, 04:59 AM   #24
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Well, I cvalibrate my equipment with all parts EXCLUDING the caps connected. Whatever I add to my setup in the next step will be measured.
I have a RMS-meter capable of measuring down to at least -120dB. IF a cap is bad enough it is detectable.- This setup is/was used when measuring so called Klirr, 3rd harmonic distortion.
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