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Old 30th October 2006, 03:17 PM   #1
Tenson is offline Tenson  United Kingdom
diyAudio Member
Join Date: Feb 2006
Location: Kent
Default DC blocking caps for line level


I need to block 2.5V DC on a line level audio signal.

I have been trying a few caps and found that something like a 0.68uF polyprop cap introduced some levels of IMD and HD. I switched to a 0.1uF paper in oil and the HD reduced but the IMD increased. I then tried a 2.2uF PIO cap and the IMD also reduced.

So a bigger cap gives less IMD and paper in oil had less HD than a polyprop Okay, so I tried a 22uF and an 11uF cheap electrolytic. The IMD reduced again but was about the same for both the 11uF and the 22uF (I have seen 10uF as a standard value for this before).

So my question is simply, what do you recommend as a good quality DC blocking cap? Is there any point going much above 10uF? Are there any drawbacks to using a very big value? and, what is the best type of cap?

Thanks to anyone who can enlighten me lol!

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Old 30th October 2006, 03:51 PM   #2
Tenson is offline Tenson  United Kingdom
diyAudio Member
Join Date: Feb 2006
Location: Kent
I found this article which is interesting. It shows why the PIO had less distortion than the polyprop I guess.


So still, I wonder if there is any disadvantage to going above about 10uF?
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Old 30th October 2006, 04:35 PM   #3
Tenson is offline Tenson  United Kingdom
diyAudio Member
Join Date: Feb 2006
Location: Kent
Okay I think the HD was a measurement glitch so the only thing was IMD from the value of the cap.
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