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ngccglp
12-12-2006, 01:31 AM
Hi,

I noticed in most of JBL XO, they connect capacitors, usually a larger value say 2 uF with another 0.01 uF in parallel. May I know is this the preferred way instead say just using a 2.2 uF? What is the purpose of the parallel circuit?

Thanks

johnaec
12-12-2006, 07:45 AM
That's called "bypassing" the caps, but I'll let others more technically literate explain exactly what it does and why it's done.

John

4313B
12-12-2006, 07:58 AM
"It's a trick... get an axe..." - Ash

They aren't required for anything. It was all a marketing ruse.

Titanium Dome
12-12-2006, 08:27 AM
http://www.audioheritage.org/vbulletin/showthread.php?t=3555

Earl K
12-12-2006, 08:27 AM
Hi ngccglp,

- Read this thread (http://audioheritage.csdco.com/vbulletin/showthread.php?t=3555) for a pretty decent backgrounding on the subject ( or subjects ) .
- I've found this "JBL" info is the type that "one can take to the bank" and is especially valuable to the DIYer .

- I'm an active user of this approach ( bypassing "no-name" caps of all sorts ) .
- As stated in the linked-to thread / film & foil polypropylene "bypass caps" will add extra defination ( only you can decide if you actually need it ) while a bit of polystyrene will add a touch of "spaciousness" in the UHF areas.
- JBL has their own established ratios for the sizes to be used. They are; .01 uF for the Polypropylene type "bypass" and .005 uF for the Polystyrene cap ( when both are used with a base Mylar capacitor ).
- I happen to use different sizes and different ratios with my bypass caps. This may be because I'm using metallized polypropylene caps as my basic cap type. As well, I figure that I'm after a more "diffuse" top-end compared to some others ( ie ; I happen to really like the "effect" of adding about .1 uF of lightly dc-biased polystyrene bypass into the mix ) . "Lightly" meaning about 2 volts DC .


- Obviously, I also DC-Bias most caps ( though I'll exclude the oil soaked MPP types, ie; those metalized polypropylene "motor-run" types which don't seem to benefit much at all from the bias treatment ).

- Now if ones' ears aren't up to the challenge of hearing the benefits or if ones' playback system can't pass along the extra resolution that comes by employing either of these two topologies / then / oh well / it'll be money mis-spent .

:)