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mojopin 22nd November 2007 01:50 AM

Basic question about capacitors
 
Hi, I bought some old speakers that have a simple crossover inside. Just one cap and an inductor. Anyhow, I would like to replace the capacitor. The writing on it says:

WC plus/minus 5%
200V
5.0 MFD

I can't find a capacitor with those specs. Does the 200V matter? Can someone recommend something?

Also, do I need to replace the inductor or do those things last? These speakers are probably from the late 70's.

Thanks a bunch!
mojo

Geek 22nd November 2007 07:04 AM

Hi,

Assuming 8 ohms, 200V is 5,000 watts. That's an unrealistic power level for any tweeter, so I'd say that's not important. It's possible the manufacturer found 200V caps cheaper than 50V or 100V ones at the time. It happens.

5.0uF is close enough to 4.7uF to use that. If you want precision, use two 10uF caps in series.

Also, you may want to avoid electrolytics in crossovers. Sure they are cheap, but.... :xeye: 5% indicates a polyester or polypropylene anyway.

Cheers!

Ouroboros 22nd November 2007 07:44 AM

A 5% 200v cap will not be an electrolytic as 'geek' points out. A polyester cap is unlikely to have degraded in this time, so if there is no physical damage to it, I wonder why you want to replace it?

Likewise the inductor should be ok, although it may not be of the highest quality. I'd possibly tidy the wiring up a bit and make sure the crossover board is mounted securely in the speaker, and leave the components as they are.

mojopin 22nd November 2007 04:37 PM

Thanks for the replies.

The reason I wanted to replace it was to hear if it made an improvement. There doesn't appear to be any damage. The speakers do ring and distort at some frequencies but that is probably a problem with the drivers themselves. The reason this is high wattage is because this speaker is a line array. That crossover is powering 9 four inch mids and 8 two inch tweeters.

I am curious, would I hear a bad capacitor or one that is getting old? Or would it just stop working?

Thanks!

AndrewT 22nd November 2007 04:51 PM

If the speaker designer has done his job well, he will have "voiced" them to sound good with the installed crossover components.
If you change either of these components you will change the characteristics of the filters and how they interact with the variable impedance that the drivers form with them.

If the designer has banged together any old rubbish, then you may be able to improve them. But you will need a big stock of apparently similar components to swap between and an infinite amount of patience to chance upon the combination that sounds as nice as these speakers are capable of sounding.

If they are already distorting on clean signal then they are probably damaged. You cannot get damaged drivers back to sounding good by swapping crossover components.


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