Rebuilding Monitor 5 Crossover - Necessary?

[uchuujin]

Hi All,

A few months I order parts to rebuilt my Monitor 5's (bought back in the early 80's) after finding that one of the 6502 drivers had frozen. I ordered two new 6502's and two RD0194 tweeters to replace the original SL2000's. As I live overseas and the stuff was all delivered to my U.S. address, and it was a while until I managed to pick them up on my last family visit.

Stangely, after dropping in the new components, I find that one of the new 6502's has bad distortion, even at low volume levels. I swapped it over to the other speaker to see if it was really the driver or perhaps the crossover. I got the same results, so I concluded that the problem really is the new driver. Since I still had one good old 6502, I put that back in and it works fine.

However, one of the new RD0194 tweeters also does not work. I performed the same swap experiment, and the results this time were the opposite. Both new RD0194 tweeters work in one box but not in the other. So in this case, my suspicion is that the crossover in that box is bad.

I remember seeing some plans somewhere for rebuilding the crossovers, but I cannot seem to locate them. Can somebody give me a pointer? Also, any other advice on what I'm experiencing is welcome!

[heiney9]

The x-over is an easy thing to do and I would certainly do it based on your situation. It just so happens I redid my Monitor 5B x-overs and eventually added the RD0's

Here's the link to my project. If you have any questions feel free to PM me, or ask here.

http://www.polkaudio.com/forums/showthread.php?t=51420&highlight=5b%2A

H9

[heiney9]

Do your M5's have an external fuse? If not, then they have an internal polyswitch (which you can see in one of my photos)? Those should be replaced while you have the x-over out. If you ask nicely Polk will send a new pair of polyswitches to you for free.

The polyswitches wear out over time and if they are stuck open sometimes that's the source of the tweeter not functioning.

For cost of $50 in parts and a little of your time you'll have a great performing speaker that you will no longer have to worry about if the x-over has been abused.

H9

[dcmeigs]

I think you will find that H9 is correct. Unless you have fuses, you might want to pull the crossover on the bad tweeter and jump the polyswitch and see if you are good to go until you get around to rebuilding the crossovers.

You have the option to leave the polyswitches out altogether. They are there to protect your tweeters from you (and perhaps to protect from Polk from warranty claims due to yahoos abusing their new speakers during the warranty period). If you can be trusted not to kill your tweeters, I think your fives will sound better without them.

When I did my crossovers, the poly switches were showing two point something ohms on one speaker and one point something on the other. Too much resistance and hardly well balanced. My crossovers are now protection free. My tweets are still alive. Life is good.