RTA 11T high freq issue

giles302

Hi all. First of all, I love vintage Polks! I've got a pair of Monitor 11s, 5Jrs, SDA 1Cs, and just picked up a pair of RTA 11Ts locally.

I'm having a problem w/ one of the 11Ts, and need some advice. One of the speakers sounds weak or muffled in the high frequencies. The tweeter is working, but doesn't have the same output as the tweeter in the other cabinet. I swapped tweeters between the speakers, and the problem stays w/ the cabinet (not a tweeter problem). I swapped the speakers L & R with the amp, and the problem follows the cabinet (not an amp problem).

I tried to bypass the polyswitch in the crossover, but that didn't help either.

Could I have a bad series cap in the crossover? Any ideas what to look at next?

Thanks for any help you can provide!

ben62670

Welcome to Club Polk. It sounds like you have a bad tweeter, or a bad cap. Try swapping tweeters from one channel to the other to see if it is the tweeter, or the XO.

Ben

treitz3

Ben, it looks like he has done that already. Sounds like it's something in line from the speaker post to the tweeter.

Oh, 302 welcome to the forum.

Face

Can you solder?
http://www.polkaudio.com/forums/attachment.php?attachmentid=18707&d=1155781929

ben62670

treitz3 wrote: »

Ben, it looks like he has done that already. Sounds like it's something in line from the speaker post to the tweeter.

Oh, 302 welcome to the forum.

OK. I'm tired:o

treitz3

Happens to the best of us Ben. Tis'all good.

dcmeigs

I'd swap crossovers to see if the problem moves with the crossover, but yes is does sound like a cap.

Have you found the crossover schematic in the first thread of the troubleshooting section?

It's a simple fix if you can solder. Do a search for crossover mods in the vintage section and you will learn about sources for caps and your many options.

giles302

Thanks for all the quick replies! My next step is to swap crossovers. I was holding off on doing that until I had a chance to hear from the experts on alternate ideas. :-)

If I can isolate the problem to the crossover, I should be able to make a fix. I've done lots of soldering, so that shouldn't be a problem once I get the parts.

Giles

dcmeigs

If I remember correctly, that crossover has a cap in series with an RC (cap and resistor in parallel). Check that resistor too. You can do that with the resistor in place by leaving your leads across the resistor until the cap charges up (and the meter stops moving). A failing resistor would give you the signal loss you describe.

giles302

I checked, and both resistors on both crossovers measure the same.

It looks like the RTA 11T & Monitor 10 use identical crossovers. Is there any reason I can't just swap in a Monitor 10 crossover I can find on ebay?

Link: Monitor 10 sch

Link: RTA 11T sch

Face

Not all monitor 10 crossovers are the same due to the different tweeters used over the years.

giles302

But if I can get a set of Monitor 10 crossovers that have the same components as my 11T, they should be a drop in replacement, right?

Face wrote: »

Not all monitor 10 crossovers are the same due to the different tweeters used over the years.

giles302

Just wanted to close this off. I purchased a set of Monitor 10 crossovers, and they dropped right in (even the wiring harness lengths were the same as my 11Ts). I verified the component values, and they were identical between the 11T & 10B crossovers. Both speakers now sound great. Thanks all for your assistance!

dcmeigs

Congratulations. Now you can visit the soniccraft website and buy some new Gen I Sonicaps and 5 watt mills resistors for those old crossovers. Once finished, you can swap them in for even better sound.