RTA 11t Crossover service

[59ctd]

I have a pair of Polk RTA 11t towers that I've owned for nearly 30 years now. I am getting my sound system back into working order with new receiver, etc. I think I heard somewhere that the caps on a 30 year old loudspeaker crossover likely need replacement. How do I know and is there anywhere with a bit more info on what to look at and replace? I am handy and able to take them apart and solder in replacements, etc but I am unsure if this is really something to worry about.

 

[kevintomb]

Almost for sure at that age. And expect a big improvement in clarity, no matter what brand of cap you use!

 

[Benni777]

Yeah agreed on the above from Kevintomb. I would open that bad boy up and get an idea of whats in there and going on, then do a bit of research. I help a buddy of mine repair his XO in a pair of Polks he had, it was fairly easy and made a huge difference. That being said in his case he had blown the XO.

 

[TLS Guy]

I have a pair of Polk RTA 11t towers that I've owned for nearly 30 years now. I am getting my sound system back into working order with new receiver, etc. I think I heard somewhere that the caps on a 30 year old loudspeaker crossover likely need replacement. How do I know and is there anywhere with a bit more info on what to look at and replace? I am handy and able to take them apart and solder in replacements, etc but I am unsure if this is really something to worry about.

If the caps are electrolytic types, then they may well need replacement. If they are not, then they almost certainly don't need replacement. This is a DIY job.
It is one of a number of reasons I never use electrolytic caps in a speaker design, and always good quality non electrolytic designs. Commercial designs usually do it on the cheap and hence the problem.

 

[kevintomb]

There is also an issue with the protective circuit for the tweeter that Polk used back then.

It is the very thin tiny thing on the board, that many find builds up resistance after being tripped many times. Most replace it with a 1/2 ohm resistor, that equals the resistance it adds to the circuit.

Another issue (going from memory...so...) is that Polk used 2 caps for the tweeter circuit on this model, and they are not truly necessary to use two.

There is a simplified slightly modified crossover that works exactly the same, without using 2 caps.

The two 12uf get expensive in each speaker, and can be changed to a much less expensive one cap version.

 

[59ctd]

I have not replaced the crossover caps yet. What is a sign these are bad? I have a 6.1 system with a Yamaha RX-A3030. I've had it working for a few days now and it just sounds muffled and WAY lower sound output. If it is the caps on the main polks then I might need to do the same on the front center and all three rear speakers too. They are not quite as old but they are well more than 20 yrs old now

 

[ryanosaur]

Electrolytic caps will swell or leak. I’ve seen references that say non-polarized electrolytic caps do not, but I cannot confirm this.

 

[Eppie]

I have not replaced the crossover caps yet. What is a sign these are bad? I have a 6.1 system with a Yamaha RX-A3030. I've had it working for a few days now and it just sounds muffled and WAY lower sound output. If it is the caps on the main polks then I might need to do the same on the front center and all three rear speakers too. They are not quite as old but they are well more than 20 yrs old now

Electrolytic caps can go out of spec with age but may not show any visible signs. As above, typical visual sign is swelling on the ends or leakage of internal fluid, but if they look fine they can still be out of spec. Only way to know for certain is with a capacitor tester. Considering the age, you have little to loose with replacing the caps. You don't need to go and spend crazy amounts on Jantzen or Mundorf caps. Audyn or Dayton polypropylene will work fine.

 

[kevintomb]

If they are that old, OR sound muffled or any of the above..time to replace. As Eppie said, any basic cap will work fine!

 

[59ctd]

I appreciate the inputs guys/gals. I finally had the time to take one of the RTA-11t's apart. I think the date code is telling me they were made in 1988 which seems about right to me. I am still unsure what capacitors I should replace. It looks like there is a 12uF and a 34uF electrolytic caps and a lot larger one in the center. I found a lot of pics online for the 11t's and this seems a bit diff with two small ohm 5W resistors - one is under the 12uF cap.

 

[highfigh]

Electrolytic caps will swell or leak. I’ve seen references that say non-polarized electrolytic caps do not, but I cannot confirm this.

They usually won't swell unless they're hit with high voltage or, at least, high WRT their rating but it depends on their construction. Non-polar caps can be damaged but it's almost always over-voltage that causes it (defects would account for the rest).

 

[Verdinut]

Electrolytic caps can go out of spec with age but may not show any visible signs. As above, typical visual sign is swelling on the ends or leakage of internal fluid, but if they look fine they can still be out of spec. Only way to know for certain is with a capacitor tester. Considering the age, you have little to loose with replacing the caps. You don't need to go and spend crazy amounts on Jantzen or Mundorf caps. Audyn or Dayton polypropylene will work fine.

The Solen caps are as good if not better than many other other polypropylene caps on the market. Those are made by a Canadian company with its website as Solen.ca.

Those are also sold by in the US by Parts-Express and Madisound. TLS Guy and I use them when we build passive crossovers.

 

[kevintomb]

I appreciate the inputs guys/gals. I finally had the time to take one of the RTA-11t's apart. I think the date code is telling me they were made in 1988 which seems about right to me. I am still unsure what capacitors I should replace. It looks like there is a 12uF and a 34uF electrolytic caps and a lot larger one in the center. I found a lot of pics online for the 11t's and this seems a bit diff with two small ohm 5W resistors - one is under the 12uF cap.

Just the 12uf caps will make the most bang for the buck, as they are on the tweeter circuit.
The 34 is on the low pass circuit of the woofer to filter highs from the woofer, and its large size is best replaced with a similar electrolytic cap, as anything else is too expensive.

Dayton or audyn caps are fine. Most of the rest are a waste of money.

 

[lovinthehd]

If you've taken the caps out of the crossovers you should be able to test for spec....

 

[Eppie]

The Solen caps are as good if not better than many other other polypropylene caps on the market. Those are made by a Canadian company with its website as Solen.ca.

Those are also sold by in the US by Parts-Express and Madisound. TLS Guy and I used them when we build passive crossovers.

Yeah, I keep forgetting to mention Solen. For that matter, the op doesn't have to use polypropylene. I new set of electrolytics will last another 15 or 20 years. If there is someone to pass those speakers down to then the extra cost of polypropylene might be worth it.

 

[59ctd]

Ok, this is the closest pic I've found online to the crossovers I have in above pics from my 11t's. Credit - https://forum.polkaudio.com/discussion/7190/rta-11t-crossover-upgrade-to-tl-wiring-schematics-are-here/p1

I had been thinking that the 12uF and 34uF electrolytic capss were the ones to replace but this post seems to not mention to replace the electrolytic one only to replace. Is it the two 12uF electrolytic and mylar caps caps that should be replaced or just do all three for both x-overs?

 

[59ctd]

Looking at Parts Express it looks like the metalized polypropylene caps are in the budget range so I'll replace all six of them. Regarding the (yes very old) post I linked above I was a bit confused as to why the recommendation to replace the inductance coil. I was not expecting that to need replacing.

 

[Verdinut]

Looking at Parts Express it looks like the metalized polypropylene caps are in the budget range so I'll replace all six of them. Regarding the (yes very old) post I linked above I was a bit confused as to why the recommendation to replace the inductance coil. I was not expecting that to need replacing.

You don't need to replace the inductor and neither any non-electrolytic cap. For the difference in cost, I agree that it is wise to make replacement with the polypropylene type.

 

[lovinthehd]

Be interesting if you measured each of the caps you're taking off the board....

 

[59ctd]

Be interesting if you measured each of the caps you're taking off the board....

It looks like my old multimeter does measure up to 20uF max so I will indeed measure those caps when I take them off and compare to the new ones.