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  1. #1

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    Question Schematics neededfor Polk RT55i

    Does anyone have the schematics for the Polk RT55i? I have a pair and would like to upgrade the crossovers but have no idea what components are in there. Checked the stickys and they do not have the RT55is. Thanks in advance.


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    you might just be able to remove the crossover from your speakers and see what's in there. i know this isn't exactly the best way.. but it might give you an idea of what's needed.

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    I removed the crossover from the RT55is. It looks pretty simple but I need help in identifying the caps... the red square one says .47J100, the yellow one is a 3.0J100 and the cans are 9.5mf50v and a 16.5mf50v...

    so am I right to assume they are...
    .47uf 100V
    3.0mf 100V
    9.5mf 50V
    16.5mf 50V

    They seem pretty cheap parts on the board, but equivalent Sonicaps are
    .47f $7.80
    3.0mf $8.95
    9.1mf $17.45
    17mf $25.40

    or a whopping $60.00/speaker... ouch!!!

    Plus the problem of fitting all the components on the crossover board...
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  4. #4

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    it's usually a pretty tight fit getting the new parts on the board again. but it can be done.

    good sound isn't cheap.. if those RT55i's were mine. i'd spend the $ to get them done.. the 55i's have a pretty decent following. or used to anyways.

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    Well, Soniccraft is having a 20% off sale right now, so it would be a bit cheaper:)

    No offense, but I'm not sure the RT55i deserves a full Sonicap treatment. There are cheaper alternatives that would offer improvements over the stock electrolytic caps. Jantzen Cross Caps, Dayton Metalized Poly caps, or some maybe ClarityCaps. Also, its not just the caps. When you are in there, you should replace the stock resistors with Mills non-inductive resistors.

    There has been a lot of discussion here on whether the bass shunt capacitors (the larger value electrolytics) have much effect on the quality of sound. Some say that all Sonicaps are a must, others (like me) say that cheaper metalized poly caps are good enough for the bass shunt caps. Ultimately, you will have to decide how much money you want to sink into those speakers. Perhaps use Sonicaps in the tweeter circuit, Daytons in the bass circuit and use the mills resistors in both.

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    can anyone tell me if the TI47j100 cap is a bypass cap?

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    Quote Originally Posted by jon s View Post
    can anyone tell me if the TI47j100 cap is a bypass cap?
    Hard to say without a schematic. You should be able to trace the circuit board and draw out the wiring. They were usually pretty simple.

    I would have thought the RT55i shared a similar crossover to the RT800, but when I checked that scat, it was clearly different. Evidently Polk implemented a band pass for one of the woofers or used a higher order design because the 55i is clearly more complex than the 800.

    EDIT: After looking at your pictures closer, I would say, yes, for sure the red .47 cap is a bypass for the black 8uf cap. They are wired in parallel to each other and are part of the tweeter circuit.
    Last edited by billbillw; 03-05-2009 at 11:09 AM.

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    would you be able to tell me which components are for the tweeter and which ones are for the mid-woofers? That way I can determine which caps to replace with the Sonicaps.

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    I would replace the 3 and 9.5uf caps with Sonic Caps, and replace the 16.5uf with Dayton. If you call Sonic Craft, they can send you custom values.
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche

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    Since Soniccraft has a 20% sale, I went all Soniccaps and Mills... came out $90... going Daytons would have saved me about $20 but separate shipping from Parts Express would have cut that to $10 so I figured why not... go all Soniccaps... I sure hope that 0.47mf cap is a bypass...

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    The difference should be more than subtle, enjoy!
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche

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    Just wondering, the photo shows that black as a 9 mfd, but your original post said 9.5. I do not see a decimal in the photo.

    The .47 is definitely a bypass.
    Last edited by billbillw; 03-05-2009 at 04:18 PM.

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    my mistake on the 9.5.... I was thinking about the 16.5 when I was typing away...

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    After going over the crossover closely, the .47mf cap is definitely a bypass cap. I removed it and the speakers sound marginally more detailed... i am still awaiting my Sonicaps....

    After seriously listening to the RT55is, I can say that the speakers are not accurate. Some music reveals a slight coloration, especially when listening to strings or piano.

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    Just so you know, bypass caps are not necessarily a bad thing, especially when used in conjunction with electrolytics (as is the case with your RT55i). That little poly cap you took out probably had a much better sound than the electrolytic you left in. You should also realize that the .47uf capacitance you took out will affect the crossover point. Caps in parallel are additive. In other words, the correct caps size for that part of the circuit is 9.0+.47 or basically 9.5uf. That is more than 5% difference. What size Sonicap did you order to fill in that spot? 9.5 or 9.1?

    The criticism that by-pass caps get around here are usually talked about when you take a good poly cap (Sonicap or similar) and bypass with a very small (.1uf or similar) film/foil cap. The film/foil caps are supposed to sound better and bypassing can impart some of that sound to the circuit, but many find the sound un-natural and do not like it.

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    I am replacing it with a 9.1uf cap as they did not have a 9.5 available... will see what happens...

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    Well, I got the Sonicaps in yesterday. Looks like upgrading the crossover will be a lot more challenging that expected. Most of the components other than the 16.5 and 9uf caps are surface mounted, the leads do not go thru the circuit board. the 9uf and 16.5uf caps are adjacent to each other and of course the Soniccaps are huge. I have to be careful to make sure the crossover can go back into the opening so the caps have to fit within the board dimensions.

    My current idea is to buy risers to raise the board to be able to fit the caps under the board. Will insert photos when time permits...

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    Surface mount? From what I see, everything is through board, not surface mount. That would be VERY VERY unusual to have surface mounted crossover parts. That is usually only found with micro-electronics. I think you just need to de-solder everything and get a better look. Do you have solder wick or a solder sucker?
    For the large caps, you will need to run some type of jumper.

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    Well, it's not real surface mounted. But the two resistors and the 3uf cap are soldered to the top of the board only. The leads do not go thru to the other side, the underside of the board has no holes except for the .47, 9 and 16.5 caps....

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    Did you see this thread BTW, in case it helps?

    http://www.polkaudio.com/forums/show...50&postcount=1

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    Thanks for the link Kex... I did my crossover layout exactly the same way with some changes. I had to lift the 3uf cap a bit since the leads end up under the cap and soldering it was a bit difficult. Also, Polksaladanni did not use any glue to minimize any vibrations of the caps but I did. The 9uf did not fit under the board completely so it overhangs a bit.

    After doing the changes, you really have to be careful as some of the leads can short over other wires unless you insulate them.

    I must admit I am pleasantly surprised at the sound with the Soniccaps. It's way too early to see how much of a change there will be in the end but immediate improvements were noticeable. The top end was a LOT smoother, not as harsh as before. Instruments can easily be isolated from each other, not smeared on a flat plane. Depth is slightly improved. Coloration has been reduced. Their is a sense of "air" or ambience in the sound. If the speakers had a bit more bass, it would be almost perfect.

  22. #22

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    DOH!!! WIth the 3.0 cap floating 1/4" so I can solder the leaders under the cap, I just realized I can just apply some hot glue near the bottom and bend the cap against the board and glue... now it's nice and snug...

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