Jumping in the water again... Polk RTA-12Bs...

jon s
jon s Posts: 905
edited August 2011 in Vintage Speakers
Well, after sadly selling the Polk SDA-1Bs last week, I am about to buy a pair of Polk RTA-12Bs or 12Cs... seller not sure which one he has. he said it has been in storage for several years in a spare bedroom and they are in good shape. I just could not get the hang of the SDA effect. i know that the SDAs restore ambiance in the music but sometimes it sounding like the music was in a reverb or echo chamber. This was of course due to the "added" effects many mixers did when doing their thing.

Anyway, back to the subject at hand. Of all the Polks, the RTA-12B/Cs really piqued my interest the most. I (as some of you know) just picked up a pair of Model 10Bs and really love it. After replacing all the caps and resistors in the crossovers, I must admit that the sound stage and imagery is to die for.

Now with the probable purchase of the 12s (which I heard was a great step above the 10s) I am about to tackle and upgrade the crossovers again. Has anyone done so and can they tell me how hard they were to upgrade? I see that the 12s have a crossover on the top of the cabinet. Is there a space problem after the caps are replaced? Are there any crossovers in the cabs themselves (I assume so)? If anyone has upgraded the crossovers on the 12s, i would appreciate any tips beforehand. thanks in advance...
Post edited by jon s on
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Comments

  • tx_polkhead
    tx_polkhead Posts: 248
    edited June 2008
    I don't remember seeing any additional CO parts inside. Take tons of pics and notes along the way. I would love to hear how this project turns out.
    Abel
    Polk Audio RTA 12c's, Monitor 7c, Monitor 5JR+, SDA CRS+
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  • danger boy
    danger boy Posts: 15,722
    edited June 2008
    I think you're really going to enjoy those RTA 12's... they are a very nice sounding speaker.
    PolkFest 2012, who's going>?
    Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin:
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  • jon s
    jon s Posts: 905
    edited June 2008
    I just picked up the Polk RTA12s and they are the model 12Cs... they are in pretty good condition with a couple of issues... one of the speakers are missing the pins that hold the top grill in place, they are snapped off at the base... where can I get some replacements?

    the bigger problem is one of the speakers is possibly blown. the crossover is covered with soot, the protective relay is blown out. Don't know about the condition of the tweeter itself or the mid-bass drivers. see the attached pictures... any advice would be appreciated...

    :(

    I noticed that the crossover board does not match the RTA12B posed in the speaker forum but it does match the Monitor 12 crossover board. the crossover diagrams do not show any of the resistors as seen on the circuit board.
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  • ben62670
    ben62670 Posts: 15,969
    edited June 2008
    Bypass the Poly Switch(little blue disk), and see if you have output from the tweeter. If you don't swap the tweeter from the other channel to this speaker, and see if it works.
    Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • danger boy
    danger boy Posts: 15,722
    edited June 2008
    with the exception of the burned crossover.... those are minty looking.. the broken off pegs that the hat sits on.. are pretty common. Polk used to carry them.. not sure if they still do or not. call em up.

    so what is the burned up part of the crossover? can you post a picture of them both side by side?
    PolkFest 2012, who's going>?
    Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin:
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  • F1nut
    F1nut Posts: 50,566
    edited June 2008
    I just could not get the hang of the SDA effect. i know that the SDAs restore ambiance in the music but sometimes it sounding like the music was in a reverb or echo chamber. This was of course due to the "added" effects many mixers did when doing their thing.

    So, it wasn't that the wife didin't like them, eh!?!

    I'd say there was something wrong with the pair you had.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • jon s
    jon s Posts: 905
    edited June 2008
    F1nut wrote: »
    So, it wasn't that the wife didin't like them, eh!?!

    I'd say there was something wrong with the pair you had.

    no.. nothing was wrong with the SDA-1Bs... just was not my cup of tea and my wife definitely said they had to go... the 12Cs are almost as big... I might have a problem keeping them too... I am planning to upgrade the crossovers. Is there a crossover in the cabinets? the schematics posted do not mention anything about separate crossovers. Also, is it recommended to replace the tweeters with the newer silk domes? I have a pair of silk domes backordered for my Model 10Bs, I might just pop them in the 12s instead when they come in...
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  • ben62670
    ben62670 Posts: 15,969
    edited June 2008
    The whole XO is external on your 12's, and definitely ditch the SL2000's. You should be able to get around $20 each for them on Ebay.
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • F1nut
    F1nut Posts: 50,566
    edited June 2008
    jon s wrote: »
    no.. nothing was wrong with the SDA-1Bs.

    You indicate otherwise......
    jon s wrote: »
    I am beginning to suspect there may be a problem with the left speaker... I have felt that the bass on the SDA1Bs seem to be rather weak. Did a test tone sweep on both speakers. It appears that the passive radiator on the left speaker does not pulse as much as the right one on lower frequencies. It also appears that the lower stereo speaker does not move as much as the upper one. The right speakers seem to pulse synchronously. The left ones do but the lower one does not move as much. Placing my ear next to the lower driver does hear sound. Any ideas? Crossover or bad speaker...

    I'm telling you that, "sometimes it sounding like the music was in a reverb or echo chamber" is not normal for SDA speakers and they do not compromise the fidelity one little bit. Therefore, based on your own comments, something was wrong with your ex-SDA's.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • ben62670
    ben62670 Posts: 15,969
    edited June 2008
    You can clean those boards with rubbing alcohol;)
    Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • jon s
    jon s Posts: 905
    edited June 2008
    F1nut wrote: »
    You indicate otherwise......



    I'm telling you that, "sometimes it sounding like the music was in a reverb or echo chamber" is not normal for SDA speakers and they do not compromise the fidelity one little bit. Therefore, based on your own comments, something was wrong with your ex-SDA's.

    What I meant was there was nothing physically wrong with them. It's just that the SDA effect bothers me to some degree on some recordings. In fact, if you look at some of the reviews of the SDA speakers, some of the reviewers specifically mentioned that the speakers exhibited some unwanted side effects on heavily mixed tracks.

    Getting back to the RTA-12Cs. I see that the 12Bs (I cannot find any schematics for the 12Cs and the circuit looks similar to the 12Bs) has four 27uF and two 4.4 caps on each side (and it appears there is a XO in the cabinet for one of the mid-bass drivers which has two of the 27uF caps and a resistor. I was contemplating getting the Sonicaps but the 27uF is about 1.5x3 inches in size which is WAY to big for the pcb. I could stand the cap vertically but I don't think the grill cover on the top will clear the cap so I guess the Sonicaps are out. Solens make a 4.4uf cap but they are not recommended. i will probably get a pair of Jantzen superior 2.2uF cap (they are 0.75x1.5 inches) and put them in parallel. Or should I get a 4.0 or 4.7 uf cap, they wud appear to be too far out of spec.

    Secondly, if the midbass drivers are damaged, are they available from Polk (what is the model number)? is there a parts list for the RTA12c? The parts list i found on the site shows only the monitor 10s and earlier but not the 12s.
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  • Face
    Face Posts: 14,340
    edited June 2008
    How about using Dayton for the large values and Sonic Caps for the small values, or Dayton all around(if they fit)? From my person experience, I would avoid Solen on the small values. From what I read, avoid the cheap Jantzen's on the small values also.

    If you have a bad driver, pull it from the enclosure and look at the back. Most of them have the part number written on them.
    "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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  • jon s
    jon s Posts: 905
    edited June 2008
    I used the Jantzens on my Polk Model 10Bs and I liked them... not sure if this makes sense but it is true...

    I go to a stereo shop in the 90s... I said "gee... something wrong with the setup in here... everything has a faint ringing noise."

    clerk says "I don't hear anything... maybe you shud get your ears checked?"

    Go to ear doctor.. I got tinnitus and it just happened to be worse that day. So now I have a constant ringing sound in my ears now... that's what happens when you work near airplanes everyday with inadequate ear protection. my hearing response is like a trough... i can hear the bass and treble pretty well (with the exception of the slight ringing) but the midrange dips down so I have a hard time listening in on conversations... don't mess around in noisy areas... once you lose your hearing... you can't enjoy the music.
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  • Face
    Face Posts: 14,340
    edited June 2008
    If you're happy with the way they sound, that's all that matters, enjoy them.

    Sorry to hear about your hearing, my g/f has the same issue.
    "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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  • jon s
    jon s Posts: 905
    edited June 2008
    so, has anyone mounted sonicaps on the RTA12s and if so, how did they mount it... the sonicaps are humongous.. 1.5x3" compared the the originals...

    also was thinking... the slanted plate in front of the tweeter is supposed to eliminate diffraction between the tweeter and the cabinet.. maybe I should put some sort of felt lining on it. the felt would absorb any soundwaves glancing off the plate...
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  • jon s
    jon s Posts: 905
    edited June 2008
    ben62670 wrote: »
    The whole XO is external on your 12's, and definitely ditch the SL2000's. You should be able to get around $20 each for them on Ebay.

    looking at the schematic for the 12Bs, there must be another crossover in the cabinet... the parts list does not match otherwise. I think there are two 27uf caps in the cabinet for that cascaded crossover (one midbass driver crosses at 600Hz and the other at 2000Hz)...
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  • jon s
    jon s Posts: 905
    edited June 2008
    I just bypassed the blown polycap and hooked the speaker up to an amp... the tweeter was silent. the tweeter does show continuity when hooked up to a ohm meter so I don't think the problem is there. just as a precaution I hooked up another tweeter in its place and still nothing. any ideas where the problem might be?
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  • dcmeigs
    dcmeigs Posts: 708
    edited June 2008
    Jon,

    I just looked at the schematic for the rta12b. That's a pretty interesting crossover; pretty complex. But if you have no signal, I'm betting that the first 4.4 uf mylar cap (that is not in parallel with the 55uf) is probably bad. You can test it with a VOM on ohm scale but you will need to desolder it or the bypass cap first. To check it with the VOM, place the leads across the cap and watch the meter. It should start with a low reading and charge up to 1. When they are bad they don't charge up.

    Which Island are you on? I will be sailing around the islands of Hawaii and Maui starting the 16th, I could probably give you a hand with it if you are still stumped.
    The world is full of answers, some are right and some are wrong. - Neil Young
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  • dcmeigs
    dcmeigs Posts: 708
    edited June 2008
    One other thought. There would probably be no harm in just using an alligator clip to bypass that cap momentarily for testing purposes. Keep the volume low. If you get sound, I'd replace that cap.
    The world is full of answers, some are right and some are wrong. - Neil Young
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  • jon s
    jon s Posts: 905
    edited June 2008
    I live on Oahu... if you make a port call here, let me know... maybe we can get together.

    I decided to replace all the caps and resistors on the crossover board since its due for an overhaul. basically, I will be replacing everything on the crossover except for the inductor coils. i will use Sonicaps for the four 4.4uf and Jantzen four the eight 27uf caps and the two 55uf caps, Mills for the four resistors and Relcaps for all the 750pf caps... for a total cost of $200...

    There is one 2-ohm 5 watt resistor on the crossover board which I cannot find in the schematics. You can see it right below the blown polyswitch on the board. I am also bypassing the polyswicthes completely.

    If I went all Sonicaps, I think I will have clearance issues (since the crossover is external and sits on the top of the cabinet under the grill) as i would use a total of six 27uf caps per crossover and they are large, 3" x1.7", and at $35 each, total about $420 just for the 27uf caps alone. I just could not justify spending more than $500 on the crossover components.
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  • F1nut
    F1nut Posts: 50,566
    edited June 2008
    Once again Jon, do NOT replace the 750pF bypass caps, they are not needed and will make the high frequencies sound un-natural.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • jon s
    jon s Posts: 905
    edited June 2008
    F1nut wrote: »
    Once again Jon, do NOT replace the 750pF bypass caps, they are not needed and will make the high frequencies sound un-natural.

    so you are recommending to just to remove the 750pf caps completely then...
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  • Face
    Face Posts: 14,340
    edited June 2008
    Yes he is.
    "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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  • jon s
    jon s Posts: 905
    edited June 2008
    Shucks... I ordered those 750pf caps from Soniccraft already... $36 wasted...
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  • F1nut
    F1nut Posts: 50,566
    edited June 2008
    Send them back.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • schwarcw
    schwarcw Posts: 7,338
    edited June 2008
    Jesse is right, you really don't need them. I tried my SRS 2.3's with and without the 0.1 uF by pass cap. Honestly, I couldn't hear a difference either way. A few members here reported better sonics without the bypass cap. Pretty good evidence that these are not needed with the faster film caps in use today. With the older electrolytic caps, the bypass cap was probably needed. Jeff will take them back. Call Elliott in the order Department, you probably don't even need to talk with Jeff.
    Carl

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  • Boywonder
    Boywonder Posts: 225
    edited June 2008
    Jon: I replaced the broken locating pins for the tophats on my RTA-12C's with std grill headlocks that I had in my parts drawer. I believe that you can get them from Parts Express or Madisound. IIRC, I also ordered exact repalcements from Polk (back in January) for one of the cabinets; the Polk ones have the ability for the ball to move radially compared to the body, which may help align the top hats to the sides of the cabinet better, although the generic grill headlocks that I used worked just fine.
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  • dcmeigs
    dcmeigs Posts: 708
    edited June 2008
    jon s wrote: »
    I live on Oahu... if you make a port call here, let me know... maybe we can get together.

    Love to. Problem is, it's very difficult to find a transient slip for the boat in Oahu. If you happen to hear of anyone who will have an open slip for a few days during the last two weeks of July, I'd sure like to hear about it.
    The world is full of answers, some are right and some are wrong. - Neil Young
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  • jon s
    jon s Posts: 905
    edited June 2008
    Boat slips are very hard to find on Oahu, in fact this year is worse than normal as the state needs to do some maintenance work and the boats have to be relocated.
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  • jon s
    jon s Posts: 905
    edited July 2008
    Well, I finally made a decision... I am going to replace the caps in the upper crossover with Sonicaps. The caps in the cabinet will be replaced with cheaper Jantzens until I can afford to replace them with the Sonicaps. Right now, it's setting me back about $400. Replacing the LF caps with Sonicaps will be another $150 later. i think the RTA-12Cs have one of the most complex crossovers. There are nine caps on each speaker...
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