Electrolytic cap replacement-RT7 crossover

speakergeek
speakergeek Posts: 555
edited July 2013 in Vintage Speakers
Can you guys recommend a superior capacitor replacement for the 9.0 uf electrolytic cap in this crossover? Also what is the crossover frequency? Thanks!!!!
Post edited by speakergeek on
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  • Tbone289
    Tbone289 Posts: 661
    edited January 2013
    I would recommend removing the bypass cap and using two 4.7uf caps in parallel to replace C2 & C3. 9.0uf are harder to find and don't fit the stock terminal cup as well as the smaller 4.7uf in parallel. This will still keep you within 2% of the stock 9.47uf (C2+C3) spec. A bypass cap is not needed, nor even desired, if good-quality poly caps are used.

    See my RT7 upgrade pictorial at the link below. I have since put the stock inductor back in, because the one I used for the mod didn't match stock DCR:

    http://www.polkaudio.com/forums/showthread.php?123464-RT7-crossover-upgrade-pictorial


    If I were to do it again, I would use Clarity caps rather than Dayton. I've used Clarity PX caps a few times since I did the RT7 upgrade, and they sound great even at their modest price point. If cost isn't as much of a concern, I would use a higher-grade Clarity brand or Sonicaps.

    http://www.madisoundspeakerstore.com/px-cap-250vdc/claritycap-4.7-mfd-px-range-polypropylene-caps/


    EDIT: I've never calculated the crossover frequency. I figured Polk got it right, so I just stayed within spec.
    2.1: PC>Schiit Gungnir MB>Schiit Freya Noval>NAD C-270>Ascend Acoustics Sierra-1, HSU STF-2 5.1: HDMI Bitstream>Denon AVR-1910>polkaudio RTE55, CS350-LS, RT3, HSU STF-2, Visio M55-F0
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  • thsmith
    thsmith Posts: 6,082
    edited January 2013
    What Tbone said but I will throw in sonicap as another cap option.
    Speakers: SDA-1C (most all the goodies)
    Preamp: Joule Electra LA-150 MKII SE
    Amp: Wright WPA 50-50 EAT KT88s
    Analog: Marantz TT-15S1 MBS Glider SL| Wright WPP100C Amperex BB 6er5 and 7316 & WPM-100 SUT
    Digital: Mac mini 2.3GHz dual-core i5 8g RAM 1.5 TB HDD Music Server Amarra (memory play) - USB - W4S DAC 2
    Cables: Mits S3 IC and Spk cables| PS Audio PCs
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  • Tbone289
    Tbone289 Posts: 661
    edited January 2013
    Tbone289 wrote: »
    This will still keep you within 2% of the stock 9.47uf (C2+C3) spec.

    I miscalculated there. 2 4.7 caps would keep you within 1% of the 9.47uf spec with the bypass removed.
    2.1: PC>Schiit Gungnir MB>Schiit Freya Noval>NAD C-270>Ascend Acoustics Sierra-1, HSU STF-2 5.1: HDMI Bitstream>Denon AVR-1910>polkaudio RTE55, CS350-LS, RT3, HSU STF-2, Visio M55-F0
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  • thsmith
    thsmith Posts: 6,082
    edited January 2013
    4.7uF / 200VDC 0.92 x 1.27 $12.87


    http://www.soniccraft.com/sonicaps.htm

    Put them in parrallel like this.

    P9260263.jpg
    Speakers: SDA-1C (most all the goodies)
    Preamp: Joule Electra LA-150 MKII SE
    Amp: Wright WPA 50-50 EAT KT88s
    Analog: Marantz TT-15S1 MBS Glider SL| Wright WPP100C Amperex BB 6er5 and 7316 & WPM-100 SUT
    Digital: Mac mini 2.3GHz dual-core i5 8g RAM 1.5 TB HDD Music Server Amarra (memory play) - USB - W4S DAC 2
    Cables: Mits S3 IC and Spk cables| PS Audio PCs
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  • Tbone289
    Tbone289 Posts: 661
    edited January 2013
    If you use the pictures in the RT7 upgrade link I posted above, you can see one way to mount them to fit in parallel on the RT7 board.
    2.1: PC>Schiit Gungnir MB>Schiit Freya Noval>NAD C-270>Ascend Acoustics Sierra-1, HSU STF-2 5.1: HDMI Bitstream>Denon AVR-1910>polkaudio RTE55, CS350-LS, RT3, HSU STF-2, Visio M55-F0
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  • westmassguy
    westmassguy Posts: 6,850
    edited January 2013
    speakergeek wrote: »
    Can you guys recommend a superior capacitor replacement for the 9.0 uf electrolytic cap in this crossover? Also what is the crossover frequency? Thanks!!!!
    Sonicap makes the 9uf and 2.2 uf cap, no need to parallel anything, and ditch the .47 Mylar. While you're at it, order 1 ohm Mills MR-12 resistors too.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
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  • F1nut
    F1nut Posts: 50,552
    edited January 2013
    westmassguy wrote: »
    Sonicap makes the 9uf and 2.2 uf cap, no need to parallel anything, and ditch the .47 Mylar. While you're at it, order 1 ohm Mills MR-12 resistors too.

    ^This^
    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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  • Tbone289
    Tbone289 Posts: 661
    edited January 2013
    Indeed, if you can make the 9uf fit, it's the better option. I couldn't, so I went with the parallel 4.7's. Not using the bypass cap has obviously been covered.
    2.1: PC>Schiit Gungnir MB>Schiit Freya Noval>NAD C-270>Ascend Acoustics Sierra-1, HSU STF-2 5.1: HDMI Bitstream>Denon AVR-1910>polkaudio RTE55, CS350-LS, RT3, HSU STF-2, Visio M55-F0
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  • speakergeek
    speakergeek Posts: 555
    edited February 2013
    So I ended up doing a prretty major change to this speaker. I can say that it was most definitely a change for the better. I initially got carried away with the c/o design possibilities, so I just decided to upgrade the c/o and the drivers. I went the SEAS tweats and woofs plus a custom c/o from Madisound. Here are some shots of the build:

    DSC_0018_zpsb18c559c.jpg

    DSC_0019_zpsca123c2a.jpg

    DSC_0039_zpsdf248d66.jpg

    The cross-over consists of ESA Clarity Caps in the tweeter circuit and a Goertz 14g copper inductor plus SoniCap Fast Caps in the woofer circuit. Also the resistors are Mundorf MOX. All inductors are air core. Sounds absolutely great! Cheers.
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  • Face
    Face Posts: 14,340
    edited February 2013
    I'd say that's a big upgrade. Congrats!
    "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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  • speakergeek
    speakergeek Posts: 555
    edited February 2013
    Face wrote: »
    I'd say that's a big upgrade. Congrats!

    Yes sir! The overall improvement in SQ has been profound. Thank you for the compliment.:cool: Trying to describe the change is difficult, but simply put the speakers seem much larger with considerably better mids and highs.
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  • Face
    Face Posts: 14,340
    edited February 2013
    It's hard to tell from your image, but is the tweeter flush mounted? If not, and you're capable of doing so, flush mounting would make them sound even better.
    "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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  • speakergeek
    speakergeek Posts: 555
    edited February 2013
    Face wrote: »
    It's hard to tell from your image, but is the tweeter flush mounted? If not, and you're capable of doing so, flush mounting would make them sound even better.

    I'm working towards that very goal. I want to do it right. I realize there are phase lobe issues etc. but even so, they new arrangement sounds great. My mains have a slight tilt backwards already.
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  • Face
    Face Posts: 14,340
    edited February 2013
    If you know how to use a router, this kind of bit may help: http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bit_rabbet.html#rabbeting6_kit_anchor
    "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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  • F1nut
    F1nut Posts: 50,552
    edited February 2013
    The cross-over consists of ESA Clarity Caps in the tweeter circuit and a Goertz 14g copper inductor plus SoniCap Fast Caps in the woofer circuit.

    That's not a Sonicap, it's a Solen.
    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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  • speakergeek
    speakergeek Posts: 555
    edited February 2013
    F1nut wrote: »
    That's not a Sonicap, it's a Solen.

    Yes you are correct. My bad....:redface:
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  • westmassguy
    westmassguy Posts: 6,850
    edited February 2013
    Very nice work, but technically it's no longer a Polk
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
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  • speakergeek
    speakergeek Posts: 555
    edited February 2013
    westmassguy wrote: »
    Very nice work, but technically it's no longer a Polk

    You are correct. I like the cabinet though. Keeping it in place really emphasized the difference in upgrade though.
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  • speakergeek
    speakergeek Posts: 555
    edited February 2013
    I did rename these speakers. Now they are CS-7 mk.1...:cheesygrin:
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  • speakergeek
    speakergeek Posts: 555
    edited February 2013
    Face wrote: »
    It's hard to tell from your image, but is the tweeter flush mounted? If not, and you're capable of doing so, flush mounting would make them sound even better.

    Here is a short term "flush mount solution" I came up with. I cut a diffraction baffle from cardboard and covered it with a thin coat of black colored wool. Honestly I think it sounds better than before-possibly better than pure flush mount? THoughts and speculations please. Don't chew me up too bad...:eek:

    DSC_0027_zpsc2368264.jpg
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  • Face
    Face Posts: 14,340
    edited February 2013
    It will probably help, but still isn't correct. :)
    "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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  • speakergeek
    speakergeek Posts: 555
    edited February 2013
    Face wrote: »
    It will probably help, but still isn't correct. :)

    How much incorrectness will be corrected?.....??:razz: Honestly, I'm haapy with the result so far...
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  • DON73
    DON73 Posts: 516
    edited February 2013
    Many years ago I bought a pair of RT5s and when I heard them in my home I thought "these are the easiest listening speakers I own" Packed them up and rushed back to the store to trade for what I assumed would be an even better speaker the RT7s. Rushed
    home listened then packed the RT7s up and rushed back to get my RT5s back but they were sold.
    TO ERR IS HUMAN. TO FORGIVE IS CANINE.
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  • speakergeek
    speakergeek Posts: 555
    edited February 2013
    DON73 wrote: »
    Many years ago I bought a pair of RT5s and when I heard them in my home I thought "these are the easiest listening speakers I own" Packed them up and rushed back to the store to trade for what I assumed would be an even better speaker the RT7s. Rushed
    home listened then packed the RT7s up and rushed back to get my RT5s back but they were sold.

    The RT7 was a great speaker for many years for me. Recently though the sibilance and mids that used to be were gone. Thought it could be the electolytic cap in the crossover being bad, or possibly just the tweets wearing out. Started exploring the possiblity of rebuilding the crossover, then just decided to upgrade the entire speaker set and get a good crossover to go with them. So far very happy with the result, although I no longer have true Polk Audio speakers any more.
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  • DON73
    DON73 Posts: 516
    edited February 2013
    speakergeek wrote: »
    The RT7 was a great speaker for many years for me. Recently though the sibilance and mids that used to be were gone. Thought it could be the electolytic cap in the crossover being bad, or possibly just the tweets wearing out. Started exploring the possiblity of rebuilding the crossover, then just decided to upgrade the entire speaker set and get a good crossover to go with them. So far very happy with the result, although I no longer have true Polk Audio speakers any more.






    You did a fine job on all the modifications! Doesn't matter what they are now.......your enjoyment of them is what's important.
    TO ERR IS HUMAN. TO FORGIVE IS CANINE.
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  • speakergeek
    speakergeek Posts: 555
    edited February 2013
    DON73 wrote: »
    You did a fine job on all the modifications! Doesn't matter what they are now.......your enjoyment of them is what's important.

    Thanks man! The latest configuration has given me several grins...
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  • speakergeek
    speakergeek Posts: 555
    edited July 2013
    A couple more shots of this speaker. I've been tweeking it along the way. Went to dual binding posts since crossover allows; Man these speakers sound very good! I'm not bi-wiring them yet, but I do plan to.

    DSC_0052-001_zpsf926c2e0.jpg

    DSC_0017-001_zps6c052e68.jpg
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  • 101159
    101159 Posts: 1
    Tbone289 wrote: »
    I would recommend removing the bypass cap and using two 4.7uf caps in parallel to replace C2 & C3. 9.0uf are harder to find and don't fit the stock terminal cup as well as the smaller 4.7uf in parallel. This will still keep you within 2% of the stock 9.47uf (C2+C3) spec. A bypass cap is not needed, nor even desired, if good-quality poly caps are used.

    See my RT7 upgrade pictorial at the link below. I have since put the stock inductor back in, because the one I used for the mod didn't match stock DCR:

    http://www.polkaudio.com/forums/showthread.php?123464-RT7-crossover-upgrade-pictorial


    If I were to do it again, I would use Clarity caps rather than Dayton. I've used Clarity PX caps a few times since I did the RT7 upgrade, and they sound great even at their modest price point. If cost isn't as much of a concern, I would use a higher-grade Clarity brand or Sonicaps.

    http://www.madisoundspeakerstore.com/px-cap-250vdc/claritycap-4.7-mfd-px-range-polypropylene-caps/


    EDIT: I've never calculated the crossover frequency. I figured Polk got it right, so I just stayed within spec.

    TBONE - your brilliant tutorial is gone! I did your mod in 2013, but now one side of my RT7 is down a tweeter again (switched it with the other, still no good) and I want to do the upgrade again, but the original crossover upgrade pictorial is gone!!

    Do I need to also get a new 2.2uF to wire in with the 4.7's?
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