Caps for Monitor 7B crossover

billinrio
billinrio Posts: 8
edited November 2009 in Vintage Speakers
Hi,

This is my first post on this forum, which I´m very happy to have discovered. I live in Brazil, and I bought my first Polks in Washington DC in 1980 - a pair of Monitor 7Bs, and I still enjoy listening to them. They are great, and have survived several international moves and (thanks to the rubber surrounds) the intense heat and humidity during the last 20 years in Rio de Janeiro. About 10 years after I bought them, one of the tweeters went out, and the Washington DC dealer then sold me a replacement that has the Polk logo, but a brushed silver base and a translucent dome that are different from the original. So, my pair of Monitor 7Bs are running with different tweeters.

Recently, the other one of the pair began to produce very reduced and distorted output fromthe woofer. I suspect that I need to replace the crossover capacitors. I discovered that a seller on eBay (http://cgi.ebay.com/Polk-Audio-Monitor-5-7-RTA-8T-Upgrade-Kit_W0QQitemZ260502434325QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3ca727b215) offers cap replacements. I would very much appreciate any opinions on this option.
Post edited by billinrio on
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Comments

  • madmike
    madmike Posts: 81
    edited November 2009
    Depending on how much you want to spend, you could check out http://www.madisound.com/catalog/index.php?cPath=404_5_351 . They have replacement resistors also. There are a few topics on here on X-Over upgrades for 5B's. They are fairly easy to do if you can solder. By the way welcome to the forum billinro. I'm sure others will chime in soon.
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  • Crazylitvak
    Crazylitvak Posts: 38
    edited November 2009
    I've bought his replacement kits for my monitor 7 & 10's. I was very pleased and now just bought a set of caps directly from Madisound for my sons Polks 7's. The new caps cleaned up the mudiness. For someone like me who is electronically illiterate but yet know how to solder, the kits were the way to go.
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  • billinrio
    billinrio Posts: 8
    edited November 2009
    Thank you for your replies to my post. I just received an e-mail from the eBay seller of the capacitor replacement kit (his name is Ray). He says that "A faulty capacitor in the crossover will not not cause little output from the woofer. I suspect, you have either a faulty woofer or amplifier. Is this correct? If so, where should I look in order to find a replacement woofer for my Monitor 7B?
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  • Face
    Face Posts: 14,340
    edited November 2009
    Polk still sells replacement drivers. Remove the driver, read the part number off the back, and give Polk a call. Be sure to mention that you're a Club Polk member for a discount.

    As for that kit, I would pass. You could do a lot better for only a little more.
    "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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  • billinrio
    billinrio Posts: 8
    edited November 2009
    Except for the "Polkaudio" logo, the printing on the back of the woofer is illegible. On the front rubber suspension,there is "polk" and "SR142/17". Might the latter be the part number?
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  • Face
    Face Posts: 14,340
    edited November 2009
    Pull the other woofer. It should should out with MW65 followed by two more numbers, 00, 02, etc...
    "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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  • billinrio
    billinrio Posts: 8
    edited November 2009
    With a jeweler´s loup I can just make out "Monitor Series Driver MW8 (maybe 6) 500"
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  • Face
    Face Posts: 14,340
    edited November 2009
    It's a MW6500. They're still available as far as I know.
    "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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  • skrol
    skrol Posts: 3,393
    edited November 2009
    I recently spoke to Polk CS about the MW6500 replacement. They no longer have the MW6500 but the MW6503 is a compatible replacement. I was told that they have the same theil small parameters.
    Stan
    Stan

    Main 2ch:
    Polk LSi15 (DB840 upgrade), Parasound: P/LD-1100, HCA-1000A; Denon: DVD-2910, DRM-800A; Benchmark DAC1, Monster HTS3600-MKII, Grado SR-225i; Technics SL-J2, Parasound PPH-100.

    HT:
    Marantz SR7010, Polk: RTA11TL (RDO198-1, XO and Damping Upgrades), S4, CS250, PSW110 , Marantz UD5005, Pioneer PL-530, Panasonic TC-P42S60

    Other stuff:
    Denon: DRA-835R, AVR-888, DCD-660, DRM-700A, DRR-780; Polk: S8, Monitor 5A, 5B, TSi100, RM7, PSW10 (DXi104 upgrade); Pioneer: CT-6R; Onkyo CP-1046F; Ortofon OM5E, Marantz: PM5004, CD5004, CDR-615; Parasound C/PT-600, HCA-800ii, Sony CDP-650ESD, Technics SA 5070, B&W DM601
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  • billinrio
    billinrio Posts: 8
    edited November 2009
    Thanks very much for the information.
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  • billinrio
    billinrio Posts: 8
    edited November 2009
    According to a post in the AudioKarma forum, the specs for the two drivers are:
    Driver model #MW 6500
    Fs: 31.0000 Hz (Free air resonance)
    Vas: 2.6486 ft^3 (Compliance volume)
    Qts: 0.2190 Total Q
    Qms: 1.3000 Mechanical Q
    Qes: 0.2640 Electrical Q
    Sd: 0.0130 M^2 (Piston area)
    Xmax: 3.1800 mm (Cone excursion, linear)
    Revc: 6.5000 ohms (DC resistance)
    Znom: 8.0000 ohms (Nominal impedance)
    Pmax: 35.0000 watts maximum rated power

    Driver model #MW 6503
    Fs: 29.8600 Hz (Free air resonance)
    Vas: 3.0017 ft^3 (Compliance volume)
    Qts: 0.3100 Total Q
    Qms: 1.7680 Mechanical Q
    Qes: 0.3760 Electrical Q
    Sd: 0.0130 M^2 (Piston area)
    Xmax: 3.1800 mm (Cone excursion, linear)
    Revc: 6.5400 ohms (DC resistance)
    Znom: 8.0000 ohms (Nominal impedance)
    Pmax: 35.0000 watts maximum rated power

    It appears that the Q's and compliance of the two drivers are quite different. Will this make an audible difference in their performance? Will I need to replace the working driver as well (ending up with unmatched woofers as well as unmatched tweeters)?
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  • billinrio
    billinrio Posts: 8
    edited November 2009
    I have discovered after submitting my original posting that the problem is not the crossovers of my Monitor 7B speakers. Rather, both of the woofers have issues. One of them is "frozen", with no displacement whatsoever of the cone. The other has developed a tear in the butyl surround. I have written to Polk CS and am awaiting their response. I suspect that they don't have any more of the MW6500 drivers. If another, such as the MW6503 is available, I wonder if that option would require modification of the crossovers.
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  • Face
    Face Posts: 14,340
    edited November 2009
    Frozen drivers are often the result of a speaker that was dropped or mishandled.
    "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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  • ANWKLO
    ANWKLO Posts: 173
    edited November 2009
    billinrio wrote: »
    I have discovered after submitting my original posting that the problem is not the crossovers of my Monitor 7B speakers. Rather, both of the woofers have issues. One of them is "frozen", with no displacement whatsoever of the cone. The other has developed a tear in the butyl surround. I have written to Polk CS and am awaiting their response. I suspect that they don't have any more of the MW6500 drivers. If another, such as the MW6503 is available, I wonder if that option would require modification of the crossovers.

    My Monitor 5's MW6500 were replaced by MW6502. I can't hear the difference.:)
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  • skrol
    skrol Posts: 3,393
    edited November 2009
    Polk CS told me that the MW6500 and MW6503 are 8 ohm (6.5 ohm stated above) and the MW6502 is a 4 ohm. Is this true?
    Stan

    Main 2ch:
    Polk LSi15 (DB840 upgrade), Parasound: P/LD-1100, HCA-1000A; Denon: DVD-2910, DRM-800A; Benchmark DAC1, Monster HTS3600-MKII, Grado SR-225i; Technics SL-J2, Parasound PPH-100.

    HT:
    Marantz SR7010, Polk: RTA11TL (RDO198-1, XO and Damping Upgrades), S4, CS250, PSW110 , Marantz UD5005, Pioneer PL-530, Panasonic TC-P42S60

    Other stuff:
    Denon: DRA-835R, AVR-888, DCD-660, DRM-700A, DRR-780; Polk: S8, Monitor 5A, 5B, TSi100, RM7, PSW10 (DXi104 upgrade); Pioneer: CT-6R; Onkyo CP-1046F; Ortofon OM5E, Marantz: PM5004, CD5004, CDR-615; Parasound C/PT-600, HCA-800ii, Sony CDP-650ESD, Technics SA 5070, B&W DM601
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  • ANWKLO
    ANWKLO Posts: 173
    edited November 2009
    skrol wrote: »
    Polk CS told me that the MW6500 and MW6503 are 8 ohm (6.5 ohm stated above) and the MW6502 is a 4 ohm. Is this true?

    Not sure the data is correct:confused:

    http://www.audiokarma.org/forums/showthread.php?t=65109&highlight=mw6500+mw6502
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