Monitor 7B schematics-XOVER upgrade.

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Toolfan66
Toolfan66 Posts: 17,051
edited November 2009 in Vintage Speakers
Looking for the schematics for the 7B's with MW6500 driver and Peerless tweeter.

I have 2 sets now and want to use one set for my first crossover upgrade.

any help in this project would be great.

Thanks.
Post edited by Toolfan66 on
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  • Face
    Face Posts: 14,340
    edited October 2009
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    Pull your crossovers and see what you have.
    "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
  • Toolfan66
    Toolfan66 Posts: 17,051
    edited October 2009
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    4.5 10%5W
    2.7 10%5W

    34uf

    T1
    E-0012-1
    Mexico ( i have no clue what this is telling me )
  • Face
    Face Posts: 14,340
    edited October 2009
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    It's a 12uf cap for the tweeter hombre'.
    "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
  • ben62670
    ben62670 Posts: 15,969
    edited October 2009
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    Answer your phone.
    BTW tag your it:)
    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
  • Toolfan66
    Toolfan66 Posts: 17,051
    edited October 2009
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    ben62670 wrote: »
    Answer your phone.
    BTW tag your it:)

    HAHA it's in my car BRB.
  • Bubinga99
    Bubinga99 Posts: 283
    edited October 2009
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    Face wrote: »
    Pull your crossovers and see what you have.

    The schematic doesn't always agree with what's installed. The schematics sometimes show non-standard values. On one of my pairs of 2.3TL's the schematic shows 8uF whereas 8.6uF is installed on the crossover board (a 4.2uF non-polarized electrolytic in parallel with a 4.4uF mylar). It measures at 9.1uF, 14% higher than the schematic, but within spec of the values stamped on the case.
  • Toolfan66
    Toolfan66 Posts: 17,051
    edited October 2009
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    Face wrote: »
    It's a 12uf cap for the tweeter hombre'.

    Thanks..
  • Toolfan66
    Toolfan66 Posts: 17,051
    edited October 2009
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    With what I have what kind of tolerence do you have on the Resistors and Caps?

    I am looking at the Clarity or Solen Caps. But I can't find a 34uf could I get away with a 33uf and could somebody help me find Resistors . I am thinking I can tie the 2 values together and just have 1 Resistor correct?
  • ben62670
    ben62670 Posts: 15,969
    edited October 2009
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    33uf is perfectly fine:)
    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
  • Toolfan66
    Toolfan66 Posts: 17,051
    edited October 2009
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    Thanks Ben, What about the resistors can I just get 1 that equals the same value of both?

    I am very excited about doing this.
  • NJPOLKER
    NJPOLKER Posts: 3,474
    edited October 2009
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    I don't think that will work or Polk would have gone that way. I'd buy Mills from Sonic Craft of the exact same value and be sure to mark the spots where the existing caps and resistors are soldered so you will not have a problem later.
  • Toolfan66
    Toolfan66 Posts: 17,051
    edited October 2009
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    NJPOLKER wrote: »
    I don't think that will work or Polk would have gone that way. I'd buy Mills from Sonic Craft of the exact same value and be sure to mark the spots where the existing caps and resistors are soldered so you will not have a problem later.

    Thanks thats what I needed to hear, I will order parts tomorrow.
  • Toolfan66
    Toolfan66 Posts: 17,051
    edited October 2009
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    Solen, Sonic or Clarity Caps? with Mills.

    Shopping has me wanting to do my RTiA9's as well, But my 1C's will come after i do these M7's. I am just using these as a learning curve before I dig into the 1C's.
  • zarrdoss
    zarrdoss Posts: 2,562
    edited October 2009
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    that sounds good. dont forget A.I.C. lol
  • Face
    Face Posts: 14,340
    edited October 2009
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    I would go with Sonic Caps since Peerless 7's are pretty laid back.
    "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
  • comfortablycurt
    comfortablycurt Posts: 6,745
    edited October 2009
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    I can't wait to hear how this turns out for you...I'm planning on modding the XO's in my Peerless 7A's sometime next year. I've been planning on going with the Sonicap/Mills combo.

    I'm also going to add Mortite, Dynamat Extreme, upgraded binding posts etc...I just can't decide whether I want to do all of the upgrades at once or do it in stages.
    The nirvana inducer-
    APC H10 Power Conditioner
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    PolkAudio LSi9's/PolkAudio SDA 2A's/PolkAudio Monitor 7A's
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  • Toolfan66
    Toolfan66 Posts: 17,051
    edited October 2009
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    Can I use 12w mills instead of 5w?


    Curt I will keep it updated for you on how things go and sound.
  • Conradicles
    Conradicles Posts: 6,063
    edited October 2009
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    12w is good. Larry, you will be very happy with the results. I used cheap Dayton caps on my 1C's and the sound is so much better on so many levels.
    On my 2B's, I'm going to try the Clarity Caps Face suggested for the highs.
  • Toolfan66
    Toolfan66 Posts: 17,051
    edited October 2009
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    12w is good. Larry, you will be very happy with the results. I used cheap Dayton caps on my 1C's and the sound is so much better on so many levels.
    On my 2B's, I'm going to try the Clarity Caps Face suggested for the highs.


    Thanks!! I was thinking of using Clarity Caps for my 1C's. I will be using Sonic Caps as Face suggested for these 7B's.


    Thanks for the Help..


    Larry.
  • NJPOLKER
    NJPOLKER Posts: 3,474
    edited October 2009
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    http://www.10audio.com/sonicap_oimp_multicap.htm

    I don't know if you ever read this but it is worth looking at.
    I am sure the Clarity Caps are great but you'll be hard pressed to beat the performance of the Sonic Caps.
  • Toolfan66
    Toolfan66 Posts: 17,051
    edited November 2009
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    Well I got them done today..

    Crossovers are easy to do guys for those of you that are not sure about digging into it. I also used dynamat and mortite on the drivers and passive's
    They sound great.:cool:

    Will post some pics later.
  • zarrdoss
    zarrdoss Posts: 2,562
    edited November 2009
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    Well I got them done today..

    Crossovers are easy to do guys for those of you that are not sure about digging into it. I also used dynamat and mortite on the drivers and passive's
    They sound great.:cool:

    Will post some pics later.

    I wondered where you went today, lol
  • Gym123
    Gym123 Posts: 14
    edited December 2023
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    One of my customers asked me to check out his 7B because it sounded bad- it really, really does. The low end is terrible with the OEM woofer but definitely better with a Peerless 6-1/2" that I have from a previous build. I removed the terminal cup yesterday and that made a drastic improvement, so my next step is to measure the caps and see how far they have drifted.

    I don't remember any Polk speaker that sounds this bad- was this one of the reasons for the crossover upgrades you guys did?

    What's the best woofer replacement, since the 6502 is history? Just buy another that (hopefully) is in good condition? I looked at the 'replacement' from Speaker Exchange and it's 2dB less sensitive.

    And, aren't the OEM woofers 4 Ohm? The Monitor 7b crossover diagram I found shows 8 Ohms. and a fuse, but these don't have the fuse.

    I'll post photos of everything later. c

    Thanks
  • xschop
    xschop Posts: 4,837
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    6502's are 4 ohm
    Don't take experimental gene therapies from known eugenicists.
  • SIHAB
    SIHAB Posts: 4,631
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    I would replace both woofers... one not so good usually.
    Speakers: Polk Lsim, ATC SCM19 v2, NHT SuperzeroSpeaker Cables: DH Labs, Transparent, Wireworld, Canare, Monster: Beer budget, Bose ears
  • Gardenstater
    Gardenstater Posts: 4,281
    edited December 2023
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    The Monitor 7B did not use the 6502, it used MW6500. I believe that is your problem, or one of the main ones. I don't think I've ever heard of any 7B that did not have a fuse though, so I'm wondering if maybe you have the 7C. What tweeters do you have? What is the date on the crossover? Oh and what do you mean by you removed the terminal cup? You mean you played the speaker with a hole in the back of it?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
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  • pitdogg2
    pitdogg2 Posts: 24,927
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    Good questions George, I was a bit confused with the terminal cup statement.
  • Gym123
    Gym123 Posts: 14
    edited December 2023
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    The Monitor 7B did not use the 6502, it used MW6500. I believe that is your problem, or one of the main ones. I don't think I've ever heard of any 7B that did not have a fuse though, so I'm wondering if maybe you have the 7C. What tweeters do you have? What is the date on the crossover? Oh and what do you mean by you removed the terminal cup? You mean you played the speaker with a hole in the back of it?

    Yes, I played it with a hole in the cabinet and I know better than to crank it under that condition. Speakers are frequently tested in free air and since the spider has separated from the voice coil, it wouldn't have damaged it, anyway.

    I haven't been looking for long, but I have seen a lot of conflicting info about the Monitor 7 and these were made in 1986, as shown in the photos and it's more important for me, to see the component values if they match than whether it has a fuse.

    I also used my LCR meter to measure the components out of circuit and for anyone who wants/needs the value of the smaller inductor, this one measured .17mH, 1.5 Ohms.

    I called Polk and tech support told me to contact Midwest Speakers for a replacement- I asked if they're new and she said they are.

    Woofer is MW-6502, 4 Ohm as seen on the label and as measured (DC resistance of 3.6 Ohm).
    Tweeter is SL-2000




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  • Gym123
    Gym123 Posts: 14
    edited December 2023
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    xschop wrote: »
    6502's are 4 ohm

    I didn't have the driver in front of me but as my later post shows, it is 4 Ohm.

    I just searched for crossover diagrams and it would seem that these are the 7C- the fuse was replaced by the polyswitch.
  • Gardenstater
    Gardenstater Posts: 4,281
    edited December 2023
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    Nice to see some measurements as lots of people (myself included) don't have an LCR meter. Hopefully the dates on the crossovers match fairly closely with the dates on your drivers because those drivers were only found in the 7C, which came out sometime in late 1984 and was superseded by the Monitor 7 Series II sometime in 1990 I believe.

    Having the speaker sound better with a huge gaping hole in the back is indicative of something seriously wrong lol. Shouldn't be any bass to speak of with that arrangement with a passive radiator speaker, for one thing, and the alignment is a melding of the T/S parameters with the enclosure volume. Did I miss where you said that the spider was separated from the voice coil in your original comment? That would CERTAINLY mess things up badly. I had a crack in one of original MW6500s and that would occasionally cause some weird sounds with heavy bass material, but I can only imagine what a separated spider to VC joint would sound like. I hope you didn't test at high volume with the hole in the back, reducing the loading on the driver. These are pretty old drivers. You could try repairing with some Aleene's Tacky Glue and hope for the best.

    I don't know who sketched out that schematic for the 7B. The inductors should be 0.23mH, 22awg and 1.55mH, 18awg. Your schematic should be this one:

    https://us.v-cdn.net/5021930/uploads/attachments/4/6/7/2/8/18772.pdf

    se4oc000x345.jpg


    Post edited by Gardenstater on
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform