Upgrading my 1981 Monitor 7 Speakers?

Hi,
This is my first time posting to this forum. Briefly, I am the original owner of a pair of Polk Monitor 7 speakers bought in 1981, and carefully attended to ever since. They are in excellent physical condition, albeit the tweeter and woofers have a few particles of lint stuck to their surfaces, but otherwise they're in fine shape.

I have always enjoyed listening to music (mainly jazz) through these speakers that are powered by my Conrad Johnson SA250 amp and SC26 preamp, but wonder if it may be time to upgrade the Polks. After all, the capacitors in their crossover circuits are nearly 4 decades old. I do a lot of hobby electronics, so I'm confident that I could do a change out to new caps and resistors if needed, but my question to you is will the new components improve the sound quality? I am particularly curious to know if I can do anything to improve bass response (i.e., some call this bass tightness) and sonic separation.

I appreciate your thoughts on this or other upgrades to my Monitor 7s, and thank you for your time.

Bob

Comments

  • pitdogg2pitdogg2 Posts: 14,715
    It sure wouldn't hurt as they are way past their prime. Sonicaps and Vishay-mills resistors are favored by quite a few here. Clarity caps are also a good choice. Most will replace their 5watt resistors with a 10 or 12 watt version keeping the original ohm value. you may need to get creative as the film caps will be much larger than the old NP electrolytic
  • Thanks. I googled and found the home pages for both Sonicaps and Vishay-mills. Is there a central supplier (US) that carries both? It would be more convenient, but not a major issue. Second question: I believe the crossovers in this speaker has both mylar and electrolytic caps; true? If so, does anyone have recommendations for the mylar cap, or is it good despite its age? My understanding is that mylars are not as prone to aging as are electrolytics. Please correct me if I've got anything wrong here.

    Thanks again,

    Bob
  • F1nutF1nut Posts: 42,966
    edited May 18
    Here's what can and should be done.

    https://forum.polkaudio.com/discussion/180294/fs-monitor-7bs-upgraded-with-extras

    FYI, that should read "resistor value adjusted."
    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

  • proteusmaximusproteusmaximus Posts: 22
    edited May 18
    F1nut wrote: »
    Here's what can and should be done.

    https://forum.polkaudio.com/discussion/180294/fs-monitor-7bs-upgraded-with-extras

    FYI, that should read "resistor value adjusted."

    Your upgrade is very impressive. Have you posted more details on your upgrade? (I'll search in the forum to see, but please let me know urls if you don't mind.) Also, I'm not following "resistor value adjusted"; did you remove the fuse and replace it with a resistor? I apologize for my confusion, but it's my default setting.

  • F1nutF1nut Posts: 42,966
    The resistor has a value of .5 ohm, which needs to be compensated for when removed. Note, I removed everything to do with the fuse as the wires connected to the fuse holder were heavily oxidized, which will affect their ability to carry the signal.

    Study the pictures, which are worth a thousand words.
    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

  • A final question: For both caps and resistors, is there any value in spending the extra money to get matched pairs? The cost isn't too much, but I am curious to know.
  • cincycat13cincycat13 Posts: 860
    e92cgtf7npqd.png

    It's not much more but not how I would spend my money. My opinion is it's only important if you are mounting capacitors in parallel to get a final value. And even then they just have to be close in value to prevent one of them from acting as a bypass capacitor. I don't see a need to create values for the 7b schematic.
  • Thanks cincycat13. I will open up one of my 7Bs later this morning to confirm its crossover components, and will order upgrades thereafter. I'd like to get the new components in and tested before the end of the month; I'm quite excited to see if I will be able to hear a difference.
  • My 7Bs' SNs are 7b-43852 and 7B-43861. Here's what my crossover contains. I assume my crossover is the same as other 7Bs. Let me know if there's something I'm missing. wpfp5467o9rp.jpg
  • My 7Bs' SNs are 7b-43852 and 7B-43861. Here's what my crossover contains. I assume my crossover is the same as other 7Bs. Let me know if there's something I'm missing. wpfp5467o9rp.jpg
  • cincycat13cincycat13 Posts: 860
    edited May 19
    glzcb7g48d04.png

    There at least 3 versions of m7 crossovers. With the 2.7 ohm i would guess yours are closer to this. You can search the sticky thread.

    Do you have the sl2500 tweeter or the peerless?
  • Peerless. I think the last schematic posted is for later versions; the first one looks right to me. (Sorry about duplicate posts with the photo. I don't know how that happened.)
  • tonyp063tonyp063 Posts: 686
    Take a look at this.
    https://forum.polkaudio.com/discussion/180627/7a-crossover-question-difference

    Schematic is there & it's correct.
    PM me if you would care for a copy of the BOM I used
  • I just ordered two of the following: Gen I Sonicap 12 uF cap, Gen I Sonicap 34 uF cap, 2.7 ohm vishay mills resistor, and 4.5 ohm Vishay Mills resistor.
  • FaustinFaustin Posts: 896
    I just ordered two of the following: Gen I Sonicap 12 uF cap, Gen I Sonicap 34 uF cap, 2.7 ohm vishay mills resistor, and 4.5 ohm Vishay Mills resistor.

    You are all set. May want to check the fuse connection and associated wiring as they corrode over time. Ask F1nut. He has been there. And consider new cabinet wire and as long as you are at it, new gold plated copper binding posts. It will all be worth it. 7's are a very nice speaker.
  • F1nutF1nut Posts: 42,966
    edited May 20
    Monitor 7 fuse holder/wires.

    rxcq1pm1cpja.jpg

    I need to correct one thing though, the fuse measured .2 ohms, not .5 ohms. I used a 4.7 ohm instead of the stock 4.5 ohm to compensate. Yes, .2 ohms is quite audible.
    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

  • Faustin wrote: »
    I just ordered two of the following: Gen I Sonicap 12 uF cap, Gen I Sonicap 34 uF cap, 2.7 ohm vishay mills resistor, and 4.5 ohm Vishay Mills resistor.

    You are all set. May want to check the fuse connection and associated wiring as they corrode over time. Ask F1nut. He has been there. And consider new cabinet wire and as long as you are at it, new gold plated copper binding posts. It will all be worth it. 7's are a very nice speaker.

    Will do. Anyone have any opinions on using braided v copper wires, if I chose to replace corroded ones?

  • FaustinFaustin Posts: 896
    I think using 14 or 16 gauge stranded copper wire would be the way to go. Perhaps some others will chime in.
  • I installed the new caps and resistors, and replaced fuse wires. No issues, and my speakers sound great. Q: Is there a 'burn-in' period, and if so, how long? Thanks to all your responses. They were extremely helpful.
    Bob
  • pitdogg2pitdogg2 Posts: 14,715
    Yes it takes about 100 hours. Most of us just let them play radio while at work or gone. I let mine play 24/7 for about a week.
  • pitdogg2 wrote: »
    Yes it takes about 100 hours. Most of us just let them play radio while at work or gone. I let mine play 24/7 for about a week.

    Good to know, thanks.
  • FaustinFaustin Posts: 896
    pitdogg2 wrote: »
    Yes it takes about 100 hours. Most of us just let them play radio while at work or gone. I let mine play 24/7 for about a week.

    ^^^^^^^^^^^ This
  • I'm extremely pleased with the resulting improvement in my speakers following upgrading their crossovers! I don't recall them ever sounding so good: bass is much tighter and defined, with greater sonic clarity overall. Many thanks for everyone's help. - Bob
  • dromundsdromunds Posts: 8,334
    Outstanding. I am a big fan of those speakers. Keep posting, this is a good bunch of folks.
  • It's been 6 months since I upgraded my 7s, and I am so very happy with the result. Along the way I switched out my CJ preamp for a new PS Audio BHK sig preamp and Direct Stream DAC. Also subscribed to Qobuz; great streaming service! Sound is more than I could ever have anticipated and simply the best I've heard from my Polks. I'm a happy camper.
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