Monitor Series M10 And M10 Series 2? Do I have a mismatched set?

kjsnfl
kjsnfl Posts: 15
in Vintage Speakers
I picked this set up today for $50. They look to be in great shape. Looks like I have mis matched set. Does anyone know the difference?

One is an M10 the other is an M10 Series 2

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Comments

  • Gardenstater
    Gardenstater Posts: 4,459
    edited April 2022
    That's a strange one. They look the same from the front and both have the SL2500 tweeters. Those serial #'s are way far apart, besides one being a M10 (10B?) label and the other one a Series II label. Those crossovers would be very much different. I would have to look inside and make sure everything is the same. The schematics are here. Specifically I would want to make sure they are both like the 3rd schematic below. The 1st one is the 10B and the 2nd one is a tl mod (trilaminate mod) to the 10B:

    https://us.v-cdn.net/5021930/uploads/attachments/4/6/7/2/8/18776.pdf
    https://us.v-cdn.net/5021930/uploads/attachments/4/6/7/2/8/18777.pdf
    https://us.v-cdn.net/5021930/uploads/attachments/4/6/7/2/8/18778.pdf

    If you were to remove the passive radiators from both speakers you could probably take photos of the crossovers and post them up here, or simply remove the crossovers but that would entail dealing with the wiring leading to the drivers.
    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
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  • F1nut
    F1nut Posts: 50,537
    edited April 2022
    Both appear to be the Series 2.

    The left driver in the left speaker has either been removed for some reason and reinstalled or replaced because it is upside down.
    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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  • kjsnfl
    kjsnfl Posts: 15
    Thank you Gardenstater and F1nut ! I appreciate all the info. I didn't catch the speaker was upside down.

    I connected them to my Sansui AU-217 and I like them.

    The tweeter seems nice at low volumes, but breaks up a little at higher volumes. I bet there is an upgrade path for the tweeter and crossover. You guys recommend any upgrades or amp pairings?
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  • Gardenstater
    Gardenstater Posts: 4,459
    RDO-198 tweeter is the upgrade but I really think you need to check inside, to solve the mystery of the labels and serial #'s.

    It's possible that there may be ferrofluid (?) that is in need of replacement in those SL2500s but upgrading the tweeters would be the way to go.
    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
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  • kjsnfl
    kjsnfl Posts: 15
    I had to look inside, and something is up here. I started with the upside down driver which has the black Sharpe scribble on it. It has the same part number as the other drivers in the other speaker, but there are additional notes.

    It looks like the crossovers are slightly different.

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  • F1nut
    F1nut Posts: 50,537
    The drivers are all MW6503, so no worries there.

    The black marker...who knows, maybe the wrong date stamp.

    The crossovers are the same. The single big yellow mylar is a 12uF. Polk used two caps, a yellow and a blue to obtain the 12uF value for the other crossover. It's a common practice when one doesn't have the exact value on hand.
    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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  • kjsnfl
    kjsnfl Posts: 15
    Thanks for your time F1nut!

    This is great news, a matching pair (two years apart for some reason). They sound great to me. If you told me the didn't match in sound, I really couldn't tell.

    So do you recommend upgrading the tweeters and crossovers from your experience?
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  • Gardenstater
    Gardenstater Posts: 4,459
    I think the earlier mid 1990 speaker was in that transitionary period where they were still using up leftover parts from the 10B. Yes even labels!!! That's the way they flew lol. The other one is about a year later and is mid 1991 when they had used up all the 10B parts. That one MW6503 with the 1992 date was probably a replacement MW by a previous owner.

    That big yellow mylar capacitor had *better* be 16uF (not 12). I don't think that it is proper what they did in your newer speaker where they paralleled a mylar cap with a polarized electrolytic (?) for the tweeter. That electrolytic may be out of spec/past its prime and could possibly be responsible for the harshness you are hearing....who knows? Probably they should have used a mylar for the one paralleled with the 2.7 Ohm resistor as well but at least they did that with both of them.

    With your older transitionary PCB I believe I see where they jumpered out the polyswitch and also I see some concerning brown discoloration on the PCB around the 2.7 Ohm tweeter resistor which could be a sign of overheating.

    The tweeter inductors definitely look to be different sizes in the two crossovers so I have to wonder if they are the same DC resistances and inductances.

    Just my 2c.
    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
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  • kjsnfl
    kjsnfl Posts: 15
    Gardenstater, thank you! This is a fun dive. This is info I thought I'd never find!

    I like the idea of adding Mundorf or Jantzen caps. I noticed the brown stuff as well, maybe a new crossover would be nice.

    Do you like any specific brand or series of capacitors for this speaker?
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  • xschop
    xschop Posts: 5,000
    Old Polks are like Cracker Jacks, "A prize in every box".
    Don't take experimental gene therapies from known eugenicists.
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  • kjsnfl
    kjsnfl Posts: 15
    I see that now. If the stickers didn't match I don't know if I would have looked inside.

    Now I think it's required.
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  • Gardenstater
    Gardenstater Posts: 4,459
    edited April 2022
    kjsnfl wrote: »
    Gardenstater, thank you! This is a fun dive. This is info I thought I'd never find!

    I like the idea of adding Mundorf or Jantzen caps. I noticed the brown stuff as well, maybe a new crossover would be nice.

    Do you like any specific brand or series of capacitors for this speaker?

    I think those 2 brands are supposed to be fantastic but pretty darn expensive. I only have experience (great) with the Sonicaps but they have gotten pretty pricey. I'd check out the prices on those ones you mentioned but I'd seriously consider Claritycap CSA. I'd also check out all the corresponding inductors and make sure that the DCR is the same or close, even if I didn't have an inductance meter (I don't).

    In the 10B for the MW inductor they had a 1.55mH and they went to 1.75mH, 18awg for the Series 2 so I would *hope* that is what you have in both speakers. They also went from 0.4mH in the tweeter inductor to 0.22mH, 22awg in the Series 2.
    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
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  • pitdogg2
    pitdogg2 Posts: 25,436
    edited April 2022
    I don't think that it is proper what they did in your newer speaker where they paralleled a mylar cap with a polarized electrolytic (?)
    It happened more often that you realize. My 2.3tl crossovers were night and day difference between left and right. Yes they even did the same mylar and electrolytic paralleled together.

    Sonicap is a great cap and they have the exact cap values verses others which can be slightly off in value BUT still within tolerance. I've used Sonicaps in all my Polk builds and have not once regretted their use.
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  • kjsnfl
    kjsnfl Posts: 15
    Thanks for all the comments and advice. It's funny to hear about these things. I bet people don't ever open their speakers.

    I like the thought of Clarity Caps and Sonicaps. Both seem reasonably priced with good reviews.
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  • pitdogg2
    pitdogg2 Posts: 25,436
    kjsnfl wrote: »
    .
    I like the thought of Clarity Caps and Sonicaps. Both seem reasonably priced with good reviews.

    Yep

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