polk sda 2a crossover upgrade + tl mod questions

JonathanPeterson
JonathanPeterson Posts: 103
in Vintage Speakers
looking to redo cross overs on sda 2a

ordering everything from partxconnexion. here is the parts list

4 of Solen Capacitor 130uF 400Vdc PB SeriesSOLEN-51571
4 of Solen Capacitor 20uF 400Vdc PB SeriesSOLEN-51558
4 of Mills Resistor 2R7 Ohm 12W MRA-12 SeriesMILLS-71906

2 of ClarityCap Capacitor 12uF 250Vdc CSA SeriesCLARITY-81528

tl mod part:
2 of ClarityCap Capacitor 5.6uF 250Vdc CSA SeriesCLARITY-81525
5.8uF is not available from clarity cap but most people here said its fine to use 5.6

question is if i remove polyswitch and replace it with .5ohm resistor, which is not available, does this resistor modulate rdo 198 tweeter brightness? i was thinking making a little switch and using .39 ohm, .47ohm and .56ohm resistors to switch between the 3 values to modulate tweeter brightness. is the difference between resistors sufficient to notice tweeter brightness? problem is partconnexion doesnt have .5ohm mills resistor.

or should i just leave polyswitch on?
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  • Unknown
    Unknown
    edited November 2021
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  • F1nut
    F1nut Posts: 51,880
    I wouldn't use Solen for anything but the 120uF shunt. You could get eight of 10uF CSA for the 20uF. Of course, you could order the 20uF, 12uF and 5.8uF in the exact values from Sonicap.

    Mills 0.5 ohm
    https://www.partsconnexion.com/MILLS-71899.html

    You could ask PC to source two 5.6uF that measure closer to 5.8uF.

    Making a resistor L pad (switch) is not a good idea, just more crap in the signal path. Besides, the 0.5 ohm is proven.

    Yep, get rid of the 750pF.

    Do you have the RD0198 tweeters already?
    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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  • Unknown
    Unknown
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  • invalid
    invalid Posts: 1,497
    edited November 2021
    I did my 2A's exactly the way F1nut describes. If you add a switch it will have a negative effect on the sound. The sonicaps aren't as bright as the clarity caps. I ordered 5.6uf caps that measured closer to 5.7uf.
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  • pitdogg2
    pitdogg2 Posts: 27,155
    JonathanPeterson wrote: »

    To reveal the actual build completely it's sda 2a cross overs rdo-198 tweeter and 4 dynaudio 17w75xl 4ohm drivers

    Basically I am replacing each 8ohm 6510 driver with 2 17w75xl 4ohm drivers in series.

    Everything will be in a sealed box without passive radiators.

    OH Boy, Where Do I Start?



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  • pitdogg2
    pitdogg2 Posts: 27,155
    Dynaudio makes good stuff. I was not aware you could still buy drivers. I know I had bought and sold Dynaudio mids and tweeters yrs ago.
    You however should just build new speakers.
    It's been my experience that once you rebuild new crossovers with supreme caps and resistors the speaker no longer have the flaws that you speak of. What you hear are the "cost" effective product Polk put out. When Polk saved .70 per speaker you and I do not see that translates to hundreds of thousands of dollars in actual savings across the board for Polk.

    To now build with different drivers and no longer use the passive for the low end I cannot see how that will make a better speaker. Yes the SDA2a is very expensive to recap because of the huge shunt cap required. Solen caps just kill my ears to no end. For the shunt I used the Axon cap and Sonicaps everywhere else. It made a huge difference in how they played and another Polkie is enjoying them as we speak.
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  • F1nut
    F1nut Posts: 51,880
    You owe me 5 minutes for wasting my time.
    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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  • Unknown
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  • pitdogg2
    pitdogg2 Posts: 27,155
    JonathanPeterson wrote: »
    So better to get 6 axon 43uf capacitors instead of 2 130uf solen?

    https://www.partsconnexion.com/AXON-73688.html

    I can always go back to original 2a. It's more of an experiment. Not butchery

    I got 8 17w75xl for free. Actually made 200$ from selling the huge speaker box they were used in.

    Red rose audio or something. Only left speaker with all tweeters missing and cross overs missing.

    Do what you need to it's cheaper for 1 big Solen either way you'll need to put them off to the side and run wires to the XO. Both are too big to hang off the stand up on the binder cup.

    I went with 6 Axon.
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  • invalid
    invalid Posts: 1,497
    Don't butcher them by trying to redesign them
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  • Clipdat
    Clipdat Posts: 13,098
    pitdogg2 wrote: »
    You however should just build new speakers.

    QFT.
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  • Clipdat
    Clipdat Posts: 13,098
    You come asking for advice, but then you ignore it. Strange.

    Since you are insisting on using non-Polk drivers and are essentially "rebuilding" the speaker from the ground up into a grotesque Frankenstein's monster, then you might as well just save a buck and use Dayton caps all around because it won't make any difference whatsoever at this point.
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  • xschop
    xschop Posts: 5,267
    edited November 2021
    If you don't like the hybridized bass, you could try porting them? At least you're not trying to incorporate titanium tweets.
    JonathanPeterson wrote: »

    There is this smear or absence in upper midrange in sda that dynaudio drivers seem to resolve. Had sda-2b, crs+ with cross overs redone for many years

    From my recent experimenting, the 6510's don't articulate the midrange as nicely as their 6516 counterparts. The 6510's suspension spider is much more loose given the same construction and DCR as 6516's with tighter suspension.
    Post edited by xschop on
    Don't take experimental gene therapies from known eugenicists.
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  • Unknown
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  • invalid
    invalid Posts: 1,497
    Why don't you just get a different speaker instead of putting all that money into these.
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  • Gardenstater
    Gardenstater Posts: 4,785
    edited November 2021
    My 2c is that I would do all the mods I could to my Polks to let them be all they can be, FIRST. Blackhole5 behind drivers, anti-diffraction wool on the baffle, anti-diffraction frame on cabinet edges, armacell inside spokes of stamped steel baskets, phase plugs, Rob's rings to stiffen baffle, anti-vibration speaker stands..... Only then will you hear how beautiful the midrange can sound.

    I'm all for experimentation though so carry on and report. :)
    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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  • invalid
    invalid Posts: 1,497
    There is this smear or absence in upper midrange in sda that dynaudio drivers seem to resolve. Had sda-2b, crs+ with cross overs redone for many years and about 12-15 pairs of other 1000-5000$ speakers.



    That smear you are talking about is taken care of with the sonicap capacitors and the black hole 5 that you install behind the driver's. What amp are you using to drive these?
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  • Gardenstater
    Gardenstater Posts: 4,785
    What Thiele Small Parameters do you have for the MW6510? This is all I have been able to find so far:

    xp08x55wbzz2.jpg


    Is this the driver you have? http://www.dynaudioacoustics.cn/down/DYNAUDIO_17W75v2.pdf
    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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  • Unknown
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    edited November 2021
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  • Gardenstater
    Gardenstater Posts: 4,785
    edited November 2021
    Well OK. It seems like the Qm is closer than in the non XL, but still not all that close, Compliance is unknown, DCR of two in series is close, Fs is different, BL is less. We can't really know much else can we? How do you know about sensitivity?

    Looks like they used the same voice coil as non XL but changed the magnet motor to a stronger one. Without having the compliance figures for the dynaudio the comparison is tough to make to the 6510.

    How are you going to get any bass without a passive radiator when the freq. response shown doesn't go much below something like 50 to 60 Hz?

    PS: Great website by the way, thanks!
    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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  • invalid
    invalid Posts: 1,497
    Try a real amp, no receiver will do the 2a's any justice.
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  • pitdogg2
    pitdogg2 Posts: 27,155
    invalid wrote: »
    Try a real amp, no receiver will do the 2a's any justice.

    Agree they play at about 3ohm.
    Parts Express basic film cap (Dayton) is made by Erse. So yea I can understand your thought that they didn't sound all that good, the caps were and will be the strangulations point if you keep using "cheap" capacitors.

    Much better cheaper caps out there. Even low rung Clarity caps (PX-CSA) are leaps better.
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  • Gardenstater
    Gardenstater Posts: 4,785
    edited November 2021
    JonathanPeterson wrote: »
    Sensitivity is around 88-89db just eye balling from graphs
    Vas is 20L. Cms and vas are usually proportional. If Polk vas is 20L and 17w75xl is 20L then their cms are probably the same. I mounted dynaudio in 4 crs boxes and sealed passive radiators. Tweeter and woofers play pretty balanced. I dont want a ton of bass . I use 15" velodyne subwoofer..fsr-15(with parts Express 500w plate amp with dsp). Velodyne plate amps all blow 1 hour after warranty expiration date. Next to 2b Polks these polkdynaudiosteins sounded much more revieling, clean, open and forward smearless. Some voices and string instruments sound very recessed in 2b(crossovers redone using parts Express basic film capacitors. Nothing fancy like clarity)

    But where are you getting those values of sensitivity (from what graph?) and Vas (Compliance Volume) from for the MW6510, if the only info. you have is the chart that I posted above^^?

    I mean I understand that you are assuming Vas and Cms will be the same if the driver surface area is the same, but are they? It looks like the Polk is around 130cm^2 vs 120cm^2 for the Dynaudio, so Polk is 8.3% greater.

    https://mynewmicrophone.com/full-list-thiele-small-speaker-parameters-w-descriptions/#Vas:-Equivalent-Compliance-Volume
    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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