SDA-2 crossover upgrades, totally confused

nspindel
nspindel Posts: 5,343
edited March 2008 in Vintage Speakers
I've been reading several threads about upgrading the crossovers in the SDA-2's. Particularly:

http://www.polkaudio.com/forums/showthread.php?t=28024

and

http://www.polkaudio.com/forums/showthread.php?t=34333

Just when I thought I was ready to start ordering the parts, my speakers threw me for a loop. I apparently have very different SDA-2's. According to the date stamped on the drivers, mine are from 1988. Left serial number is 20717 and Right serial number is 19869. I'm noticing that the title of the first thread I'm referencing is "1st generation SDA 2 crossover upgrade guide." Perhaps there is a 2nd generation SDA 2, but I can't find any obvious posts about this.

First of all, these only have one tweeter, one main driver, and one dimensional driver (plus the passive radiator of course).

Second, I appear to have a completely different crossover circuit than those described in the above SDA-2 threads. I only have one crossover board, feeding all three drivers, mounted on a coil just below the connection posts. This looks like a much simpler circuit than those described in the above threads. I don't even see a resistor on the board. Also, the wires to feed the drivers have distinct quick-connects, so no need to even label any wires.

Pictures of the crossover inside the cabinet and pulled out are provided, along with the front of one of the speakers as well as the rear label of one.

I'm wondering what my upgrade options are for this crossover? It would seem from the simplicity of the design that it's likely a lot cheaper than the dual crossover design, and simpler to do. Any advice, even a point to another thread dealing with this topic (I've searched, but nothing is jumping out at me) would be most appreciated.

Thanks....
Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • MillerLiteScott
    MillerLiteScott Posts: 2,561
    edited January 2008
    They look like Studio 2B's but should be the same as any SDA 2B. I have a pair of modified 2B's using a 4.1tl upgrade. If you search in the vintage section I think there is a couple of threads and links about these mods.

    I think I spent @ $ 350.00 for Sonicaps and RDO 198 tweeters for the 4.1tl upgrade. Well worth it compared to what is out there today probably by a factor of 10.

    I am not an expert on this but I modded a pair. Others will chime in.

    Scott
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D
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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    I should note that I've already done the silk tweeter upgrade, I'm definitely a believer there.

    So if these are 2B's, wouldn't the label on the back actually say "2B"? I guess not...
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • Face
    Face Posts: 14,340
    edited January 2008
    Read the values of the caps and resistors and replace with better parts of the same value.
    "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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  • F1nut
    F1nut Posts: 50,494
    edited January 2008
    So if these are 2B's, wouldn't the label on the back actually say "2B"? I guess not...

    The sticker on your crossover board clearly says SDA 2B. Yours are the "Studio" version.

    Your options are to leave them alone, upgrade the caps and resistors using the stock specs or upgrade to the "TL" specs. IMO, upgrading to the "TL" specs results in a nicer sounding speaker, but since you already have the RD0194-1 tweeters you may just want to upgrade to the stock specs as you'll have to replace the RD0194-1's with RD0198-1's.
    Political Correctness'.........defined

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    President of Club Polk

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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    Thanks F1nut - bit silly of me not to see the 2B marking on the board. I was just going by the back of the cabinet.

    So from the looks of it, if I stick with the stock design and the 194 tweeters, I would just need to replace the 12uF and 20uF caps. Even with Sonicaps, that's less than a hundred bucks for both speakers.

    I was checking out Scott's thread:

    http://www.polkaudio.com/forums/showthread.php?t=57691

    I'm wondering what the 30uF cap is? DarqueNight's post #9 in that thread says that the only thing needed for the RD0198 upgrade would be the 5.8uF cap in parallel with a 2.7ohm resistor. Would I need that 30uF cap in there as well? Because my board has nothing there right now.

    Also, Scott - your picture in the beginning of that thread shows 5 caps per board, including a 10uF. What's that cap for? I don't see it in your final board.

    I suppose the smart thing would be to just replace the 12's and the 20's and check out how the 194's sound at that point. But I've not always done things the smart way - there's always the option of selling the 194's and buying the 198's and doing the full upgrade...

    Thanks again for all the help.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • MillerLiteScott
    MillerLiteScott Posts: 2,561
    edited January 2008
    The 10uF is added to the 30uF to come up to 40uF and it is mounted on the back of the crossover due to the limited space on the PCB. The Sonicaps are much larger than the original caps.

    Enjoy,

    Scott
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D
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  • F1nut
    F1nut Posts: 50,494
    edited January 2008
    Each crossover for your speakers has one of the following, 12uF, 20uF, 40uF caps. One 2.7 ohm resistor, one 750pF silver mica bypass cap and one polyswitch.

    To do the stock spec upgrade you'll need the following Sonicaps.

    (1) 12uF
    (1) 20uF
    (1) 10uF
    (1) 30uF (Connect the 30 and the 10 in parallel to obtain 40uF. The 30 has to be mounted vertically and the 10 has to be mounted under the board)

    (1) 2.7 ohm Mills resistor

    Remove and do not replace the 750pF silver mica.

    Remove the polyswitch and replace with a jumper (S1) IF you have a quality amp. Otherwise, replace the poly with a new one.

    To do the "TL" upgrade do as above adding a 5.8uF Sonicap (custom value) in the C5 position, running the one lead into the H hole and the other lead into the C5 hole closest to R2. Replace tweeters with RD0198-1.
    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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  • Ricardo
    Ricardo Posts: 10,636
    edited January 2008
    nspindel wrote: »
    So from the looks of it, if I stick with the stock design and the 194 tweeters, I would just need to replace the 12uF and 20uF caps. Even with Sonicaps, that's less than a hundred bucks for both speakers.

    That, plus:
    -Change the resistor you have in each crossover; use Mills.
    -Change the polyswitches (little blue thingy; this is a tweeter protection that you can get free by calling Polk CS; you'll probably get yellow this time).
    -Remove the Silver Mica by-pass; that's the brownish little thing that's right beside the yellow cap.

    You'll have speakers for the next 20 years.
    _________________________________________________
    ***\\\\\........................... My Audio Journey ............................./////***

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    Thank God for different opinions. Imagine the world if we all wanted the same woman
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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    MillerLiteScott wrote: »
    The 10uF is added to the 30uF to come up to 40uF and it is mounted on the back of the crossover due to the limited space on the PCB. The Sonicaps are much larger than the original caps.

    Enjoy,

    Scott

    Ah, now I get it. In the picture I posted you couldn't see that cap behind the coil. I just pulled the passive radiator off and I see what you what you did now. So it's not as simple as just trying out a $100 upgrade. Those 30's are where most of the expense is...
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    Not to be overly repetitive, but thanks again for all the help!

    When I pull the bypass cap, do I need to add a jumper or should I just leave it empty?

    I'm fairly confident that I can just pull the polyswitch, I'm using an NAD2200 in a relatively small room, so the volume never goes up too high - I've never tripped the polyswitch since I got this amp, that's for sure.

    I think my only remaining question is, where the heck is the 2.7ohm resistor? Unless it's underneath something else, I just don't see it.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • Ricardo
    Ricardo Posts: 10,636
    edited January 2008
    -You do not need a jumper in place of the bypass cap
    -The resistor is that light brown "ceramic like" component that is beside C5
    _________________________________________________
    ***\\\\\........................... My Audio Journey ............................./////***

    2008 & 2010 Football Pool WINNER
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    Thank God for different opinions. Imagine the world if we all wanted the same woman
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  • F1nut
    F1nut Posts: 50,494
    edited January 2008
    It's the off white ceramic block between the B and G holes.
    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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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    Ah, I was looking for the smaller, round kind. Thanks!

    I'm assuming I'll need to extend the top lead on the vertically mounted 30uF. Any specific product I should use there, or just rig something with a piece of wire? Same question on the jumper when I pull the polyswitch, do I just use a piece of copper or is something made to fit the bill?
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • geoff727
    geoff727 Posts: 546
    edited January 2008
    nspindel wrote: »
    I don't even see a resistor on the board.

    It's the small, tan-colored, rectangular-shaped box. Replace with a Mills 12W resistor of the same ohm rating.

    Replace the capacitors with the good Sonicaps (one 12 uf, one 20uf, and 2x20uf to make a 40uf per crossover board). Consider replacing the 750pf capacitor with a good Sonicap Gen II or Platinum series .1uf cap. Some people like to do this; others don't. It's just a matter of preference in the brightness of the top end. Solder it with Cardas Quad-Eutectic solder and you'll be in business.

    And post pics when you're done! Good luck!

    P.S. This would be a non-"TL"-type upgrade, since you already have the RD0194's.
    Polk SDA SRS 2
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    Polk Lsi9
    Infinity RS-II (modded)
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    System: http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1290711373
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  • F1nut
    F1nut Posts: 50,494
    edited January 2008
    nspindel wrote: »
    I'm assuming I'll need to extend the top lead on the vertically mounted 30uF. Any specific product I should use there, or just rig something with a piece of wire? Same question on the jumper when I pull the polyswitch, do I just use a piece of copper or is something made to fit the bill?

    Correct on both. Grab some 18 or 20 gauge solid core copper wire at Rat Shack and you're set.

    I highly recommend going with the 30 and the 10 as mounting a 20 under the board becomes an issue. A bypass cap is no longer needed as the replacement caps are high quality. I tried it with both the Sonicap Gen II and Platinum series .1uf cap. The result was artifacts which sound un-natural, but it's up to you. Waste of money, IMO.
    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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  • MillerLiteScott
    MillerLiteScott Posts: 2,561
    edited January 2008
    nspindel wrote: »
    Ah, I was looking for the smaller, round kind. Thanks!

    I'm assuming I'll need to extend the top lead on the vertically mounted 30uF. Any specific product I should use there, or just rig something with a piece of wire? Same question on the jumper when I pull the polyswitch, do I just use a piece of copper or is something made to fit the bill?

    You have to use a small piece of wire IIRC F1 and I used some 16 guage copper wire but you can use whatever you like. We also use the extra length cut from the new caps to make the polyswitch jumper.

    Scott
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D
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  • F1nut
    F1nut Posts: 50,494
    edited January 2008
    Was it 16 gauge? I stand corrected, too much wire around here.
    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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  • MillerLiteScott
    MillerLiteScott Posts: 2,561
    edited January 2008
    I think you are right it was 18 guage. Sorry my wife was talking to me when I was typing.

    Scott
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D
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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    This should be fun, I'm looking forward to this. I haven't done any electronics work in 20 years, but it should be just like riding a bike. One lesson I learned the hard way 20 years ago - always use a heat sink!!!!

    I got my first sda's on my 21st birthday. Those were the crs+'s, which I had until 3 years ago when I basically did a costless upgrade to the 2B's. I've gone through lots of equipment over the years, but I've not been without a pair of sda's for 19 years - I'm excited to hear what the upgraded version sounds like!

    As long as I'm doing all this, I might as well sell the 194's and go to the 198's. The 194's are practically brand new, I don't think there's more than 25 hours on them.

    I'll definitely pop some pictures up when I'm done.

    Thanks again all....
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • danger boy
    danger boy Posts: 15,722
    edited January 2008
    nspindel wrote: »
    I should note that I've already done the silk tweeter upgrade, I'm definitely a believer there.

    So if these are 2B's, wouldn't the label on the back actually say "2B"? I guess not...

    nope! 2's, 2A's and 2B's will all three only say SDA 2
    PolkFest 2012, who's going>?
    Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin:
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  • schwarcw
    schwarcw Posts: 7,335
    edited January 2008
    Good luck on your upgrade. Jesse, Ricardo and the others have given you some good advice. Keep us posted!
    Carl

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  • Disc Jockey
    Disc Jockey Posts: 1,013
    edited January 2008
    Have fun, the upgrade is well worth it. If you do decide to use the bypass caps, the short lead goes towards the driver.
    "The secret of happiness is freedom. The secret of freedom is courage." Thucydides
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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    From everything I've read, if I'm using Sonicaps then the bypass caps aren't really necessary, so I'm skipping those for now.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    Ordered from Soniccraft today. Nice folks! The 5.8uF is a custom cap, they've got a 5.6 but I wanted to stick to spec. "Sorry, but since you ordered a custom size, we won't be able to ship until tomorrow." Oh, awright.... Very cool service!

    And by virtue of me ordering the 5.8uF, I'm obviously going all out and replacing the practically-brand-new replacement tweeters. If I'm going to do it, do it right. So look for my 194's to show up on the FS thread.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    Should also note that I'm also following DarqueNight's lead from his CRS+ upgrade thread and replacing the binding posts with the Cardas CCGR-S's.
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • heiney9
    heiney9 Posts: 25,165
    edited January 2008
    nspindel wrote: »
    Should also note that I'm also following DarqueNight's lead from his CRS+ upgrade thread and replacing the binding posts with the Cardas CCGR-S's.

    Have fun, take your time, do one at a time and you will be amazed at the improvements. They must break in for about 200 hours before they will start to transform :) Just keep that part in mind when you first fire them up.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
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  • MillerLiteScott
    MillerLiteScott Posts: 2,561
    edited January 2008
    Mine took a bit longer to come around. Probably double that.

    Sounds like we are going to be up to 3 pairs of 2B tl's in the world now, as far as I know.

    Scott
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D
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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    MillerLiteScott wrote: »
    Mine took a bit longer to come around. Probably double that.

    Sounds like we are going to be up to 3 pairs of 2B tl's in the world now, as far as I know.

    Scott

    Wow, are there only that few??? I feel special :)
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    heiney9 wrote: »
    Have fun, take your time, do one at a time and you will be amazed at the improvements. They must break in for about 200 hours before they will start to transform :) Just keep that part in mind when you first fire them up.

    H9

    Here's a question - does it matter with electronics what source material you're using for the burn in? I know when I burned in headphones, I used the Alan Parsons studio reference cd, with all kinds of sin waves, reference tones, pink noise, music, various types of sounds, etc. That worked out very well, but this was done for purposes of loosening up the drivers. Is there any particular type of source that works "better" for electronics, or better yet, faster?
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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  • nspindel
    nspindel Posts: 5,343
    edited January 2008
    Also, what kind of volume do I need to push for the burn in? heiney9 says 200 hours, MillerLiteScott says 400 - 400 hours is over 2 weeks! If I need this turned up at any sort of real volume for that long, my wife's going to KILL me. Breaking in headphones was a lot quieter of course....
    Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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