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  1. #1

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    Default SDA 1 crossover schematic

    I am the original owner of a pair of SDA 1's purchased in 1983. I would like to breathe some new life into these great old speakers. I have contacted Polk Service and they sent me schematic; however, it does not match the crossover in my speakers. My Polk SDA 1's are designated "Signature Edition". Each speaker has a gold colored metal plaquard placed centered below each pair of tweeters. Polk Service said they would look to see if they had information on the SDA 1 "Signature Edition". However, that was some time ago. Does anyone have the schematic for the "Signature Edition" SDA 1?

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    You don't really need a schematic. All the values are stamped on the components.
    'Political Correctness'.........defined

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    embo, Send us some photos, we need photos!
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    Default Pictures of SDA 1 Signature Edition

    Here are the pictures of my Signature Edition SDA 1s. This is the first time I uploaded pictures I hope it works.

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    Default Sigature Edition SDA 1s

    My pictures were too big and/or too many. I will post the images of the crossover in my next attempt
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  6. #6

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    Default Crossover of Signiture Edition SDA 1s

    As you can see there is a 2.5ohm 25W resistor in the stereo and dimensional array crossover instead of a 130uF capacitor. The larger inductor for the bass drivers is not pictured. I have yet to remove the crossover from the speakers to see how this is configured into the circuit.
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  7. #7

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    Default Inbetweeners

    Welcome to the forum. I would have responded to your question sooner, but I am just getting back from a week of vacation. I forwarded your schematic request to Ken Swauger in Polk's Customer Service department. He is the most knowledgeable about SDA's, particularly the very earliest and "transitional" models.

    I was not aware of an SDA 1 Signature Edition. The components in your crossover circuit pictures look very similar to the SDA 1A schematic, which I have attached below. I am thinking that the SDA 1 "Signature Edition" was one of those "transitional" SDA models and came between the SDA 1 and SDA 1A. I also assume that, in order to use up the remaining parts stock from the SDA 1, the SDA 1 "Signature Edition" was introduced in September of 1983. The SDA 1A came to market in 1984.

    I could not find any mention of an SDA 1 Signature Edition in my files. I do have a seven page document titled "Instructions For Updating Polk SDA-1 to SDA-1A" which mentions replacing the 130 uF capacitors with a 2.5 ohm 25 watt resistors. The following is taken from the "crossover modifications" section on pages 2 and 3 of the updating document:

    "STEP THREE - Removing Capacitors

    This step pertains to the two circuit boards mounted on two of the large coils on the crossover panel. Each of these circuit boards has attached to it a very large capacitor, one lead of which is soldered to one of the copper leads from the large coil on which the circuit board is mounted. The other lead is connected to the circuit board...This capacitor or capacitor assembly will be replaced by a 2.5 ohm 25 watt resistor, connected exactly as the capacitor is now connected."


    The task of modifying your crossovers has been simplified by Polk's deletion of the 130 uF capacitor. However, finding an audio grade 2.5 ohm 25 watt resistor may be a challenge. A good place for advice on locating such a part is Sonic Craft (www.soniccraft.com). I would give them a call. Sonic Craft stocks high quality Mills resistors in the 2.7 ohm and 4 ohm values you will need. They also have high quality Sonicap polypropylene film capacitors to replace the 12 uF mylar and 27 uF electrolytic capacitors in your crossovers.

    Another good parts vendor is Parts Connexion (www.partsconnexion.com). They have a much wider selection of premium parts and frequent 15% discount sales.

    There are lots of parts options, but if I had your speakers, these are the modifications I would do:

    1. Replace the 2.7 ohm and 4 ohm resistors with Mills MRA-12 wire wound resistors.

    2. Replace the 2.5 ohm 25 watt cermet resistor with an audio grade resistor of the same value and power rating. Can't offer any immediate suggestions for this part. It is going to take a bit of research on your part. Let us know what you find.

    3. Replace the 12 uF mylar and 27 uF electrolytic capacitors with 12 uF and 27 uF Sonicap Gen I film capacitors.

    4. Apply foam tape or some similar absorbtive material to the speaker baskets to reduce "ringing".

    5. Replace the stock binding posts with higher quality metal posts with metal retaining nuts. Maybe no sonic improvement, but certainly a better mechanical connection.

    6. Replace the grille cloths with a lighter, more sonically transparent fabric.

    7. Replace the stock SDA cable with one contructed from heavier gauge (12 AWG or thicker) wire.

    8. Remove the tweeter protection fuse from the circuit. (But only if you are certain that your listening habits and amplification will allow this.)

    Since the pre-1987 SDA's have wires directly soldered to the crossover circuit boards, I advise taking the extra time to attach labels to all wires and write labels on the circuit boards for easier reassembly. The SDA's from 1987 and later have snap-in wiring harnesses.

    There's lots of SDA modification info on the forum. Doing a search on "SDA modification" will produce an avalanche of info.:)
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    Last edited by DarqueKnight; 07-07-2007 at 06:28 PM.
    "Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
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    DarqueKnight - thanks for your insight and suggestions. I have been lurking on these boards for quite some time and have read all the threads regarding SDA crossover upgrades and modifications. Parts Connexion sells a Mills MRC50 2.5 ohm 50W resistor in a gold anodized aluminum housing - $4.95. The Mils MRC series requires a heat sink and its power handling is derated to ~25W without a heat sink. Michael Percy Audio sells a similar resistor ($5.95) that is derated to 20W with a heat sink. I plan on replacing the binding posts and add an additional binding post set for the SDA interconnect cable. For the caps I intend to go with Sonic Crafts and resistors Mills all around.
    The tweeters are SL1000's and the mid and base drivers are all the same, labeled MW6600X. I have not see this mid and base drive designation in any Polk literature or posting. For this reason I do not want to stray away from current crossover unless I change those drivers as well.

    This upgrade is on hold until I get the schematic for my signature edition Polk SDA 1's or an improved crossover for these or replacement drivers.

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    Welcome to the Club Polk Forums Embo! The best thing you could do is to replace those SL1000 tweeters with the RDO-194 soft dome tweeters from Polk. With the crossover and interconnect upgrade, you will be amzed at the difference in SQ.

    Good luck and welcome to the Forums!
    Carl

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    I hesitated to mention the RD0194 tweeter replacement because it is not an exact drop in replacement for the SL1000 as it is for the SL2000, plus, I have no listening experience with speakers that use the SL1000 tweeter. I can't say how much of an improvement the RD0194 would be over the SL1000. Here is a quote from a forum member who replaced the SL1000's in his SDA 1's:

    Quote Originally Posted by Gary Batson View Post
    I got the new tweeters in the mail today:D . I was not impressed with the cheep looking plastic faceplates . And black silk ? Must come from black worms. Looks like black plastic to me . Put me in a Pessimistic mood:( . I took the original tweeters with the heavy steel faceplates out and proseeded to install the new plastic tweeters. My mood got worse when I saw the screwholes didn't line up. Even worse is that they almost lined up meaning the new screwholes will be on the edge of the old screwholes possibly makeing the old and new holes useless . You would think that if Polk wanted to keep their vintage speakers alive, they would make a replacement tweeter that actually fit the speaker it was made for. I found that if I turned the tweeters cockeyed that two opposite corners on each tweeter would line up with the old screwholes. Not the way I wanted them installed. But a good temporary install just to see how they sounded. I put on Huey lewis - Small World and listened. Hum..sounds pretty much the same , But can't tell really? So I finnished the album. I think they might sound better? I'm getting happier. Then I put on Elton John - Yellow Brick Road. I notice my ears aren't hurting. That pointed end of a pencil stuck in my ear feeling that I got with the other tweeters. I'm actually enjoying the music:) . So I guess I did the right thing:D .

    Now...How to install these things right? I guess I'll have to drill new holes. :(
    The original thread is here: SDA1's Sound Bad
    Last edited by DarqueKnight; 07-08-2007 at 02:38 PM.
    "Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
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    This must have been a transitional speaker. The signature plaque may be there to cover up the port holes the SDA 1's had. The SDA 1 A's didn't have the ports.

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    My SDA1's are very "BRIGHT" sounding speakers. The high end overpowers the rest of the speaker. The original tweeters were very good sounding tweeters in my opinion. They were just too loud. The replacement RDO194 tweeters aren't as loud and easier to listen to.

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    Quote Originally Posted by Gary Batson View Post
    The signature plaque may be there to cover up the port holes the SDA 1's had. The SDA 1 A's didn't have the ports.
    Exactly. The SDA 1 to SDA 1A conversion specification states:

    "The ports are plugged with 1" diameter 3/4" long dowels...The dowel should be driven in flush with the baffle surface, and may be painted black after the glue dries, for better appearance."
    "Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
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    The SDA 1 Signature Edition do not have ports between the tweeters and midranges. The may have been plugged and covered by gold tone plaquard. I have not removed any of the drivers and felt around to see if the cabinet ever had the ports drilled. I will have to check next time I remove one of the midrange drivers. Also, the SDA 1 Signature Edition tweeters are fused - no polyswitch. DarqueKnight, I noticed in your initial response you suggested that the 4 ohm and 2.7 ohm resistors replaced with 12W Mills resistors instead of the more commonly chosed 5W versions - why?

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    Aside from the higher power rating, the 12 watt versions are larger and have a larger conductive area, which (theoretically) is supposed to result in better sound.

    A long time ago I compared the 5 watt and 12 watt versions and could not hear a difference. I just prefer the bigger, more robust 12 watt version.
    "Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
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    Thumbs up

    Very informative,:)
    as my SDA-1s also have the "Signature Edition" gold logo between the tweeters (now upgraded to RD-0194) and the mid/bass drivers.

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    What is your impression of the difference in sound between the SL1000 and RD0194?
    "Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
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    The SL-1000s always sounded like they were a bit "harsh" or bright at one frequency range and/or exciting a room resonance at that frequency.
    I sometimes found it was hard to listen to all of or more than one CD or album at a time. I was wondering if I needed to do additional room treatments beyond the thick cloth placemats I had taped on the wall at first reflection points of the tweeters (found with moving a mirror along the wall and sitting back in the recliner at the "sweet spot" to view the tweeters reflected in the mirror).

    From the forum postings I learned that there was indeed a recognized SL-1000 "spike" around 13 kHz (of however many dB) and of the availability of a replacement tweeter - the RD-0194.

    I ordered 4 RD-0194s from Ken Swauger on a Friday afternoon I think and they came in on following Tuesday and I got them installed that evening.

    At first the RD-0194s sounded "softer," but it did not take long to notice how they allowed longer periods of extended listening without ear "fatigue." The detail was still there and if anything was improved, but the highs were so much "smoother."

    I used the Pentatone SACD of Mozart Horn Concertos (w/Alan Civil and the
    Academy of St. Martin in the Fields, conducted by Neville Marriner) as a before and after test CD. This was one which exhibited some obvious harshness on particular notes (or higher harmonics) on the horn . In the first listen with the RD-0194s, I soon noticed the absence/disappearance of the "harshness" when the horn hit those certain notes in the score.
    I can remember thinking first "buttery" and then "smooth as silk, like the domes in the tweeters" to describe the difference.

    As soon as I got home from trip below Atlanta last year to purchase/retrieve SDA-SRS-2s from George Daniel, I couldn't help "pirating" the RD-0194s out of the SDA-1s and installing in the SRS-2s (George had redone the crossovers with Solen caps and Mills resistors!) and hooking those up to the speaker cables.

    As soon as I could afford to, I called Ken Swauger again to order another 4 RD-0194s for the SDA-1s.

    I find it hard to imagine anyone going back to the SL-1000s after hearing the RD-0194s for long enough to "adjust" ...
    Last edited by rlmacklin; 07-11-2007 at 11:42 AM. Reason: clarification

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