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  1. #1

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    Default 2B TL modification modification

    Mike (Face) has performed a mod to his 2B TL's that i am going to try to do this weekend on my 2B TL's. I believe it eliminates a few unnecessary jumpers in the tweeter circuitry which I am using a .05 ohm resistor to compensate for the lack of a poly switch. Mike's thread is the " A little love for the 2B TL's" in the vintage section.

    I am doing this as a thinking out loud thread to make sure I am doing it right and have the right thought process.

    It looks to me like the jumper on the + input just under the N on input and the jumper that goes under the S1 designation on the PC board can be eliminated.

    Option 1. If I am reading everything right it looks like the resistor can be installed between the + input just under the N on input and the small hole under the "Tweeter Output" writing on the PCB board next to the bigger hole above the L5 writing on the PCB.

    Option 2. The resistor can be installed between the + input just under the N on input and the hole on in the S1 location closests to the P1 on the PCB board.

    After looking at it I think option 2 will work on my x-over configuration.

    What do you guys think?

    Here are some pictures of my x-overs before I make any changes.
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    Last edited by MillerLiteScott; 10-17-2009 at 11:16 AM.
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D

  2. #2

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    After more thought it looks like the on lead of the 5.8 uF capacitor can be moved to the P3 location and eliminate the jumper from R2 also.
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D

  3. #3

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    Post #4 in http://www.polkaudio.com/forums/showthread.php?t=55888 contains links to Adobe .pdf format schematic for the "SDA CRS+ 1990 SL3000 Mod Sch.pdf" which is the same mod as the SDA-2B "TL".

    The path from the (+ [black]) binding post to tweeter is the same for both models and that schematic might be helpful.

    QUESTION: Would it be equivalent to use a 3.2 ohm resistor (.5 + 2.7) to make up for the removal of the .5 ohm polyswitch, or does it make a difference that the .5 ohm is located first and the 5.8uf cap is paralleled only over the 2.7 ohm? If a 3.2 could be used, that would simplify it even more.
    Last edited by inspiredsports; 10-17-2009 at 03:27 PM.
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  4. #4

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    The 5.8uf/2.7ohm parallel filter is a contour network. As long as you stay within 5%, you should be fine. So using a 3.0ohm resistor instead of a 2.7 shouldn't have a drastic effect on response, and at the same time will add a little more padding to the tweeter. If you don't mind adding another link to the chain, a .5ohm resistor in series before the HF circuit would work fine also.

    http://www.diyaudioandvideo.com/Calc...tour/Help.aspx
    "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

  5. #5

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    Mike would my Option 2 be the route to use and can I skip the the R2 to P3 Jumper and just take the 5.8uF right to the P3?

    Thanks,

    Scott
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D

  6. #6

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    "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

  7. #7

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    Well it turned out to be more complicated than I thought involving moving inductor leads and I did not want to get into that so I just substituted the .05 ohm resistor for the poly switch and I will see how everything sounds when I get everything back together in a couple of days.

    I have sealed the cabinet interior seams and drilled holes through the bottom of the cabinet and end panel to through bolt the studs for my spikes, 2 in front and 1 in the rear. I have to go to a specialty bolt store on Monday to get the size bolts I need to complete the install. They are not 1/4 20. I am also going to repaint the bottoms of my end panel even though you can't see them. Re apply mor-tite and sit back and listen.

    Scott
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D

  8. #8

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    Forgot to add the pictures of where I had to put the resistor.
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    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D

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