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Thread: SL3-eXtreme Center channel speaker – a design and build story

  1. #16
    Super User JonFo's Avatar
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    Default Physical Build of ESL drive board

    Now that the design is done, time to build.

    First challenge: the OEM board is huge, and since we are cutting the SL3 down to just 4’ of total length (size of panel only), we need to repackage the electronics.

    Since I’m lazy (cough), I decided to see how much of the OEM board I could reuse. After some measuring, I decided that the ‘bottom’ 4” of the panel that contains the Input, power and bass-contour switch could be repurposed as the new vertical ‘top face’ of the rear, so I’d need to cut 4” into the board.
    To fit the rest of the stuff, and have something that slid into the opening of the SL3 in a horizontal fashion, I’d need to fit the 9.5” opening and keep to an 11” depth (and no part could protrude more than 3” vertically).

    More measurements and the rest of the board was cut up to meet this criteria.

    Of course, before any cutting, I had to totally remove all parts from the board.

    After the cuts, I re-laid out the elements and screwed them on. Soldered leads together and basically have what you see here.

    The stuff on the left are all the removed passive components. Good thing too, as they would not have fit.
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  2. #17
    Super User JonFo's Avatar
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    Default Another view of new board

    Here is another view of the newly re-arranged ESL drive board
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  3. #18
    Member Peter Hogan's Avatar
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    Default

    Quote Originally Posted by JonFo
    The Orange output of the transformer goes to the high-voltage board to provide a reference signal for the Diaphragm and to supply the negative Signal for the Front Stator via the Blue line on BB4.
    Additionally, a reference signal ground is fed to the BB4 on the High-voltage board and another is fed straight to the front stator via the second blue lead.

    Simple, right ?
    Hi,
    Double check the high voltage wiring. The ML's I've seen have the transformer outputs going to both stators, and the bias high voltage between the transformer output center tap (that you haven't shown) and the diaphragm film. That way the transformer signal drives one stator negative, the other stator positive, and vice versa for the other half of the waveform, for a push-pull effect on the diaphragm.

    Peter
    Friends don't let friends buy Bose.

  4. #19
    Super User JonFo's Avatar
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    Default

    Quote Originally Posted by Peter Hogan
    Hi,
    Double check the high voltage wiring. The ML's I've seen have the transformer outputs going to both stators, and the bias high voltage between the transformer output center tap (that you haven't shown) and the diaphragm film. That way the transformer signal drives one stator negative, the other stator positive, and vice versa for the other half of the waveform, for a push-pull effect on the diaphragm.

    Peter
    Thanks Peter. You are correct that some models have the step-up wired as you describe. There are schematics floating about that depict the orange tap feeding the front stator and the gray wire feeding the rear, with a center tap feeding the high voltage board.

    However, the SL3 units I have are wired as I described. I didn't even disconnect the stock wires from the High-Voltage board, xformer nor the connector.
    On my xformer, all other taps are wrapped down and unused as you can see in the pic. So no center output tap was ever used.

    This had me scratching my head for a while, but given that it’s the stock wiring (and I have pics of ‘before’ to double-check, plus the other SL3 unit, I feel comfortable this is correct.
    It looks like ML had a design change in the HV board at some point as my boards are from Feb of ’98.
    So anyone reading this and planning a mod to their ESL drives should take this into consideration, as there are various modes of wiring these things depending on which rev of the HV board you have.
    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  5. #20
    Super User JonFo's Avatar
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    Default Box prep

    Here are some pictures of the build of the Line Array Box.

    As described above, it’s a 4’ box made from Ύ" 12-ply Baltic Birch plywood. It features two internal braces plus cutouts in the rear for two binding post cups and six cutouts in the front for the Extremis.
    The box uses biscuit-joins to keep alignment and the sides and tops all glued and screwed together. All edges are routed with 1/8" roundover.

    Also seen in this shot is the cut-down version of the SL3. The masking tape on the rail-fronts is to protect the Velcro and foam strip from dust and paint.
    The SL3 is cut to just the length of the panel, or 4’.
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  6. #21
    Super User JonFo's Avatar
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    Another shot of the Line Array box before paint.
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  7. #22
    Super User JonFo's Avatar
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    Default Painted Box

    And here it is in its glorious flat black.

    Again, it sits behind a screen with microperfs, which let about 10% of the light through, so nothing shinny or reflective is allowed back there
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  8. #23
    Super User JonFo's Avatar
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    Default Mounting Board

    Now we need to mount the painted Line Array box and the ESL frame to a mounting board.
    Since the Infinite Baffle is 23x23” and the sum of the widths of the SL3 and the new LA box are exactly 23”, we make our mounting plate 23” x 20”

    This will allow the units to be screwed in from the bottom of the mounting plate, then the mounting plate itself will be screwed onto the IB box. It will not be going anywhere. This will be the most solidly mounted Center I’ve yet to see

    This shot shows the ESL frame and the LA Box screwed into the plate, which in this pic is upside down so we can actually put the screws in.
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    Last edited by JonFo; 12-31-2008 at 06:20 AM. Reason: spelling
    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  9. #24
    Super User JonFo's Avatar
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    Default Plate Bottom

    Here you can see the bottom of the plate with the screw patterns to hold in the units. The screw holes are counter-sunk so the plate will sit flat on the IB surface.

    Next step is to take the naked (but now drilled out for the new units) mounting plate and get the correct screw pattern to put into the IB.
    Once that’s done, I’ll route edges and paint.
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  10. #25
    Super User JonFo's Avatar
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    Default Wiring up the Woofers

    To achieve a reasonable load on the amp with six 7 to 8 Ohm speakers, you need to wire them up in such a way that they produce a load somewhere in the range of 4 to 16 Ohms.
    Therefore, we will combine series and parallel wiring techniques to achieve our goal.

    Use two series wired sets of three speakers each. Each set is paralleled into the amp for a total load of around 11 Ohms.

    Here is the diagram of the parallel sum of the two sets
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  11. #26
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    Default Set of series wired drivers

    And here is the one with the series set layout, this done for each set of three speakers:

    Since the Extremis is rated for 100w each driver, running them at 1/3 rated handling is quite safe. We could even double the power and still be well within the design limits.

    The wiring will be done in such a way that each series set will go to its own binding post cup. The parallel wiring will happen with the feed connectors.

    This gives us the option of wiring it up with two channels of amplification (albeit, with much higher impedance).
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  12. #27
    Super User JonFo's Avatar
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    Default Wiring Diagram

    And here is the guide I made to help me build the wiring loom.

    I use a high quality OFC, silver clad wire along with gold plated crimp-on spades.
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  13. #28
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    Default Driver assembly

    Here is a shot of the drivers all lined up on the box and wired up. The mounting holes have been drilled out and the box stuffed to 100%.
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  14. #29
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    Default Drivers Mounted

    The drivers are now mounted and the unit is ready to test.
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

  15. #30
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    Default Testing

    Before I mount the Line Array and the SL3 to the mounting base, I first need to run some test and measurements.

    Each unit is hooked up to a an amp channel fed directly by my ETF measurement system. The mic is left at exactly the same point throughout this entire test to ensure comparisons are equal.

    Here is the SL3 element alone being tested.
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    Jonathan

    System #45 (Monolith IIIx, Sequell IIb, SL3XC)

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