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  1. #1
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    speakers reborn as LS3/5a clone

    One of my old speaker systems consisted of a set of KEF drivers I brought back from London in 1979 - a set of veritable T27, B110 and B139 units that got put into a set of cabinets. The tweeter and midrange went into a small custom built cabinet the size of a LS3/5a and the woofer went into a transmission line box. The whole thing had an active crossover and was tri-amped. Evenutally I moved on to other speakers. The B139 drivers were sold on eBay but I hung onto the small boxes.

    A couple of months ago I decided to dig these out of the basement and make them my computer speakers. Since they had no internal crossover, I just got a cheap 3KHz crossover from Parts Express. Not too bad but I knew they could really sound much better.

    So a couple of weeks ago I ran down the schematic for the original LS3/5a's and ordered the parts. I had to etch the circuit board from scratch and hand-wind one of the inductors since I couldn't find a pre-wound 0.24 mH coil. (That's the green-wired one at the upper left corner.)

    Anyway, I finished building and testing them this afternoon and got them installed. While the speakers take a hit on efficiency, the sound improvement is stunning. It is like a deep stage has opened in between the speakers. It really sets you back a step to hear this type of sound coming from your desktop computer. (I'm using a Trends Audio amp, not too much power but great quality and more than enough for the desk since this is a seriously "near field" monitoring experience.)

    A fun project and a great re-use of some old, but great speakers.
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  2. #2
    Forum Regular Registered Member aevans's Avatar
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    Glad to hear you like your setup.. you got any pics of the speakers, I'm not familiar with them and I'd like to see what you've got.

    rules of thumb: crossovers are the best place to spend your money on diy speakers.

  3. #3
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    I'll try to post a photo here in a day or two. The boxes are not too big (6.5" X 11.3" X 6.7" deep) and these were home-brew cabinets in an oak veneer. Given these are approaching 30 years old and have had several moves and lots of time in the basement they are not real fancy to look at. If you want to get a feel for the legendary official LS3/5a, visit the enthusiasts' web site at http://www.ls35a.com/.

    (One other note, this is not my main system.)

  4. #4
    Forum Regular Registered Member aevans's Avatar
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    I understand it's desktop - I just wanted to get a feel for how big these were b/c most serious speakers of that era were very large and I just could not see that fitting on a regular desk. looks like a very cool speaker, do your cabnets have the foam surround and old time grill?

  5. #5
    Shostakovich fan Feanor's Avatar
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    Nice job

    Quote Originally Posted by mlsstl
    One of my old speaker systems consisted of a set of KEF drivers I brought back from London in 1979 - a set of veritable T27, B110 and B139 units that got put into a set of cabinets. The tweeter and midrange went into a small custom built cabinet the size of a LS3/5a and the woofer went into a transmission line box. The whole thing had an active crossover and was tri-amped. Evenutally I moved on to other speakers. The B139 drivers were sold on eBay but I hung onto the small boxes.

    A couple of months ago I decided to dig these out of the basement and make them my computer speakers. Since they had no internal crossover, I just got a cheap 3KHz crossover from Parts Express. Not too bad but I knew they could really sound much better.

    So a couple of weeks ago I ran down the schematic for the original LS3/5a's and ordered the parts. I had to etch the circuit board from scratch and hand-wind one of the inductors since I couldn't find a pre-wound 0.24 mH coil. (That's the green-wired one at the upper left corner.)
    ...

    A fun project and a great re-use of some old, but great speakers.
    No doubt at all that the crossover is critical to any loudspeaker design.

    Nice job etching your own board; that's something I've never attempted. Did you consider point to point wiring? (That I've done.) The wiring on your hand-wound coil looks to be much smaller gauge than the inductors, (or maybe it's just the picture): is this according to specification?

  6. #6
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    Actually none of the coils are "to spec" since the original LS3/5a speakers have cored inductors in all spots and I used air core. However, the green coil is the inductor bleed to ground on the tweeter following the first tweeter input capacitor so I didn't worry as much about the 26 gauge wire. The larger coils on the bottom half of the board are for the woofer.

    Circuit board paths can be just as good as point-to-point wiring. First, I made sure all the copper paths were quite wide; they are about 1/2". Then I very liberally coated the paths with a thick layer of good solder so the electrical paths on the board are equivalent to a fairly heavy gauge wire.

    I'm under no illusion that I now have a set of "genuine" LS3/5a's to the original BBC specs, but for under $100 in parts and re-using some speakers that many would have discarded or sold cheap long ago, I've got a pretty dang good set of speakers for my computer now!

  7. #7
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    aevens, here is a photo of the computer desktop with the speakers. Nothing fancy looking, but they're right there in front of you!
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  8. #8
    Forum Regular hifitommy's Avatar
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    classic drivers

    the b110s were maybe the first to be developed using mlssa technology and are still a geat basis for any speaker.

    the t27s are a bit limited in the top but that is easily overlooked given their otherwise xlnt performance.

    enjoy!
    ...regards...tr

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