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Thread: Focal-JMLab Chorus 706S project

  1. #1
    Join Date: Jun 2011

    Location: Tallinn, Estonia

    Posts: 153
    I'm Juha.

    Default Focal-JMLab Chorus 706S project

    Won a pair of these on local Tallinn internet auction site. They were advertised with blown and replaced tweeters. Original Focal tweeters had been broken with excessive volume. They had put in inexpensive Visaton DTW 72 tweeters as replacement.

    Started listening test today. I found that there was an issue with a crossover. One crossover had a blown a 7W resistor. It had gotten so hot as to melt plastic (a plastic cable tie). I replaced the resistor. The heat had caused a cold soldering issue. So I reheated most crossover printed circuit board connections. It did not help that Focal had hidden the actual board connections with a multi-layer printed board.

    Well, even with cheapish replacement tweeters these speakers sound good.
    But something is lacking. Focal tweeters are expensive (about 90 eur each).

    What would bring more tweeter character? Some classic British dome tweeter or Monacor RBT-95. What do you usually use. Crossover frequency is 2400 Hz.


  2. #2
    Join Date: Jul 2010

    Location: North Cambs UK, Earth, Sol, Orion - Cygnus arm of galaxy

    Posts: 11,166
    I'm MadeOfDeadGiantStarsThatExplodedEonsAgo.

    Default

    You might like to find out the sensitivity of the replacement tweeters in comparison to the original Focals It's quite probable that they aren't the same, I know Focal units can be quite sensitive, some of them are 95DB/1W

    Not suggesting the ones in this speaker were, but you might find that judicious tweeking of certain resistors in the tweeter section of the crossover may well reap dividends
    Bests, Mark



    "We must believe in free will. We have no choice" Isaac Bashevis Singer

  3. #3
    Join Date: Jun 2011

    Location: Tallinn, Estonia

    Posts: 153
    I'm Juha.

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    Focal woofers are rated at 89 dB. Model Focal 6 V 3254. The Visaton replacement tweeters are 91 dB. They are a decent match.
    But the sound is bog standard. There is no special airyness. No well defined soundstage.

  4. #4
    Join Date: Jul 2010

    Location: North Cambs UK, Earth, Sol, Orion - Cygnus arm of galaxy

    Posts: 11,166
    I'm MadeOfDeadGiantStarsThatExplodedEonsAgo.

    Default

    Yes looks like the tweeters can be made to work with the woofers as they are more sensitive What you need to find out now is the sensitivity of the original Focal tweeters, they might have been 93Db sensitive, in which case you'd need to fiddle with any resistors on the tweeter side of the xover to increase power to the Visaton tweeters

    Or are you saying that the Focal tweeters were exactly the same sensitivity as the new Visatons?
    Bests, Mark



    "We must believe in free will. We have no choice" Isaac Bashevis Singer

  5. #5
    Join Date: Jun 2011

    Location: Tallinn, Estonia

    Posts: 153
    I'm Juha.

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    Thank you for advice.
    There is no information available on the original tweeter for Focal-JMLab 706S.

    After some Googling and research I finally bought Genelec tweeters. I found a pair of Genelec 1029A monitor tweeters on Ebay. It is going to take 10 days to get them from Hong-Kong to Estonia.

    These are manufactured by Vifa. They have been proven good by thousands of studio monitors.

    It will be interesting to see if they make a big difference. This is "Visaton common plastic" vs. "handcrafted studio stuff".


  6. #6
    MartinT Guest

    Default

    What about the physical fit, Juha? How will you mount them?

  7. #7
    Join Date: Jun 2011

    Location: Tallinn, Estonia

    Posts: 153
    I'm Juha.

    Default

    I received Genelec tweeters from Kowloon, Hong Kong. Only took 7 days.

    Used, but look clean and not broken. These are heavy (350 grams) with dual powerful magnets. Titanium domes. No markings even for + / -. Both 5 ohms.

    First I was going to make a bigger hole where the old tweeters were and fix these with metal clips on the outside (there is no screw holes as they sit inside the Genelec speaker that has a metal wave-guide).

    But just to test I put them on top of the cabinets facing up. Wow. Very wide dispersion. With eyes closed I would swear they are facing me and not up.

    The sound. Percussive elements of piano, cymbals and sibilants in human voice are perfect. Sound stage good. Well, I expected this. These are from a famous studio monitor.

    Cost: Genelec tweeters 77 USD with postage. Chorus 706S pair 50 USD.
    Cheap as chips.

  8. #8
    Join Date: Jun 2011

    Location: Tallinn, Estonia

    Posts: 153
    I'm Juha.

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    This is the finished speaker:




    I tried L-Pad to get the level of the tweeter down 2 decibels. In the end this was not needed.

    I was thinking that maybe after 10 years these tweeters will be valuable. These and other Genelecs are the ones used by BBC to monitor audio. Genelec does not give much info on their speaker elements. I did not find many available on ebay.

    Listening equipment used: Squeezebox Touch, Quad 303 (Dada), Quad 522, Triad Design System Seven subwoofer

  9. #9
    MartinT Guest

    Default

    Well done, Juha. The result looks fine and obviously pleases you. Wish I could say the same for your camera

  10. #10
    Join Date: Jul 2010

    Location: North Cambs UK, Earth, Sol, Orion - Cygnus arm of galaxy

    Posts: 11,166
    I'm MadeOfDeadGiantStarsThatExplodedEonsAgo.

    Default

    Hmm, I'd see what I could do about the method of attaching the driver to the enclosure in all honesty. If you have a decent match then some work would pay serious dividends imho.

    Get some alloy plate the same thickness as the step in the tweeter & a hole machined the same size as the step on the front, make sure it's bigger than the overall diameter of the tweeter & countersink it in so it's flush with the baffle

    Three holes drilled & countersunk & appropriate screws or bolts & T nuts will see a big improvement on the arrangement you have there Juha

    If it's good now I reckon it'd be worth the messing about to do it right
    Bests, Mark



    "We must believe in free will. We have no choice" Isaac Bashevis Singer

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