A3 – what are the latest updates for backplates ?

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  • #276
    supportmac
    Participant

    Dear Soundlab lovers, I have recently purchased on eBay a faulty pair of A3 speakers. As I live in France it is complicated and expensive to send them to USA for a repair. So I’ll try to repair them here in France, and if it does not work will ultimately send them to USA. Does any of you have some schematics or pictures of the latest version of A3 electronics? It looks like A3 board have passed trough several modifications. I understand that the latest version is using Toroidal transformers (what model of transformer?) and that some other changes have been made. I’m using Atma Sphere amplifiers, so if you know some tweaks specific for OTL amplifiers, that also would be very welcome. Thank you very much for all your help!

    #277
    John V
    Participant

    Hello Supportmac,

    Attached is a wiring diagram for the Toroid II transformer along with a few pix. of the Connsumate Backplate.
    A couple of notes:
    1. The resistors and capacitors for the high frequency filter of the Toroid are as follows:
    Resistors: 4 Dale 48 ohm 50W 1% non inductive wired in parallel to
    give a net resistance of 12 ohms.
    Capacitors: 3 8ufd Audiocap Theta’s wired in parallel for a
    total capacitance of 24ufd.
    2. The midrange filter is the coil box shown in the diagram. Note that there is a separate 15 mhy iron core coil wired in such a way to give 20 mhy with the 5 mhy coil in the module.
    3. The values of the high voltage mixer have changed over the years.
    Currently the value is 2.2 nfd. I’ve attached a diagram showing how to measure the value.
    4. The bias supply is now a regulated unit so that variations in line voltage will not affect the bias level of the panel.
    5. The Bass transformer has not changed over the years so you should be able to use the existing one.

    I’ve also attached a few pix. of the current backplate

    The resistors and capacitors are available online. The other parts, transformer, coil, mixer, bias, switches, new blank backplate, can be purchased from the factory. I would call Connie and discus it with her or you can email Roger.

    Should you have further questions don’t hesitate to ask.

    Good Luck,
    John

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    #284
    supportmac
    Participant

    Hello John, thanks very much! This is very helpful! That’s very kind of you!

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