Schematics for AU90 transformer modification

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  • #575
    lotus123
    Participant

    Anyone can help in getting the schematics for the backplate modification for the AU90 transformer? This mod was very popular back in the 2011 with members like Lew and Will from KIS audio in Australia.

    #584
    D10
    Participant

    Why don’t you contact guy directly in Australia. I used to have schematic but I can not find it . Mod is very simple – you connect AU90 instead of toroidal transformer and take out entire crossover network – as I remember. So no caps and resistors in backplate. AU90 has natural frequency slope with bass transformer.
    Will – who was real SL enthusiast and genius used his SL with wide open tone controls on backplate – I do the same .
    D

    #586
    bk12
    Participant

    I can’t find the schematics either. Unfortunately, I believe Will, the Australian that figured this out and sourced them has passed away a year or so ago.

    #587
    Earlinarizona
    Participant

    I had this from long ago but don’t know if this is what you are looking for.

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    #589
    D10
    Participant

    Damn! I will take a hard look to find it this weekend!
    Unfortunately Will passed few years ago …
    D

    #590
    lotus123
    Participant

    D10, wow it’s been that long even Will passed away last year. I remembered Will even removed the inductor core. Did you remove the inductor core as well?

    I wonder where is Lew now? He and Will were the foremost in directing Dr. Roger West to revamping the backplate with a more efficient tranny.

    Earlinarizona, thank you so very much.

    #591
    lotus123
    Participant

    Earlingarizona, the schematic is for stock not the AU90 mod. I recalled many years ago Lew on the forum told me to insert two small value but extremely high voltage caps as he did.

    #595
    D10
    Participant

    Lotus 123, wow .. no way Will passed last year .. honestly I forgot where I read about it . It has to be in old SLOG forum .. too busy to look up for it
    D

    #596
    hifibuff
    Participant

    I found this from my dusty files. These were a tight fit in my A3 backplates.

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    #602
    lotus123
    Participant

    @hifibuff, thank you. Did you encounter issues with wiring the two transformers out of phase? Did you keep the core inductor or had them removed like Will did?

    #603
    hifibuff
    Participant

    No problems. Since my A3 are from 1989 the backplates are small. I had to remove the hi frequency pot (it was bypassed with a resister but left if to fill the hole), mount the switch PS vertically and use spacers under the mixer to clear hardware on the backplate.

    #604
    D10
    Participant

    The last pic is identical as mine . The problem is that AU-90 could not fit in my U-1. So you need to use 2 acrylic plates join together with cement – one should have holes to fit on backplate and another to fit transformer. I do not use inductor in my SL
    D

    #605
    John V
    Participant

    Hi lotus123,

    Here is a copy of am email I received in 2012 showing the brackets made to hold the AU transformers:

    From: David [mailto:dmcclesk@swbell.net]
    Sent: Sunday, August 28, 2011 10:04 AM
    To: ‘acousticsupplies@gmail.com’
    Subject: FW: brackets for tranformers

    Hey Will – Here is the info I sent Lew on subject…Let me know if you have any questions…David

    PS: Make sure when you do the cutouts in plate 3 that you leave enough room on the outside edge for the machine screws. They are right at the edge…

    From: David [mailto:dmcclesk@swbell.net]
    Sent: Thursday, August 18, 2011 6:51 PM
    To: ‘markoffl@yahoo.com’
    Subject: RE: brackets for tranformers

    Hey Lew – Here is a quick sketch of how I made the mounts. All three pieces are ¼” acrylic. The cut outs should be large enough for you to get a nutdriver on the nuts that fasten the mount to the backplate. I can’t replicate them as I would have to take my backplates apart to measure spacing and sizes again, etc…The finished mount is removable. The 4 – 8/32 or 10/32 machine screws should be tightly threaded from the underside of plate 3 to avoid slippage when fastening the transformer nuts…Let me know if you have any questions…There may be a more elegant solution but I was in a hurry when I made them…After the picture (below) of the backplate was taken, I removed the brilliance pot from the circuit and hardwired the transformer connections with Valhalla..only because I had it already from the original backplates.…Also while the 1.5 sledgehammer is still in place I have it switched out. I’ll probably remove it at some point. Let me know if you have any questions…

    David

    —– Forwarded message —–
    From: “Lewis M” <markoffl@yahoo.com>
    Date: Thu, Aug 18, 2011 10:35 am
    Subject: brackets for tranformers
    To: “dmcclesk@swbell.net” <dmcclesk@swbell.net>

    Dear David,

    Is there any chance you can get me a pair of the brackets you made or had made for mounting the 90:1 transformers in the backplate? I would pay all costs, of course. If not, perhaps you can send me a drawing or plan for making them here.

    Lew

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    #608
    D10
    Participant

    Ha! Exactly the same schematic I had! It is very easy to make it !

    #609
    D10
    Participant

    Do not use too thick acrylic plates – transformer could hit your floor

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