Schematics for AU90 transformer modification

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  • #610
    lotus123
    Participant

    D10 and HifiBluff, thank you both. I first got over the mechanical hurdle by building a mounting plate for AU90. The backplate for my M845s is spacious enough to fit a stainless steel plate to block off electromagnetic field from the bass transformer. Remember our sonic signals ride on the transformers. D10 if you can, I would very much appreciate to see a photo of the inside of you backplate so I can see the wirings (only when you happen to do the periodical checkup). Again thank you both.

    #611
    D10
    Participant

    Lotus 123 – I had all pics how I put acrylic plate but I can not find them .. Will try again .. If I take one of my backplate I will take a new ones for sure ..

    #624
    lotus123
    Participant

    Ha ha John, I think you were the one who sold me your unused AU90 about 5 years ago? If not, thank you along with D10 and Hifibuff for all your help. I am going to get interestingly busy to tackle the long awaited project over the holidays.

    I just responded to a SLOG member about the new Prestige 1 speakers. Don’t expect Earth Shattering improvement, although the AU90 mod was and is an earth shattering improvement over stock. I was bothered by the mid range suck out in the 100 hertz to 160 hertz region in my M845s. No reviewer ever highlighted this flaw in any of the reviews. Evidently, we listen with our wallets, and the pocket is deep enough to silence any upfront critics in this smoke and mirror cottage industry of hi end stuff. When I get to audition Lew’s system in Maryland with the mod, the speakers transformed. It became so efficient that the music came through with utterly clarity and punchiness. I guess all the signal was not being absorbed by the passive components in the stock back plates. Mostly importantly, the mid range suck out was remedied.

    #627
    John V
    Participant

    Hi lotus123,

    You are the one who purchased the AU90’s from me. And I thought I procrastinated, your as bad as me.;))
    What vintage M854’s do you have? I don’t recall that you owned them at the time you purchased the AU90.

    #628
    lotus123
    Participant

    Hi John, it’s good to hear from you again. This is important to me as my hair turned grey and now Will had passed away a few year back. And we met again in full circle. I am retired so I finally get around to updating M854PX vintage 2015.

    I want to clarify if the core inductor hooked up to the bass transformer should be removed also in the mod? Will told me to rip everything out except for the power supply, bass transformer and add small value extra high voltage caps between AU90 and bass transformer but did not mentioned core inductor.

    #646
    John V
    Participant

    Hi lotus123,

    Check out this thread on Audio Asylum. It contains Lew’s comments
    about the AU90 transformer and Will. Lew evidently did not remove the inductor connected to the bass Xformer while Will did. I think you would want to keep the inductor to block the highs from entering the bass transformer.

    https://www.audioasylum.com/cgi/vt.mpl?f=otl&m=35023

    #783
    Ezequiel64
    Participant

    Hello, and first time poster in this forum. Early last year, I purchased a one of pair of soundlab speakers known as the Renaissance R3&R4. They are a hybrid design with a panel for the highs and mid frequencies, and a dynamic woofer for the lows. In the past year I’ve been restoring them, as well as made some changes to the back plates in order to help alleviate a problem mentioned in this thread pertaining to the midrange suckout, that seems to be typical of the era around 2004. The Au90 transformer mod is very interesting, and wondered if anyone has the spec’s for it, so maybe it could be duplicated here in the states, or perhaps matched to one already made?

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    #786
    John V
    Participant

    Aside from the turns ratio I’m not aware that any other specs for the AU90 were ever available.
    I would contact Rob Mackinlay of ER Audio to see if can supply any
    specs. Also, if enough people have an interest maybe Rob would consider doing another run of transformers.

    http://www.eraudio.com.au/index.html

    #787
    Ezequiel64
    Participant

    I see, and thank you for the link. If I can get the specs,it seems getting a pair duplicated will be difficult. There is a transformer designed by Meno Vanderveen, and built by Plitron. It has a different turns ratio, and requires a resistor to tame some potential ringing. Has anyone tried with any success using it as a possible alternative?

    #790
    John V
    Participant

    Hi Ezequiel64,

    Could you take a picture of the underside of your backplates?
    I’m curious as to how it compares with the backplates for the full
    range SL ESL’s.

    #792
    Ezequiel64
    Participant

    John V,

    I believe the back plates to be ulmost identical. Along with some pics, here’s a diagram I found and modified to show how these were wired.

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    #796
    Ezequiel64
    Participant

    And here’s the high frequency section.

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    #798
    lotus123
    Participant

    Looks the same as my Majestic except it appears to have two inductor cores. I did not see brilliance control?

    #799
    Ezequiel64
    Participant

    Yes, I believe them to be very similar. The inductor and capacitor you see on top of the brilliance control, was there for a flatter frequency response in the midrange. I wondered at one point, if perhaps this filter was causing the issue, and confirmed with Dr West that may be the case because I run OTL’s. Dr West advised that I remove the inductor because it was causing a dip in inpedance that my amps won’t like. Also, I consider playing with the value of that cap in series with it, but found it sounded better with no cap at all!

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