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  1. #1

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    Default SDA Dreadnought Isolation Transformer Output Voltage Balance

    One question that comes up about the Dreadnought 1:1 toroidal isolation transformer is, since we are using the transformers in an application with bi-directional signals, will the SDA signal be imbalanced. The answer is no. Although there is a small difference in output between the primary to secondary and secondary to primary directions, the difference is inaudible, on the order of fractions of a dB.

    This subject was first discussed in posts 62-71 of this thread...

    The-AI-1-Dreadnought-Project-Pt.1


    ...and again in posts 167-174 of this thread...

    The-AI-1-Dreadnought-Project-Pt.2-Upgrade-to-1000VA-Transformer

    and most recently in posts 11-18 of this thread:

    Dreadnought-Assembly-Questions

    When I measured the left and right stereo and dimensional outputs of the Y236906 800VA transformer in 2008, there was a few percent difference in the outputs of each direction, but it certainly could not be considered as an "imbalance".

    Table 1

    In terms of dB, the differences in voltage amplitudes between channels are:

    60 Hz

    0.12 dB stereo, 0.26 dB dimensional.

    1000 Hz

    0.38 dB stereo, 0.39 dB dimensional.

    With all of the things going on in a stereo sound field, most people would not (or cannot) notice a difference of 0.1 dB to 0.4 dB difference in sound level between channels.

    Consider that any isolation transformer, even the one used with the original AI-1, will have a small difference in output when comparing primary to secondary direction and secondary to primary direction. This is unavoidable since a 1:1 isolation transformer must include a small step up function to account for transformer losses. It is unavoidable that a signal going in the secondary to primary direction will see a small step down function. However, the output differences between directions should be (and are) inaudible and should be (and are) within the range you would expect from differences in amp channels and differences in loudspeaker drivers and crossover components. The difference between the outputs of each direction will also vary with frequency. Table 2 shows the output voltage differences according to direction among the original AI-1, 800VA Dreadnought, and 1000VA Dreadnought. The SDA circuit operates from 1600 Hz down.

    Table 2


    Figure 1. Left to right: original Polk AI-1 Non-Common Ground Interface, 800VA AI-1 Dreadnought, 1000VA AI-1 Dreadnought.
    "Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
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  2. #2

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    Default

    Thank you, DK, for spending the time 'n' effort to address this.

  3. #3

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    Thanks DK
    Home Theater/2 Channel:
    Front: SDA-2ATL http://www.polkaudio.com/forums/show...ished...Almost
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  4. #4

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    i have a stupid question, is this device the same type of isolation transformer that would have been used on 120 volts line, like that used for some electronics repair? the reason i ask is i own 3 isolation transformers that are kinda used as door stops at 20 amps, they are a pull from a perfusion system so it's overkill in it's ratings
    There is no cure....
    Luxman M117, SDA SRS 2.3, rear monitor 10, back rear bose 4.2, valodyne sub and 2 Onkyo m-504 amps Onkyo TX-NR709
    8mm, 7.62x39mm

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    These are audio quality transformers, not really sure that what you have is.
    'Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

  6. #6

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    what i have is a medical grade isolation transformer for 115 in and 115 out, 1:1 ratio, what i don't know is it's impedance or it's inductance or DCR, i can measure some of it after i dig one out.
    There is no cure....
    Luxman M117, SDA SRS 2.3, rear monitor 10, back rear bose 4.2, valodyne sub and 2 Onkyo m-504 amps Onkyo TX-NR709
    8mm, 7.62x39mm

  7. #7

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    I think i found the numbers i need in another thread. What has my curiosity are the similarities to equipment i own.
    There is no cure....
    Luxman M117, SDA SRS 2.3, rear monitor 10, back rear bose 4.2, valodyne sub and 2 Onkyo m-504 amps Onkyo TX-NR709
    8mm, 7.62x39mm

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