Suggest: Line Isolation transformer. For home use with laptop. Rv!

Discussion in 'Pro Audio' started by Rv!, Sep 5, 2006.

  1. Rv!

    Rv! Guest

    Hi all,

    As in the subject really. I'm looking for a line level (or so) isolation
    to use with the new laptop. The lappy is noisy when running from the mains,
    all sort of horrible switching noises, fairly low level but annoying.

    What do you recommend? I want a low cost, but acceptable solution. No
    please, this is simpy for home use, general listening to music and email

    Rv!, Sep 5, 2006
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  2. Rv!

    animix Guest

    The lappy is noisy when running from the mains,
    Well.............if you're sure the noise is coming from the mains, these
    are *supposed* to address this problem at the source.
    animix, Sep 5, 2006
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  3. What are you trying to isolate from what? Where's your line level
    connection? Or aren't you using "line" in the audio sense?

    You may find that a mains-powered laptop just IS noisy. The onboard
    sound is generally utility-grade (to be kind) and is crammed FAR to
    close to other components. Quality sound from a laptop generally
    demands an external audio interface.
    Laurence Payne, Sep 5, 2006
  4. Rv!

    Scott Dorsey Guest

    Seeing as how you're in the UK, why not call Sowter?
    Scott Dorsey, Sep 5, 2006
  5. Rv!

    Scott Dorsey Guest

    That device is, indeed, a cheap isolation transformer.
    Scott Dorsey, Sep 5, 2006
  6. Rv!

    Ron(UK) Guest

    Ron(UK), Sep 5, 2006
  7. Rv!

    Arny Krueger Guest

    I had a small revelation about the possible quality of modern transformers a
    few months back. In a pinch I picked up Radio Shack's line-level signal
    isolator. I thought that it would stink. At any rate the thing really
    sounded pretty
    good when used as intended and performed well on the test bench, belieing
    its rediculously low cost.

    I tested Radio Shack's "Ground Isolator" 270-054 using
    test signals that maxed out around 2.5 v RMS. ZSource = 150 ohms, ZLoad =
    10K ohms.

    The measured performance was truely amazing for a pair of transformers case
    and cables selling for only $16.65.

    All IM, THD, and noise artifacts were at least 80 dB down with most in
    the -100 dB range or better. Frequency response showed a 2 dB peak at 20 Hz
    and then 10 dB down at 10 Hz. There was a 3 dB peak at about 51 KHz falling
    to about 10 dB down around 100 KHz. +0.5 dB at 20 KHz
    Arny Krueger, Sep 6, 2006
  8. Rv!

    Paul Stamler Guest

    Interesting! Did you measure the input impedances at 20Hz, 1kHz and 20kHz by
    any chance?

    Paul Stamler, Sep 6, 2006
  9. Rv!

    Rv! Guest

    "Arny Krueger" <arnyk@
    I just ordered one of those basic "Car grouong loop isolators" from Ebay.
    Got it
    as a sole bid with no reserve so stupidly cheap. Total was about $5 to my
    I guess this is probably going to be OK considering your last comments.
    When it arrives I'll post a comment regarding its suitability and quality.

    Rv!, Sep 6, 2006
  10. Rv!

    Julian Guest

    I have to say I also had a similar experience and bench tested it to
    my satisfaction

    Julian, Sep 7, 2006
  11. Rv!

    Arny Krueger Guest

    No, but I seem to recall that I did some experiments with varying the source
    and load impedances. My reciollection is that the transformer is reasonably
    non-critical with normal audio production source and load impedances for
    line-level equipment. It looks like it will also work fairly well with
    consumer audio gear, which is of course what it was intended for.
    Arny Krueger, Sep 7, 2006
  12. Rv!

    GregS Guest

    Since its not Radio Shack, I would beware.

    GregS, Sep 7, 2006
  13. Rv!

    Rv! Guest

    Hmm. Radio Shack suddenly Gods of Quality? Only joking about that but I
    would hope that the item ordered shouldn't be as bad as the first attempt
    and should be "decent" for my purpose. We'll find out soon. This part will
    be handy too since it has phono's which will plug straight into my Amp.
    Rv!, Sep 7, 2006
  14. Rv!

    Arny Krueger Guest


    It has been said that RS is selling a number of physically different
    isolators under the same part number.
    As does the RS item. It also comes with converters for use with 3.5 mm-based
    Arny Krueger, Sep 7, 2006
  15. Rv!

    Julian Guest

    I had the same experience as Arnie. I had a need for a quick fix and
    bought a radio shack and thought it'd suck but sounded pretty good so
    I bought a couple more and did tests on them, both the older version
    which had a lot more iron in it and the newer version which is much
    lighter weight and to my surprise they tested good and sounded good.
    The newer one was slight better in frequency response as I recall.

    I thought about suggesting it to you, but I thought I'd get probably
    laughed at!

    Julian, Sep 8, 2006
  16. Rv!

    Rv! Guest

    "Julian" <JulianPAdamsNo@

    It seems that as slong as the company has tried to get a decent bandwidth
    tranny, they seem to work adequately. I can't wait for mine to arrive! :)

    Rv!, Sep 8, 2006
  17. Rv!

    Julian Guest

    I tested 2 of them. A newer model that was very light weight and had
    a plastic like feeling and an older model that was heavier and
    appeared to have more iron in it. I expected the newer lighter weight
    model to have poorer specs but was pleasantly surprised when it's
    frequency response was actually a hair better than the older model.

    Julian, Sep 8, 2006
  18. Rv!

    Scott Dorsey Guest

    Don't worry so much about the swept sine response right off. What does
    a 1 KC square wave look like on the scope? And what happens when you change
    the loading?
    Scott Dorsey, Sep 8, 2006
  19. Rv!

    Julian Guest

    Probably not perfect. Sounds better than with the hum however :)

    Julian, Sep 9, 2006
  20. Rv!

    Scott Dorsey Guest

    Yes, but the thing is that if it turns out to be a transformer whose impulse
    response changes radically with loading, that's a thing you want to know.
    Because now you can add a shunt resistor to it so that it will ring just a
    tiny little bit (one peak should be visible on the scope, not two, and the
    peak should only go up a little bit). Then it'll sound still better, for
    a minimal added cost of one resistor.
    Scott Dorsey, Sep 9, 2006
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