Getting matching transformer from telephone

Discussion in 'Electronic Components' started by Paul B, Dec 27, 2008.

  1. Paul B

    Paul B Guest

    I am looking for some 1-to-1 matching transformers to connect varioua
    audio devices to my PC. I usually get noises and hum.

    These line matching transformers are not so cheap at about £6 or 7
    each.

    Telephones seem to suppress line noise and hum rather well so I
    figure the components they use are probably of half-decent quality.

    If I strip down some landline phones I 've got here, then will there
    be a matching transformer in each one? Or is their technology
    different now?
     
    Paul B, Dec 27, 2008
    #1
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  2. Paul B

    Franc Zabkar Guest

    On Sat, 27 Dec 2008 22:03:10 GMT, Paul B <> put
    finger to keyboard and composed:

    >I am looking for some 1-to-1 matching transformers to connect varioua
    >audio devices to my PC. I usually get noises and hum.
    >
    >These line matching transformers are not so cheap at about £6 or 7
    >each.
    >
    >Telephones seem to suppress line noise and hum rather well so I
    >figure the components they use are probably of half-decent quality.
    >
    >If I strip down some landline phones I 've got here, then will there
    >be a matching transformer in each one? Or is their technology
    >different now?


    FWIW, you may find some "600 ohm" transformers in old modems, ie those
    with a "non-silicon" DAA.

    - Franc Zabkar
    --
    Please remove one 'i' from my address when replying by email.
     
    Franc Zabkar, Dec 27, 2008
    #2
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  3. Paul B

    Phil Allison Guest

    "Paul B"
    >
    >I am looking for some 1-to-1 matching transformers to connect varioua
    > audio devices to my PC. I usually get noises and hum.
    >
    > These line matching transformers are not so cheap at about £6 or 7
    > each.



    ** You can get a stereo pair of "audio line isolation transformer s" from
    places that supply car audio gear - these come with male and female RCA
    plugs which you can change to mini-jacks at one end.


    > Telephones seem to suppress line noise and hum rather well so I
    > figure the components they use are probably of half-decent quality.



    ** Nonsense.

    Generally phones have no such transformer inside ( no need exists as a phone
    is not grounded like your PC is ) and in any case they are not suitable for
    hi-fi audio.



    ...... Phil
     
    Phil Allison, Dec 28, 2008
    #3
  4. Paul B

    Salmon Egg Guest

    In article <Xns9B81E055CF04D74C1H4@69.16.176.253>,
    Paul B <> wrote:

    > I am looking for some 1-to-1 matching transformers to connect varioua
    > audio devices to my PC. I usually get noises and hum.
    >
    > These line matching transformers are not so cheap at about £6 or 7
    > each.
    >
    > Telephones seem to suppress line noise and hum rather well so I
    > figure the components they use are probably of half-decent quality.
    >
    > If I strip down some landline phones I 've got here, then will there
    > be a matching transformer in each one? Or is their technology
    > different now?


    D Do you meanj isolation transformer or matching transformer. There is
    no impedance matching (transformation) using a 1-to-1 transformer.

    Bill

    --
    Private Profit; Public Poop! Avoid collateral windfall!
     
    Salmon Egg, Dec 28, 2008
    #4
  5. On Sat, 27 Dec 2008 22:03:10 +0000, Paul B faxed us with....

    > I am looking for some 1-to-1 matching transformers to connect varioua
    > audio devices to my PC. I usually get noises and hum.
    >
    > These line matching transformers are not so cheap at about 6 or 7 each.
    >
    > Telephones seem to suppress line noise and hum rather well so I figure
    > the components they use are probably of half-decent quality.
    >
    > If I strip down some landline phones I 've got here, then will there be
    > a matching transformer in each one? Or is their technology different
    > now?


    Plenty of 600 ohm transformers around. Maplin keep them for one thing.

    As for 'quality', a telephone line is balanced, hence noise tends to
    appear out of phase and is cancelled out. Hum would tend to indicate a
    ground issue with a line. It's nothing to do with the quality of the
    parts, just the design of the system.


    --
    Replica Watches - TRY WALMART
     
    Blah Blah Blah, Dec 28, 2008
    #5
  6. On Sat, 27 Dec 2008 22:03:10 GMT, Paul B <> wrote:

    >
    >If I strip down some landline phones I 've got here, then will there
    >be a matching transformer in each one? Or is their technology
    >different now?



    It isn't a matching transformer. It is for isolation purposes, and
    yes, there is one in all phones that attach to Ma Bell.
     
    Archimedes' Lever, Dec 28, 2008
    #6
  7. Paul B <> writes:

    > I am looking for some 1-to-1 matching transformers to connect varioua
    > audio devices to my PC. I usually get noises and hum.


    Here are some of my experiences on making mu own such devices:
    http://www.epanorama.net/documents/groundloop/audio_isolator_building.html

    > These line matching transformers are not so cheap at about £6 or 7
    > each.


    Good quality transformers seem to cost considerable amoutn of money.

    > Telephones seem to suppress line noise and hum rather well so I
    > figure the components they use are probably of half-decent quality.


    600 ohms 1-to-1 matching transformers are quite rare in telephones.
    Modern normal telephones are normally "floating" line powered
    devices where electronics connect directly to line. The whole
    small device is "floating" isolted from everythign else
    so that gives good balance.

    You can find 600 ohms 1-to-1 matching transformers most often
    on modems. And those are also in some telephones that use
    external power...

    > If I strip down some landline phones I 've got here, then will there
    > be a matching transformer in each one?


    Propably not any transformer in a modern phone at all.
    And in older ones where there was a transformer that is most
    propably not a type of transformer you are looking for
    (for details on transformers used at beginning of
    http://www.epanorama.net/documents/telecom/teleinterface.html
    document).

    > Or is their technology different now?


    Modern normal telephones are normally "floating" line powered
    devices where electronics connect directly to line.

    --
    Tomi Engdahl (http://www.iki.fi/then/)
    Take a look at my electronics web links and documents at
    http://www.epanorama.net/
     
    Tomi Holger Engdahl, Dec 29, 2008
    #7
  8. Paul B

    Al Guest

    "Floyd L. Davidson" <> wrote in message
    news:...
    > Archimedes' Lever <> wrote:
    >>On Sat, 27 Dec 2008 22:03:10 GMT, Paul B <> wrote:
    >>
    >>>
    >>>If I strip down some landline phones I 've got here, then will there
    >>>be a matching transformer in each one? Or is their technology
    >>>different now?

    >>
    >> It isn't a matching transformer. It is for isolation purposes, and
    >>yes, there is one in all phones that attach to Ma Bell.

    >
    > Actually it *is* a matching transformer (check out the
    > impedance of a telset transmitter). It also provides
    > isolation. It is also a "hybrid" transformer.
    >
    > Pretty typical multiple use design from Bell Labs at the
    > height of the good ol' days.
    >
    > --
    > Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
    > Ukpeagvik (Barrow, Alaska)


    A real hybrid uses 2 transformers to get the 2-4 wire.
    All sorts of fiddle designs around 1 generally low quality tansformer in a
    phone.
    I have spent years breaking derelict BT plant I have found for their quality
    transformers wheich were made to a spec rather than a budget.
    As another poster said Sowters are good as are Partridge and Jensen
    although I always hark back to the late Dr Sowters designs.
    Sowter are the makers of the transformers in the RS range..

    For decent phone signal for broadcast or even generl audio use I tend to
    pull a Sonifex out.
    For other use I tend to use A Telex/RTS 2-4 wire box.

    Regards

    Al
    ..
     
    Al, Dec 29, 2008
    #8
  9. Stuart <> writes:

    > In article <Xns9B81E055CF04D74C1H4@69.16.176.253>,
    > Paul B <> wrote:
    >
    > > If I strip down some landline phones I 've got here, then will there
    > > be a matching transformer in each one? Or is their technology
    > > different now?

    >
    > Even if there is (they used to use hybrids but I don't know these days)
    > the quality will be poor. They are only intended for voice.


    True.

    > For music you
    > require a much larger bandwidth and lower distortion characteristics.


    The transformers used on 56k modems and such perform considerably
    better than the old telephone transformers in both available
    badwidth and distortion characteristics
    http://www.epanorama.net/documents/groundloop/audio_isolator_building.html

    > Expect to pay at least £30-50 for something decent by Sowter or similar.
    > Ideally, you will also need to know the impendence of your sound card
    > input to match it properly, or assume it is high (it probably is) and
    > resistively terminate the transformer secondary.


    Line level audio input connectors on PC sound cards are high impedance
    inputs, typically around 10-47 kohm.

    Depending on the selected transformer a terminating resistor
    on transformer output might be needed or not.

    --
    Tomi Engdahl (http://www.iki.fi/then/)
    Take a look at my electronics web links and documents at
    http://www.epanorama.net/
     
    Tomi Holger Engdahl, Dec 29, 2008
    #9
  10. Paul B

    Phil Allison Guest

    "Tomi Holger Engdahl"

    > The transformers used on 56k modems and such perform considerably
    > better than the old telephone transformers in both available
    > badwidth and distortion characteristics
    > http://www.epanorama.net/documents/groundloop/audio_isolator_building.html



    ** Misleading shit.

    Wot the **** is " my test circuit " ????????


    > Line level audio input connectors on PC sound cards are high impedance
    > inputs, typically around 10-47 kohm.



    ** Unlike a 600 ohm tranny - fuckhead.



    > Depending on the selected transformer a terminating resistor
    > on transformer output might be needed or not.



    ** ROTFLMAO !!!

    Fucking Google Groper ....




    ..... Phil
     
    Phil Allison, Dec 29, 2008
    #10
  11. Paul B

    Eeyore Guest

    Paul B wrote:

    > Telephones seem to suppress line noise and hum rather well so I
    > figure the components they use are probably of half-decent quality.


    Not really. It's because the telephone system uses balanced (or
    differential) audio signals and your PC doesn't.

    Graham
     
    Eeyore, Dec 29, 2008
    #11
  12. Paul B

    Eeyore Guest

    "Floyd L. Davidson" wrote:

    > "Phil Allison" <> wrote:
    > >> Telephones seem to suppress line noise and hum rather well so I
    > >> figure the components they use are probably of half-decent quality.

    > >
    > >** Nonsense.
    > >
    > >Generally phones have no such transformer inside ( no need exists as a phone

    >
    > Historically they *all* had such a transformer, and even
    > today many of them do (it's cheap).


    Transformers are not cheap and I haven't ever seen a phone with one in, even
    going back 30+ years. There's simply no need.

    Graham
     
    Eeyore, Dec 29, 2008
    #12
  13. Paul B

    Eeyore Guest

    Stuart wrote:

    > Paul B <> wrote:
    >
    > > If I strip down some landline phones I 've got here, then will there
    > > be a matching transformer in each one? Or is their technology
    > > different now?

    >
    > Even if there is (they used to use hybrids but I don't know these days)
    > the quality will be poor. They are only intended for voice. For music you
    > require a much larger bandwidth and lower distortion characteristics.
    > Expect to pay at least £30-50 for something decent by Sowter or similar.
    > Ideally, you will also need to know the impendence of your sound card
    > input to match it properly, or assume it is high (it probably is) and
    > resistively terminate the transformer secondary.


    Cheaper to buy a decent sound card with balanced ins and outs (plus not on
    those GHASTLY 3.5mm jacks) and learn how to use them properly.

    Terratec do a moderately inexpensive one IIRC.

    Graham
     
    Eeyore, Dec 29, 2008
    #13
  14. Paul B

    Eeyore Guest

    Archimedes' Lever wrote:

    > Paul B <> wrote:
    > >
    > >If I strip down some landline phones I 've got here, then will there
    > >be a matching transformer in each one? Or is their technology
    > >different now?

    >
    > It isn't a matching transformer. It is for isolation purposes, and
    > yes, there is one in all phones that attach to Ma Bell.


    Backward Americans as usual ! ;~)

    Graham
     
    Eeyore, Dec 29, 2008
    #14
  15. Paul B

    Eeyore Guest

    Al wrote:

    > A real hybrid uses 2 transformers to get the 2-4 wire.


    Or a couple of op-amps suitably configured.

    Graham
     
    Eeyore, Dec 29, 2008
    #15
  16. Paul B

    Eeyore Guest

    Al wrote:

    > I have spent years breaking derelict BT plant I have found for their quality
    > transformers wheich were made to a spec rather than a budget.
    > As another poster said Sowters are good as are Partridge and Jensen
    > although I always hark back to the late Dr Sowters designs.
    > Sowter are the makers of the transformers in the RS range..


    Lundahl are the best audio transformers around IMHO.

    Graham
     
    Eeyore, Dec 29, 2008
    #16
  17. Paul B

    Salmon Egg Guest

    In article <>,
    Tomi Holger Engdahl <> wrote:

    > 600 ohms 1-to-1 matching transformers are quite rare in telephones.
    > Modern normal telephones are normally "floating" line powered
    > devices where electronics connect directly to line. The whole
    > small device is "floating" isolted from everythign else
    > so that gives good balance.


    I know of no situation where something specified as say a 150 ohms
    1-to-1 matching transformer would perform significantly different than
    something specified as a 600 ohms 1-to-1 matching transformer. This
    assumes that they both can support the same voltage over the same
    (telephone audio) bandwidth. Am I missing something?

    Bill

    --
    Private Profit; Public Poop! Avoid collateral windfall!
     
    Salmon Egg, Dec 29, 2008
    #17
  18. Paul B

    Salmon Egg Guest

    In article <>,
    "Phil Allison" <> wrote:

    > ** Unlike a 600 ohm tranny - fuckhead.


    You really know how to use the language of Shakespeare.

    Bill

    --
    Private Profit; Public Poop! Avoid collateral windfall!
     
    Salmon Egg, Dec 29, 2008
    #18
  19. On Mon, 29 Dec 2008 08:05:25 -0900, (Floyd L. Davidson)
    wrote:

    >Eeyore <> wrote:
    >>Archimedes' Lever wrote:
    >>
    >>> Paul B <> wrote:
    >>> >
    >>> >If I strip down some landline phones I 've got here, then will there
    >>> >be a matching transformer in each one? Or is their technology
    >>> >different now?
    >>>
    >>> It isn't a matching transformer. It is for isolation purposes, and
    >>> yes, there is one in all phones that attach to Ma Bell.

    >>
    >>Backward Americans as usual ! ;~)

    >
    >An ignorant statement, to say the least.
    >
    >As far as it being a matching transformer, the line
    >impedance varies typically from perhaps 100 Ohms all the
    >way up to perhaps 2000 Ohms... but you will not find
    >anything in a telset to adjust it to match. That's because
    >nobody cares if it is even close to matching the line
    >impedance.


    Which is why I stated its primary purpose as being that of isolation
     
    Archimedes' Lever, Dec 29, 2008
    #19
  20. Paul B

    Phil Allison Guest

    "Floyd L. Davidson"
    > Eeyore
    >>
    >>> Historically they *all* had such a transformer, and even
    >>> today many of them do (it's cheap).

    >>
    >>Transformers are not cheap and I haven't ever seen a phone with one in,
    >>even
    >>going back 30+ years. There's simply no need.
    >>

    >
    > Get a diagram of any given telset you wish that works
    > without active components (amplifiers), and you *will*
    > find a transformer.
    >
    > And trust me, they *are* cheap!
    >
    > Going back 30+ years, they *all* had transformers.



    ** But not the 1:1 matching/ isolating kind the OP asked about - dickhead.

    The " hybrid " circuit couples the earphone and mic to the line but is
    generally not even isolating.



    ....... Phil
     
    Phil Allison, Dec 29, 2008
    #20
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