Getting matching transformer from telephone

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?

On Sat, 27 Dec 2008 22:03:10 GMT, Paul B <(E-Mail Removed)> 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.

"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

In article <Xns9B81E055CF04D74C1H4@69.16.176.253>,
Paul B <(E-Mail Removed)> 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!

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

On Sat, 27 Dec 2008 22:03:10 GMT, Paul B <(E-Mail Removed)> 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.

Paul B <(E-Mail Removed)> 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/g..._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/t...interface.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/

"Floyd L. Davidson" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Archimedes' Lever <(E-Mail Removed)> wrote:
>>On Sat, 27 Dec 2008 22:03:10 GMT, Paul B <(E-Mail Removed)> 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) (E-Mail Removed)

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
..

Stuart <(E-Mail Removed)> writes:

> In article <Xns9B81E055CF04D74C1H4@69.16.176.253>,
> Paul B <(E-Mail Removed)> 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/g..._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"

> 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/g..._building.html


** Misleading ****.

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 - ****head.



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


** ROTFLMAO !!!

****ing Google Groper ....




..... Phil