Getting matching transformer from telephone

[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 Ł6 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?

 

[Franc Zabkar]

On Sat, 27 Dec 2008 22:03:10 GMT, Paul B <mail@nomail.invalid> 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 Ł6 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.

 

[Phil Allison]

"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 Ł6 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

 

[Salmon Egg]

In article <Xns9B81E055CF04D74C1H4@69.16.176.253>,
Paul B <mail@nomail.invalid> 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 Ł6 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!

 

[Blah Blah Blah]

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

 

[Stuart]

In article <Xns9B81E055CF04D74C1H4@69.16.176.253>,
Paul B <mail@nomail.invalid> 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 Ł30-50 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.

--
Stuart Winsor

For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk

 

[Archimedes' Lever]

On Sat, 27 Dec 2008 22:03:10 GMT, Paul B <mail@nomail.invalid> 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.

 

[Floyd L. Davidson]

"Phil Allison" <philallison@tpg.com.au> 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).

is not grounded like your PC is ) and in any case they are not suitable for
hi-fi audio.

That is quite true. The transformer in a telephone is
usually referred to as a "network", and it probably
includes components other than just the transformer,
plus it is a balanced hybrid transformer (and the
network has an imbalance built in to provide sidetone)
designed to carry at least 120mA of loop current. Not
exactly what one would go for in a hi-fi system!

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[Floyd L. Davidson]

Archimedes' Lever <OneBigLever@InfiniteSeries.Org> wrote:

On Sat, 27 Dec 2008 22:03:10 GMT, Paul B <mail@nomail.invalid> 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) floyd@apaflo.com

 

[Tomi Holger Engdahl]

Paul B <mail@nomail.invalid> 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 Ł6 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/

 

[Al]

"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
news:87myegovou.fld@apaflo.com...

Archimedes' Lever <OneBigLever@InfiniteSeries.Org> wrote:
On Sat, 27 Dec 2008 22:03:10 GMT, Paul B <mail@nomail.invalid> 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) floyd@apaflo.com

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
..

 

[Tomi Holger Engdahl]

Stuart <Spambin@argonet.co.uk> writes:

In article <Xns9B81E055CF04D74C1H4@69.16.176.253>,
Paul B <mail@nomail.invalid> 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 Ł30-50 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/

 

[Phil Allison]

"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 fuck 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

 

[Eeyore]

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]

"Floyd L. Davidson" wrote:

"Phil Allison" <philallison@tpg.com.au> 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]

Stuart wrote:

Paul B <mail@nomail.invalid> 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 Ł30-50 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]

Archimedes' Lever wrote:

Paul B <mail@nomail.invalid> 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]

Al wrote:

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

Or a couple of op-amps suitably configured.

Graham

 

[Eeyore]

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

 

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

Al wrote:

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

Or a couple of op-amps suitably configured.

Or one transformer with three windings. Or, for that
matter, a network of resistors can make a nice hybrid too.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com