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 £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?

 

[Franc Zabkar]

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

 

[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 £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

 

[Salmon Egg]

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

 

[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.

 

[Archimedes' Lever]

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.

 

[Tomi Holger Engdahl]

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.

 

[Al]

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.

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]

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.

 

[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 **** 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]

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]

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]

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]

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]

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

Or a couple of op-amps suitably configured.

Graham

 

[Eeyore]

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

 

[Salmon Egg]

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

 

[Salmon Egg]

** Unlike a 600 ohm tranny - fuckhead.

You really know how to use the language of Shakespeare.

Bill

 

[Archimedes' Lever]

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

 

[Phil Allison]

"Floyd L. Davidson"

Eeyore

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