Getting matching transformer from telephone

[Phil Allison]

"Stuart"

However, regardless of what you know or don't know, this thread was
started by someone who wanted to know whether he could re-use the
transformers in telephones for another purpose so clearly he has some!

** That is entirely false.

What the OP *actually asked* was this:

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

Chances are high there are no iron core transformers ( hybrid or other) in
his phones at all - cos they are too modern.

Secondly, his purpose requires a transformer with high voltage safety
isolation from the phone line - which the common 600:600 ohms phone line
types all have and others do not.

Thirdly, his purpose requires a transformer with very high CMRR - cos that
is why he is getting humming noises at the moment when making recordings
with his passive ( ie non-transformer ) adaptor device.

Have you ever done this ??

I can assure you it ain't as simple as you suspect to get a hum free and
distortion free result.

Not the least of the problems is that portable voice recorders have high
sensitivity mic inputs with automatic gain control circuits - which cannot
be defeated by the user. This results in annoying gain pumping and regular
bursts of overload distortion PLUS increasing background noise & hum
whenever there is a pause in the conversation.

The trick is to use just the right amount of resistive divider attenuation
before and after the 1:1 transformer to eliminate this - plus cap couple
the input side to stop pulling the line low.



..... Phil

 

[Stuart]

In article <495EA099.F27F1030@hotmail.com>,
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

I'm afraid I wasn't around in 1935. 73 yr old technology is somewhat
irrelevant.

Not irrelavant when we were discussing the history of why 600 ohms became
the standard impedance for audio distribution.

These days a phone is a chip and a few passives (that *aren't* big
inductors).

Modern phones don't use carbon mics either yet you claim

I have never seen a transformer in ANY phone including the carbon mic
type

Perhaps you'd prefer the inside of the ubiquitous BT 746 which was
introduced in 1967 and was around for a very long time - we didn't replace
ours till well into the 90s

http://www.telephonesuk.co.uk/images/746_cct.jpg

This is a 1978 version.

In 1985 it was fitted with the new style plug and became the 8746 but
still had the "Induction coil"

However, regardless of what you know or don't know, this thread was
started by someone who wanted to know whether he could re-use the
transformers in telephones for another purpose so clearly he has some!

--
Stuart Winsor

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

 

[Stuart]

In article <495EA761.BE86871E@hotmail.com>,
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

High-fidelity Microphone

" Common uses include matching the relatively low 2K ohm output
impedance of a microphone to an amplifier’s much higher line input
impedance of 10K ohms. Studios commonly use the three terminal “XLR”
type of connector which is a balanced connection method with a terminal
for a center tap. A separate ground terminal, tied to the XLR
connector’s case is almost always present. The center tap may be used to
phantom-feed a small amount of current for powering a pre-amp or active
“condenser” microphone."

LMAO !

You mean you didn't know that either?

Ok, a typical dynamic microphone is often nearer 150-300 ohms output
impedence and Ribbons can be as low as 50 Ohm but otherwise......

--
Stuart Winsor

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

 

[Phil Allison]

"Stuart"

Eeysore

High-fidelity Microphone

" Common uses include matching the relatively low 2K ohm output
impedance of a microphone to an amplifier's much higher line input
impedance of 10K ohms. Studios commonly use the three terminal "XLR"
type of connector which is a balanced connection method with a terminal
for a center tap. A separate ground terminal, tied to the XLR
connector's case is almost always present. The center tap may be used to
phantom-feed a small amount of current for powering a pre-amp or active
"condenser" microphone."

LMAO !

You mean you didn't know that either?

** The above para is full of technical howlers - as are many other
paras in the article

You have only spotted one of them.

Ok, a typical dynamic microphone is often nearer 150-300 ohms output
impedence and Ribbons can be as low as 50 Ohm but otherwise......

** The author has first confused the typical and recommended *load
impedance* of a mic input with the actual source Z of professional mics.
Then he confuses the line input Z of an amplifier with the input Z of a
transistor preamplifier circuit as found in ( old fashioned) mic inputs.

What he is * really * alluding to is that his company sells 2,000 ohm to
10,000 ohms transformers ( ie 1:5 ) for mic input use.

The stuff about studios using 3 pin XLRs with " centre tap" connections is
an absolute pig's breakfast !!

What the confused author seems to be alluding to is the ( now obsolete)
practice of using the centre tap on the 2,000 ohms winding of his company's
mic input transformers as a source point for 48 volt phantom power.

Fact is - XLRs used for mic inputs ALL have pin 1 as ground & cable
shield and use pins 2 and 3 for mic signal and phantom power.



...... Phil

 

[Archimedes' Lever]

On Sat, 3 Jan 2009 12:27:51 +1100, "Phil Allison"
<philallison@tpg.com.au> wrote:

What the OP *actually asked* was this:

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

Which, to anyone with even half a brain, obviously means that he wishes
to utilize it as well, you stupid fucktard!

 

[Phil Allison]

"Stuart"

However, regardless of what you know or don't know, this thread was
started by someone who wanted to know whether he could re-use the
transformers in telephones for another purpose so clearly he has some!

** That is entirely false.

What the OP *actually asked* was this:

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

Chances are high there are no iron core transformers ( hybrid or other) in
his phones at all - cos they are too modern.

Secondly, his purpose requires a transformer with high voltage safety
isolation from the phone line - which the common 600:600 ohms phone line
types all have and others do not.

Thirdly, his purpose requires a transformer with very high CMRR - cos that
is why he is getting humming noises at the moment when making recordings
with his passive ( ie non-transformer ) adaptor device.

Have you ever done this ??

I can assure you it ain't as simple as you suspect to get a hum free and
distortion free result.

Not the least of the problems is that portable voice recorders have high
sensitivity mic inputs with automatic gain control circuits - which cannot
be defeated by the user. This results in annoying gain pumping and regular
bursts of overload distortion PLUS increasing background noise & hum
whenever there is a pause in the conversation.

The trick is to use just the right amount of resistive divider attenuation
before and after the 1:1 transformer to eliminate this - plus cap couple
the input side to stop pulling the line low.




..... Phil

 

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
Twisted pair cables are not 600 Ohms.

Absolutely not. About 100 ohms.

Cable type Impedance at 1000 Hz

19NLS 470
19NLP 262
19H50P 675
16B22 806
19H245S 1882

What kind of screwy cables are those ? 1kHz has NOTHING to do with their
characteristic impedance.

Here we use CW1308.

And why the heck do you think ADSL is based around an assumption of
typical 100 ohm charactistic cable / line impedance ?
http://www.st.com/stonline/products/literature/an/7205.pdf

CRETIN !

Speaking of cretins!

The chart is from Bell System documentation (which I cited in
another article). If you think the frequency has nothing to do
with the characteristic impedance, argue with Bell Labs.

ADSL is based on 100 Ohm impedance for very good reasons. One
of them being the frequencies used...

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

 

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
"Floyd L. Davidson" wrote:

Telephone cable is twisted pair

Which is why it's 100 ohms or so just like Cat 5 etc.

Except of course when it has loading coils in it, and
then it is something much higher.

Try running ADSL down a line with loading coils ! There's no need for
them anymore. These days you just adjust the line gain.

Did you see where it said above... "Telephone cable".
Not all telephone cable can run ADSL. (And no you don't
"just adjust the line gain".)

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

 

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

Stuart wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

I have never seen a transformer in ANY phone including the carbon mic
type which also 'draws power from the line' to power the mic as you say.

How do the clowns think they determine ON and OFF HOOK ?

Graham

Oh dear, you need educating.

http://www.telephonesuk.co.uk/images/232_cct.jpg

What do you think "Coil,Induction No20" is?

I'm afraid I wasn't around in 1935. 73 yr old technology is somewhat
irrelevant.

The definition of on/off hook supervision has not changed, and that
makes it exceedingly relevant.

These days a phone is a chip and a few passives (that *aren't* big inductors).

Not necessarily. Some do have transformers.

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

 

[Floyd L. Davidson]

"Phil Allison" <philallison@tpg.com.au> wrote:

"Stuart"

However, regardless of what you know or don't know, this thread was
started by someone who wanted to know whether he could re-use the
transformers in telephones for another purpose so clearly he has some!

** That is entirely false.

What the OP *actually asked* was this:

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

Chances are high there are no iron core transformers ( hybrid or other) in
his phones at all - cos they are too modern.

Secondly, his purpose requires a transformer with high voltage safety
isolation from the phone line - which the common 600:600 ohms phone line
types all have and others do not.

Thirdly, his purpose requires a transformer with very high CMRR - cos that
is why he is getting humming noises at the moment when making recordings
with his passive ( ie non-transformer ) adaptor device.

Have you ever done this ??

I can assure you it ain't as simple as you suspect to get a hum free and
distortion free result.

BS. It is *very* simple. Every simple (or complex)
telephone for a hundred years or so has been doing the
exact same thing!

Not the least of the problems is that portable voice recorders have high
sensitivity mic inputs with automatic gain control circuits - which cannot
be defeated by the user. This results in annoying gain pumping and regular
bursts of overload distortion PLUS increasing background noise & hum
whenever there is a pause in the conversation.

And *you* don't know how to set levels properly to
handle that?

Most people do know...

The trick is to use just the right amount of resistive divider attenuation
before and after the 1:1 transformer to eliminate this - plus cap couple
the input side to stop pulling the line low.

Why not use a properly designed pad, with the correct
impedance? "Pulling the line low"???? Giggle snort,
cough and laugh...

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

 

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

"Floyd L. Davidson" wrote:

Then just exactly how do you think the transmitter got
power in those old phones?

OLD (and no longer used) is all you seem to know about.

You falsely claimed it was otherwise. Seems *you* are
the one with a lack of "know" about this topic.

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

 

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

Phil McKerracher wrote:

Bill Janssen wrote:

...the phone should be a reasonable match to the line to minimize
refections which bother the
users as echoes...

This is true - someone (not sure who, sorry) commented earlier that this
doesn't matter because the speed of light is so high, and that's true for
local calls but not for long distance ones.

Which go via optical fibre or microwave link, NOT cable any more.

That is true, but doesn't mean what you apparently think
it does.

A mismatch at the distant end will result in echo, and
if the distance (no matter whether it is traversed via
metallic cable, fiber, microwave or satellite) is far
enough to delay the echo long enough, it will be heard
as an echo by the near end user.

Typical local calls usually have a low echo return
delay, while long distance will be higher. However,
that is not always the case and I can demonstrate
examples of local calls that are routed over satellite
systems (meaning the echo delay is necessarily very
close to 400-500 milliseconds). Those calls require
echo cancellation, because even if the echo is 30 dB
down, it is still very annoying when there is that much
delay.

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

 

[Eeyore]

"Michael A. Terrell" wrote:

Eeyore wrote:
Ross Herbert wrote:

Since your PC is mains powered and it may not have the required isolation
between the mains side and the sound card input you can do your own thing using
an approved 600:600 transformer with 3kV isolation rating to interface the
telephone line to the sound card input.

He DOES NOT need a 600 ohm transformer since the input impedance of the sound card
is not 600 ohms <sigh> !

It's more likely to be in the tens of kilohms.

What he really wants is something like a 10k:10k 'line bridging' transformer. In
practice, using a '600 ohm' transformer will probably be ok, but being incorrectly
loaded will degrade the sound quality (freq resonse may be peaky etc).

An 'audio expert' would put a 600 ohm resistor across the secondary
to provide proper loading but no expects you to know that.

Which would doubly load the line silly.

What is required here is what was typically once called a bridging transformer. Audio
doesn't use signal transformers much these days except the tube nuts. Or, come to that,
an active 'balun' with AC coupling to keep the line DC out. 2 caps, 4 resistors, a
single op-amp and maybe even battery powered. Plus some protection diodes for good
measure. 48V is a bit iffy even after a cap.

Graham

 

[Eeyore]

"Floyd L. Davidson" wrote:

Not all telephone cable can run ADSL.

In civilised parts of the world with proper infrastructure it can.

Graham

 

[Eeyore]

"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
Stuart wrote:
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

I have never seen a transformer in ANY phone including the carbon mic
type which also 'draws power from the line' to power the mic as you say.

How do the clowns think they determine ON and OFF HOOK ?

Graham

Oh dear, you need educating.

http://www.telephonesuk.co.uk/images/232_cct.jpg

What do you think "Coil,Induction No20" is?

I'm afraid I wasn't around in 1935. 73 yr old technology is somewhat
irrelevant.

The definition of on/off hook supervision has not changed, and that
makes it exceedingly relevant.

These days a phone is a chip and a few passives (that *aren't* big inductors).

Not necessarily. Some do have transformers.

Such as ?

Graham

 

[Eeyore]

Stuart wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

I'm afraid I wasn't around in 1935. 73 yr old technology is somewhat
irrelevant.

Not irrelavant when we were discussing the history of why 600 ohms became
the standard impedance for audio distribution.

It isn't. Not for about 45 years.

Graham

 

[Archimedes' Lever]

On Sat, 03 Jan 2009 04:39:32 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

"Floyd L. Davidson" wrote:

Not all telephone cable can run ADSL.

In civilised parts of the world with proper infrastructure it can.

Graham

In the right situation, someone might actually consider you as credible
too. Just not in the reality that we all live in. We call it the real
world. In it, you and credibility do not homogenize together. That is
one water your oily ass won't mix with.

 

[Eeyore]

Phil Allison wrote:

plus cap couple the input side to stop pulling the line low.

Damn right ! Not ONE of these 'phone experts' has mentioned that.

Graham

 

[Archimedes' Lever]

On Sat, 03 Jan 2009 04:41:13 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
Stuart wrote:
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

I have never seen a transformer in ANY phone including the carbon mic
type which also 'draws power from the line' to power the mic as you say.

How do the clowns think they determine ON and OFF HOOK ?

Graham

Oh dear, you need educating.

http://www.telephonesuk.co.uk/images/232_cct.jpg

What do you think "Coil,Induction No20" is?

I'm afraid I wasn't around in 1935. 73 yr old technology is somewhat
irrelevant.

The definition of on/off hook supervision has not changed, and that
makes it exceedingly relevant.

These days a phone is a chip and a few passives (that *aren't* big inductors).

Not necessarily. Some do have transformers.

Such as ?

Is it really so goddamned hard to accept the fact that such items do
exist?

Probably just as hard it is to accept the fact that you are a self
denying, US hating retard.

 

[Eeyore]

Archimedes' Lever wrote:

"Phil Allison" <philallison@tpg.com.au> wrote:

What the OP *actually asked* was this:

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

Which, to anyone with even half a brain, obviously means that he wishes
to utilize it as well, you stupid fucktard!

He can only utilise it if it contains one OBVIOUSLY !

Graham