Getting matching transformer from telephone

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No, you build monstrosities, then brag about them.
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On 30 Dec 2008 11:54:01 +0200, Tomi Holger Engdahl

I'd just like to contribute a couple of references which I found useful in the past.
This [old] document talks about complex impedances (see page 37): http://web.archive.org/web/20001001070243/http://www.midcom-inc.com/pdf/TN69.pdf
International Digital Access Arrangements: http://groups.google.com/group/comp.dcom.modems/msg/232247c06425cc1d?dmode=source
- Franc Zabkar
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Franc Zabkar wrote:

http://web.archive.org/web/20001001070243/http://www.midcom-inc.com/pdf/TN69.pdf
Some classsic audio howlers in there !
High-fidelity Microphone
" Common uses include matching the relatively low 2K ohm output impedance of a microphone to an amplifiers 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 connectors 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 !
The rest looks useful though.
Graham
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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......
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Stuart Winsor

For Barn dances and folk evenings in the Coventry and Warwickshire area
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"Stuart"

** The above para is full of technical howlers - as are many other paras in the article
You have only spotted one of them.

** 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
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Stuart wrote:

Rather different to 2k I think you'll agree.

Ribbons are FAR lower. Maybe 50 ohms AFTER the transformer !
And Pin 1 on an XLR is ALWAYS the cable shield. It may also be GROUND - but that's another story. It certainly isn't used to provide phantom power under ANY circumstances. And the last time I came across a centre tapped transformer in pro-audio was 35 years ago. It caused a bloody nuisance too. Modern balanced audio circuits are 'floating'. The centre tap provides ZERO advantage.
I now expect you to make an idiot of yourself trying to refute that one.
Graham
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but
under
Apart from providing the -return path- for the current sent over the balanced pair;)...
And the last time I came across a centre tapped transformer

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Tony Sayer


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tony sayer wrote:

Don't confuse him with facts. He has trouble breathing and typing at the same time.
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On Sat, 03 Jan 2009 07:26:23 -0500, "Michael A. Terrell"

Oh he can do that, albeit through the mouth. Because Dumb Donkey is a mouth breather, he drools as he types (loses control over other bodily functions, as well). The result is what you see here.
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krw wrote:

That's why he thinks its easy to fill potholes. Unfortunately, his fill is foul.
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We *were* talking about the impedance as presented to to the input of a mixer or whatever, i.e., yes, after the internal transformer, not the impedance of the ribbon itself. The once very widely used Reslo RB/L series was specified as 30-50 ohm

Did it suggest anything other than that in the given description?

It is always grounded, directly or indirectly, otherwise the screen fails to be effective.

So how does phantom power work then? You stick a voltage down the signal leads in parallel and the the return is via what?

If you were even born more than 35 years ago how come you know so little?
Why do you think people such as www.Lundahl.se and others are still manufacturing and selling them, even introducing new designs.
At a one-off price of around 20-30 quid they must be manufacturing them in "quantity"
R.S. Components are a hard-headed, very commercially minded electrical/electronics distributor, who only stock stuff they can shift in quantity, yet they still list a centre-tapped primary, microphone transformer
In an article in Electronics World April 1991, Douglas Self of Soundcraft stated "It is now rare to use input transformers...." It is clear, therefore, that they were still being used, even if only in specialist applications. That is a bare 18 years ago.
--
Stuart Winsor

For Barn dances and folk evenings in the Coventry and Warwickshire area
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One signal lead is connected to positive the other signal lead is connected to negative. Much the same way as telephones are powered. For screening to work it must not be carrying an electrical current.
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In the context presented, that is generally true... but I'd like to point out that the shielding on multipair telephone cables is 1) grounded, 2) commonly conducts current, and 3) the noise reduction provided is *enhanced* by the current!
Both ends of the cable are well grounded and any induced current in the shield will be greater than in any individual cable pair. The current in the shield induces an opposite current into the cable pair, thus reducing the total noise signal in each pair.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@apaflo.com
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Do you manage to get grounds in that soil over there, seemed to think it was more permafrost;)..
Those pix on the Floyd website look rather, well "cool" :)...
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Tony Sayer



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tony sayer wrote:

Try driving a 60 foot ground rod through permafrost some time.
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The OPs problem can be solved by using the circuit from p62 of Elektor magazine March 2006, "Telephone evesdropper". You should be able to obtain a copy via their website: www.elektor-electronics.co.uk
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Paul B wrote:

Not really. It's because the telephone system uses balanced (or differential) audio signals and your PC doesn't.
Graham
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Trollschemedes' }:) you slay me Roy.
Cuwahahahhahahahahaha !
coqu coqu
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pleeeez Trollschemedes' stop trying to tell roy anythin about faith and the soul or even life, you are not among da living - its stuff you don't kno anything about.....
Troll dont you get it? eres un Evil Phantasm.
coqu coqu
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On Mon, 29 Dec 2008 18:03:23 -0500, snipped-for-privacy@webtv.net (Roy) wrote:

That you are going to continue to troll the group with your pathetic, off topic horseshit?
We already knew you were about that. Face it, Roy... You're nothing more than an attention seeking PUSSY.
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