Getting matching transformer from telephone



Umm... beg to differ .. they are used for 2 and 4 wire analogue or analogue over digital voice band private circuits...
And they do sometimes use DC blocks but rarely now as point to point DC available paths are rather rare unless on the same ends of the serving exchange..;)...
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Tony Sayer



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tony sayer wrote:

I thought we were talking POTS ?
Graham
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Yeah .. sounds abaht right;-))...
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Tony Sayer


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"Archimedes'= SCHIZOPHRENIC LUNATIC TROLL"
** Go DROP DEAD !!
you VILE TROLLING PIECE OF AUTISTIC SHIT
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"Floyd L. Davidson" wrote:

Is that how long you've been practicing telephony ?
Graham
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"Floyd L. Davidson" wrote:

"Howls of derisive laughter" Bruce:
Graham
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Eeyore wrote:

That is a sign of dementia.
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On Sat, 03 Jan 2009 11:05:01 -0500, "Michael A. Terrell"

Or rabies.
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So you admit you cannot support your claims.
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Floyd L. Davidson <http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@apaflo.com
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"Floyd L. Davidson" wrote:

He can't even support his three chins.
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Phil Allison wrote:

Damn right ! Not ONE of these 'phone experts' has mentioned that.
Graham
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BS. I had previously discussed it in detail.
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Floyd L. Davidson <http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@apaflo.com
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"Floyd L. Davidson" wrote:

You are full of BS.
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Hi Phil and others. I am the original poster. Thank you to everyone who has kindly contributed to this discussion.
Please don't overlook some details I posted at: http://groups.google.com/group/uk.telecom/msg/4513d4edcdc47c3e
You are quite right about high sensitivity mic inputs and automatic gain controls. As you can imagine, when the phone's handset is picked up and used, the mic input is faced with something approaching line levels and I get severe overload of my recorder. Then when it goes quiet, the AGC kicks in. It's as you describe.
I have tried to "listen through" any such automatic gain as best as I could and I feel there is still detect much more hum than I would expect on the line.
In truth, I really need a more suitable flash recorder but they are harder to find than I expected.
Currently I use the Olympus WS-331M. <http://www.olympus.co.uk/consumer/2581_WS-331M.htm
Cost is important to me so I don't want to fork out for a digital field recorder like this low-end one especially as some reviews have not been kind to it. <http://www.dv247.com/invt/41901/ .
Prices in the flash-memory recorder market are tumbling such that now personal video recorders (like the Archos AV400) are about the same price and offer some additional very useful function. Although i don't know if that sort of model has suitable input and output sockets.
On the other hand, I don't want some MP3 player with a recorder thrown in as an afterthought because ones I have seen can have surprisingly limited bit rates and low quality. Anyway, many probably don't have a line level input, so I will once again most likely get problems with a mic input and AGC.
I take your (and other posters') points about a phone probably not having a suitable transformer. My headache from trying to make sense of some of the more technical aspects in this thread suggests it might be easier in the end to go and buy some 600:600 transformers.
I'm not too clear about this "CMRR" you mention. I know next to nothing about "common mode rejection ratio" although I did come across the concept when looking at balanced inputs with chunky XLR connectors. I googled it and got the following PDF but in the end I couldn't really understand anything in it about CMRR. Do I really need to consider CMRR if I am going to be making a recording from a phone line?
<http://www.jensentransformers.com/an/Audio%20Transformers % 20Chapter.pdf>
One new line of thinking I would like to bounce off you and the other kind contributors to this thread is whether it is possible in my case to use a simple mixer (like those a pop group might use). If I can avoid those 3-wire balanced inputs on such a mixer and use just the 2-wire inputs then would the mixer's op amps and other electronics have a suitable isolating effect? The price of such a mixer seems very competitive. I am thinking of a unit similar to this one:
Behringer XENYX 502 (32) http://www.dv247.com/invt/31558 /
In turn, that leads me to consider if I should attempt to get a separate a analogue-to-digital converter which goes into the PC via the USB. That way I hope to eliminate earth loop hum and other spurious noises which I mentioned in my first post.
Maybe something like the Behringer UCA202 for 20 http://www.dv247.com/invt/32730/? To be honest I have no idea if this would work but it seems to be good value.
I'm sorry to be darting about with various options but I didn't know it was going to be so complicated!
Any views and useful info from anyone would be most welcome.
Andy.
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I'm afraid there seem to be plenty of people around here who's sole pleasure in life is to hurl abuse and insults at anyone and everyone.
Even the remotest thing they seem to take a dislike to, or disagree with, for whatever reason, provokes a torrent of foul language with no reasoned or sensible argument.
I'm afraid a very thick skin is needed round here.
I am quite sure you have good and honest reasons why you wish to record telephone conversations. Some years ago when doing research into my family history I conducted a number of "interviews" with my father over the phone and these were recorded onto tape using the telephone answering machine, which had a recording facility, that we had at the time.
A while ago when receiving abuse from one of these cold calling telephone sales people, from ADT as it happens, I wished I had had telephone recording that I could have passed on to the police.
The best advice I can give is to read and filter out the useful advice and ignore everything else.
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Stuart Winsor

For Barn dances and folk evenings in the Coventry and Warwickshire area
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Paul B wrote:

Phil is a mental defective who doesn't take his medication. It doesn't take anything for him to freak out. Just ignore him, or even better just kill file him so you aren't tempted to reply to him. It just makes him behave even worse.
So much for 'National Health Care' down under. :(
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Stuart wrote:

It isn't. Not for about 45 years.
Graham
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45 years ago it certainly was!
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Stuart Winsor

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Stuart wrote:

Minority use even then.
Try and think WHY.
Graham
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Well, lets see now.
Because Graham doesn't like being proved wrong?
Because I didn't spend 20 or more years of my life measuring and testing audio systems, equipment and GPO lines that were all designed for 600 ohm characteristic impedance (among other things)?
Because until the 1980s (I think it was) The GPO/BT didn't have a monopoly on telecommunications, including the distribution of audio down its many miles of cable? [1] Minority use?
Because the BBC didn't have a number of large and small studio complexes where 600 ohms was the norm (Not anymore but it was then) for audio?
Because even the most modern audio test equipment doesn't have facilities for measuring 600 ohm systems? - Oh dear, another wrong answer.
Because this isn't a binary group and I don't have a website on which post proof positive that you are wrong but would you would ignore anyway?
However, let me try this quote on you. From "Studio engineering for Sound Broadcasting" - Iliffe - 1955 (that's about 45 years ago) p20: "The chain incorporates a Post office line and to avoid confusion.......In the early days most Post office lines were open wire lines and all these had an impedence of about 600 ohms"
Stuart
[1] Remember, we were discussing the history of why 600 ohms became the standard impedance for *audio distribution*. Not teleprinters, telegraph systems or even telephone wiring; or why the microphone input of a mixer desk is around 2k ohms.
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Stuart Winsor

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