Is there a transformer that....

[madriaanse]

can take the speaker signal from a (corded) phone handset and transform it to mic-level? (I need to record some web-conferences, using the phone for audio)

THX!!

M.

 

[emrr]

You need a phone hybrid set.  Gentner is one manufacturer.  Lots on the used market, I'm sure.  I have done a fair number of corporate meetings that involved a phone patch, and there is a well established standard.

 

[PRR]

I'll assume you want (or can accept) getting BOTH ends of the conversation. Otherwise you do need a hybrid to separate east from west.

Bridge the line with a 10K:600 line transformer, DC-blocked with a 1.0uFd 200V film cap.

If you do not block the DC, the phone line never hangs-up; also line-powered phones starve.

At this ratio, the output (at 600r) is very-very hot for "mike" inputs; tho maybe no hotter than a rock drummer or a Fender Twin. Expect to pad as needed.

FWIW: a tube power-amp OT will also work. 8K:8 is 30:1 voltage ratio. 100mV on line is 3mV at "8r" winding. And you know the OT won't overload. 

There ARE rules about this stuff.

Telcos have specs for what may be connected to their lines; thanks to Carterfone, they can't refuse a spec-compliant tap, but I make no claim that the above schemes meet all the specs. Personally, I doubt they can tell the difference.

There are federal and state laws about recording telephone conversations. IANAL.

 

[CJ]

i know we have threaded this subject before,
as always the question is, "where?"

does rat shack make a 9 dollar chinese device for this?


too late!

 

[madriaanse]

I should specify: this is on a digital Nortel sytem, so it looks like I'll be stuck tapping the speaker in the handset, no? I just need to record the person (the instructor) on the other end as these are web training seminars.

Thx!!

M.

 

[CJ]

ok, i got it:

http://www.spyworld.com/equipment/exec/search.cgi?search=1&perpage=20&lfield8_keyword=Telephone+And+Spy+Recorders&template=_search_results.html

 

[audiox]

Connect almost any audio/telephone transformer in parallel with the handset speaker. Output level is something like -15 dBu with 1:1 trafo, so it is better to use the line input of your mixer or make a pad.

Handset connector pinout:
http://en.wikipedia.org/wiki/4P4C

 

[burdij]

On my Nortel Meridian desk phone there is a jack labelled "#2" which, according to the manual, is a place where you can attach an analog device like a modem, fax machine, etc. You might try using the suggested circuit from PRR on that jack.

 

[ppa]

With phone sources a transfomer is needed because it's required for law and to elimitate noise, moreover it's necessary to use a cap to avoid the DC current, two diodes to limiting the DC transients.
If the mic preamp's input is balanced using a transfomer you can avoid the transfomer but adding 3 res to
reduce the audio signal level (plus the cap and the diodes).
The 3 resistors are used for making a balanced attenuator, isn't use a traditional 2 res att. to avoid to sbalanced the phone line to reduce the induced noise.
Soon a schematic

Pier Paolo

 

[hobiesound]

i recently made an installation in a ghosthouse. and i used a simple art transformer isolation box and a 3.3uF Wima to block dc and it worked perfectly. Very easy.

greetings,

Thomas

 

[ppa]

this is a scheatic to connect an trasformer coupled pre mic, c1 and c2 should be no polarized, R2 can be a trimmer of 200 ohm plus a resistors of 68 ohm to set attenuation.
This simple schematic goes with input trasformer only , not for input trasformerless preamp.