isolation transformer costs $45!!!!!!!!!!!

[vinodquilon]

I am planning to tap a telephone line through an isolation transformer 600Ω/600Ω of 1:1 type. In our local market it is not readily avail. After a lot of search I have found one Dax 56K DX-56PU modem from one electronic shop and they put forward $45 for modem. Actually I only want one small transformer inside it.

Find the attachment. Non-SMD Type transformer with white colored core. T1 AASUPREME.
I have heard there also exists modem line transformers with 600Ω primary and different secondary (600,330,560,etc) resistances. How can I fix this should be 600Ω/600Ω Type.

Does it is mandatory to use 600Ω/600Ω in Telephone tap......

Can I possible to take outs from transformer leads on underside of the PCB without desoldering the costly PCB board.

 

[Hero999]

Yes, you need an isolation transformer to comply with the safety regulations.

My local supplier sells 600R transformers, they start as £2.95 which is $4.61 (US).

**broken link removed**

 

[mneary]

If you are tapping a telephone line, the impedance has an effect on voice quality. But you should get good results if the transformer is any impedance between 600 and 2000 ohms. A ratio anywhere from 1:1 to 3:1 should work in most circuits.

WARNING: This assumes that you are not running any DC through the transformer.

 

[Hero999]

The DC can be removed by connecting a capacitor in series with the transformer's primary winding, 1µF will be enough to pass all frequencies down to 300Hz which is the lower cut-off for a phone line. This assumes that the transformer is connected to a 600R resistive load, otherwise the capacitance can resonate with the winding inductance.

 

[atferrari]

Salvaging one from a discarded modem, isn't an option?

 

[Sceadwian]

Or an ethernet based device? I don't know if they're suitable for telephone work but all Ethernet devices require isolation transformers.

 

[audioguru]

I think they still use dial-up modems in India. They are about 20 years behind us. Many people there don't have electricity unless they connect to it themselves and steal it.