Unknown Transformer----details required

Discussion in 'General Electronics Chat' started by vinodquilon, Feb 12, 2010.

  1. vinodquilon

    Thread Starter Member

    Dec 24, 2009
    I am planning to tap a telephone line (to feed DTMF decoder as shown in the attachment) 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 contains one Transformer .

    Find the attachment T1 AASUPREME.
    For using that Transformer I have to know the following details.
    How can I know the following 4 specifications of the transformer,
    Impedance matching (intended value is 600 ohms to 600 ohms)
    Frequency response (intended value is 300-3400Hz for Plain Old Telephone System)
    Turns ratio (intended value is 1:1)
    Does it pass DC current through windings (otherwise I have to use separate capacitors at primary to block DC)

    Complete Transformer specification-
    aasupreme by
    C US 0514

    I cannot get the specifications through internet.
  2. SgtWookie


    Jul 17, 2007
    AASupreme is the modem, not the transformer.
    It's going to be a 1:1 600 Ohm transformer.
    I don't know why you can't find one locally.
    Have you tried RS Components or Farnell or Maplin?

    I have no clue which suppliers you have in India.
  3. ifixit

    AAC Fanatic!

    Nov 20, 2008
    Usually "Tapping" a phone line means to connect onto it without being detected and not causing the line interface unit to go into "off-hook mode. In this case you should not draw any DC current with your circuit and the AC load should kept above 10KΩ.

    Unauthorized phone tapping is usually illegal.

    If you actually do want to go off-hook then the DC current will pass through the transformer primary winding. Depending on the transformer design, this may work fine and not saturate the transformer. The current should be limited to around 20mA DC. The AC load is approximately 600Ω.