The basic concept of a current transformer is to measure large currents. So a typical current transformer will be like a doughnut (toroid) where the large current carrying conductor passes through the centre and the toroid core is wound with 500 turns of wire, such a transformer would be designed so that 1000A flowing through the centre conductor would induce a 5A current through its winding, which in turn would then be measured by a 5A AC ammeter which would drop 100 mV across its terminals at the full 5A, calibrated to read 0-1000Amps.
So note, a current transformer MUST be loaded with a low resistance and is rated at a low voltage out. So the above transformer, if it was used to feed a high impedance digital circuit, must have a resistor of 2 mOhms or at least very low , perhaps 1 ohm. if you did not have this low value load, on switch on, the voltage coming out of the transformer would be very high and could damage amplifier circuit.
If you have designed the transformer your self, you have to think about the secondary impedance being reflected back into the primary circuit which would add series inductance and resistance to it (which might upset it).
Frank