MCL moving coil step-up transformer.  A very high quality unit for the best cartridges.  The turns ratio is 1:20, making this transformer ideal for low output moving coil cartridges with output voltages in the range 0.15mV to 0.3mV.  The core material is cobalt based uncut amorphous strip and the winding geometry helps reject hum.  The load impedance presented to the cartridge is 100 ohms and the bandwidth is 8Hz - 75kHz (10 ohm source impedance).
Transformers supplied by Lundahl.

further details here: http://www.rothwellaudioproducts.co.uk/html/mc_step-up_transformer.html