An EI audio transformer is a type of transformer commonly used in audio equipment such as amplifiers and audio signal processing devices. It is named after its core shape, which resembles the letter "E" and "I" when viewed from different angles. The EI transformer consists of two separate "E" shaped cores, which are made of laminated iron or steel sheets. These cores are stacked together with a small gap in between, allowing them to be magnetically coupled. The windings (coils) of wire are wrapped around the legs of the "E" cores to create primary and secondary windings. The primary winding is connected to the input signal, while the secondary winding is connected to the output. When an alternating current (AC) signal is applied to the primary winding, it creates a magnetic field that induces a voltage in the secondary winding, which is then used to drive the audio signal. The design of the EI transformer helps to reduce electromagnetic interference (EMI) and improve the overall performance of the audio equipment. The laminated core construction reduces eddy current losses and provides better magnetic coupling between the windings. This results in improved signal transfer and reduced distortion.