A Line-matching Transformer is an adapter with a female XLR connector on one end and a male 1/4” connector on the other. This transformer converts the low-impedance signal of a microphone to high-impedance for connecting to a device like JAM. In this process, the transformer is providing additional gain for optimal signal level.
Example: http://www.radioshack.com/product/index.jsp?productId=2062443
Also Called: Impedance Matcher, Impedance Transformer