How to Connect Mics, Amplifiers, and Effects Units to Your Harmonica

Vocal mics and sound systems are made to work together, but harmonica players often use equipment that isn’t designed to work with modern sound systems. For instance, they often use archaic bullet mics as well as amplifiers and special effects units that are designed to work with electric guitars.

To make all this stuff work together, a harmonica player has to match up the different types of physical connecters and also match an electrical value called impedance. Impedance is measured in ohms (sometimes represented by the symbol Ω). If the impedances of two connected devices don’t match, the sound may be weak, thin, or muffled.

Connectors are wired onto the ends of cables and can be either 1/4 -inch phone plugs that plug into phone jacks or 3-pin XLR connectors (either male or female; male plugs into female).

Credit: Photograph by Anne Hamersky

Keep the following information in mind when connecting and matching impedances for the equipment that you use to amplify your harmonicas:

• Vocal mics, sound systems, and devices that connect with them use XLR connectors. Most are low impedance (or lo-z) and are measured in hundreds of ohms.

• Guitar amplifiers and guitar effects units use phone plugs and jacks and are high impedance (or hi-z), with impedances of anywhere from 1,000 ohms (a kilohm) to about 1 million ohms (or 1 megohm).

  When you connect a vocal mic to an effects unit or a guitar amplifier, you need a matching transformer to convert the low impedance of the mic to the high impedance of the guitar input. Matching transformers are small and come handily wired to an XLR connector on one end and a phone plug on the other.

  If you run your mic through a guitar effects unit and then to the house sound system, you need a direct box (sometimes called a DI box) to match the two impedances and connector types.

• Bullet mics are extra-high impedance (around 5 megohms), even though they typically use guitar-compatible phone plugs. A bullet mic may need a matching transformer to connect with guitar equipment. (To find out for sure, you’ll have to experiment.) A bullet mic definitely needs a direct box to go through a sound system.