How Many Preamps Does Your Rig Need?

A preamp brings a microphone’s tiny signal up to the level the mixer works with. Every mic, and most DI boxes, needs one. Run out of preamps and the next input has nowhere to go.

Count your inputs

Write down every source that reaches the console, one line each. Our stage plot and input list guide shows the format.

1. Microphones: each vocal, each drum mic, each amp mic. A typical kit alone can take 6 to 10.
2. DI boxes: bass, keys (two for stereo), acoustic guitar. These land on preamps too.
3. Playback: tracks and click from an interface. These are line level and can use line inputs instead of preamps.
4. Wireless receivers: one input per channel unless they arrive over Dante.
5. Ambient mics for IEMs: usually a stereo pair. See ambient mics for IEMs.

Add two or three spare inputs. Bands add a guest vocal or a second keyboard more often than they remove a mic.

Where the preamps come from

• The console itself: 16 on an XR18 or X32 Rack, 24 on a Wing Rack.
• A stage box: 16 more per S16, SD16, AB168 or DX168, or 32 per DL32. See stage boxes for IEM rigs.
• An ADAT preamp expander on an audio interface: common in playback rigs, where an eight-preamp unit feeds the interface’s optical input. Check that your interface has an ADAT input before planning on it.

Preamp details that change the plan

• Combo jacks: an XLR/TRS combo input is one preamp, not two. Plugging in a line source uses it up.
• Phantom power: condenser mics and active DI boxes need 48V. Most digital consoles and stage boxes switch it per input; check whether yours switches in banks before mixing condensers with ribbon mics.
• Gain range and maximum input: matter for very quiet sources and very loud ones. Many quick start guides don’t publish gain range. The DX168 does (+5 to +60 dB), and the X32 Rack lists a +23 dBu maximum input.
• Remote gain: on digital consoles and stage boxes, gain is stored with the show file, so a festival changeover keeps your settings.

A worked example

A five-piece with drums (8 mics), bass DI, two keyboard DIs, two guitar amp mics, four vocals, a stereo ambient pair and stereo tracks: 8 + 1 + 2 + 2 + 4 + 2 = 19 preamp inputs, plus 2 line inputs for tracks. That is more than an XR18 or X32 Rack has locally. An X32 Rack with an S16 gives 32 preamps; a Wing Rack covers it with its own 24.

Lay the console and stage boxes out in the planner to see every input port in one place.

Sources

• Behringer XR18 listing: 16 Midas preamps, 48 V per input
• Behringer X32 Rack quick start guide, specifications: 16 mic preamps, +23 dBu maximum input
• Behringer WING RACK product page: 24 Midas PRO preamps, 48 V per input
• Behringer S16 product page: 16 preamps, 48 V per input
• Allen & Heath DX168 datasheet: 16 inputs, +5 to +60 dB gain, 48 V per input
• Midas DL32 listing: 32 inputs, 16 outputs