Add a reverb effect unit to your hardware mixing console's "Return" channel. Plug one end of a 1/4-inch instrument cable into the "FX Send Output" jack on your mixing console and the other end into the reverb effect unit's "Input" jack. Plug one end of another 1/4-inch instrument cable into the "FX Return Input" jack on the mixing console, and the other end into the reverb effect processor's "Output" jack. Alternatively, add an instance of a reverb plug-in to your digital recording software's "Return" channel instead.
Turn the "Send" knob to its highest setting on each of the mixer channels you want to send to the reverb effect loop. This sends maximum signal from both the mixing console or digital recording software's individual tracks to the grouped reverb effect on the "Return" channel.
Set the reverb effect unit or VST plug-in's "Input Level" to the point where its clip indicator light blinks upon sending your instrument's most intense signal. Turn the "Send" level down on each channel to reduce the number of clip indicator blinks if your equipment has one, or to the level that sounds the best without distortion.
Turn the "Return" level knob down halfway, and then reduce the reverb effect unit's or VST plugin's "Output" level to the same level it was without the effect being applied. Use the level output meters on the mixer, or the digital recording software mixer screen section, as a guide for how high or low the "Output" level should be set to match the non-affected levels.