The BMA-400 AC/DC Bioamplifier is a low-noise, four-channel instrument for amplifying EEG, ECG, EMG, and other extracellular biopotential signals. It features exceptionally low noise, a wide gain range, and sharp cutoff bandpass filters. It can be used as a stable DC amplifier, and includes adjustable DC input offset controls. The BMA-400 features a high-impedance instrumentation amplifier differential front-end, for the lowest noise and best rejection of spurious signals. Gain is adjustable from 10X - 50,000X, extensible to 500,000X with optional head-stages, making it possible to resolve microvolt level signals with ease. A special logic input allows a stimulus to be passed through the recording electrodes. This stim/record input, as well as the four channel outputs, are connected to a multi-pin connector on the rear panel for convenient cable connections. Four input connectors are provided for custom wiring of the inputs. Pre-wired cables are available as an option. Applications for the BMA-400 Bioamplifier include multi-channel EEG, EMG, and other extracellular biopotential measurements. For recording from human subjects, optional ISO-Z Isolation Amplifier head-stages are available. For high-impedance microelectrode work, the SUPER-Z head-stage is available, which provides a calibrator as well as additional gain and buffering.