A CLASS-A unit that can receive signals from various sources (mostly audio devices generating a 0 dBV line signal) including effects units, CD players, tape or digital recorders, preamps and electronic instruments such as keyboards or MIDI devices. Input section: The unit has two (left and right) fully balanced input connectors, which use space-saving stereo phone plugs. Connecting an unbalanced music signal, e.g. from a keyboard, via a simple guitar jack, is also possible. An unbalanced signal from a HiFi device such as a CD player can also be connected using two RCA connecters. Although the stereo line input unit is intended for nominal line level signals, the input amp’s sensitivity can be adjusted, from -12 dB to +25 dB, using the GAIN knobs. Left and right channels can be separately adjusted. Depressing the UNITY button sets the gain to 1, allowing the signal to pass (without amplification or attenuation) independently from the Gain knob setting. LOW and HIGH Filters: Line signals don't usually need strong shaping, but some small correction of higher and lower frequencies can be useful. Both channels are affected simultaneously. The CHANNEL ON button connects or disconnects the output routing for all outputs (AUX 1, AUX 2, AUX 3 and L/R), except the PFL routing. Similar to the MUTE button on other mixers, its functionality is however reversed: When the CHANNEL ON button is depressed, all outputs are connected. Also, whereas a MUTE normally only disconnects the L/R routing (the channel's fader), this unit's CHANNEL ON button affects all outputs. The AUX SENDS include three knobs for the left level control of each send (AUX 1, AUX 2, AUX 3) and three knobs for the right level control. Each single AUX send can therefore be controlled independently. Every AUX send can also "read" the signal pre or post fade, through the use of switch buttons. If a button is not depressed (orange light), the signal arrives "post fade", i.e. while the relevant auxiliary level is controlled by its level knob, the final outcome is also influenced by the channel fader's position. If a button is depressed (blue light), the signal arrives "pre fade" and is sent to the AUX master without being affected by the channel fader's position or movement. Note: To benefit from all the AUX sends (and other additional options), a MASTER AUX unit is required as well as the MASTER L/R unit. The MASTER L/R unit only receives AUX 1 and is intended for a basic configuration, e.g. when only one auxiliary send is needed to operate a reverb device and no stage monitors are being used. The MASTER AUX unit also offers a CLASS-A headphone output, talkback function and Room output to control the studio monitors. MONO and PFL: Depressing the MONO button sets the unit's stereo configuration to mono, i.e. the two L and R channels are mixed together. Useful when listening to a stereo program reproduced in mono, in order to evaluate its "mono compatibility". Depressing the mono switch connects the single signal to both the L and R faders so that the music appears on both channels (depending on the setting of the L and R faders). When used on a single mono BUS, the PFL sends the L and R from the stereo input unit as a mono signal to the phones, or PFL output on the AUX master unit. As well as being a traditional PFL (pre fade listen), it also serves as a fourth AUX send (without the possibility to set any level). Signals from any channels with an activated PFL (red light) will be mixed in the MASTER AUX unit and sent to the PFL output, controlled by the PFL fader on the master AUX unit. Note: The PFL section still runs if the CHANNEL ON button is deactivated (white light). L / R FADER section. In most cases, the signal going through here will be mixed in the L/R Master before appearing on the main L/R outputs that drive the recording device or the front-of-house PA speakers. Operating the L/R fader section is the same as on other mixing consoles. The PAN pot enables signal to be sent to the Left or Right channel by turning it in the appropriate direction. At the pot's mid position, the signal flows to both channels at maximum level.