The unit contains all the necessary features for a complex playback session with several different monitor mixes. All aux and cue sends and a matrix stereo of the surround master are available at the adding input selectors. Talkback is included and be selected and controlled independently.

An additional stereo source selector with 8 stereo inputs makes possible to expand the capacity of the control source selector.

The Headphone Sections
The sections are identical and three of these sections are included on every module. A mixing source selection matrix allows to add aux sends to a basic monitor mix. This feature makes it very easy to provide different monitor mixes with the favored setting for each musician and a basic mix can be arranged on the stereo cue send. The different versions for the particular musicians are generated by adding different aux sends to each mix. If the bass player needs to have a stentorian snare drum for e.g. aux 2 can be used to force the snare to his mix just by selecting this send in addition to cue. In most cases, the main surround mix can be used as basic for playback as well. The adding matrix has 7 inputs. PGM, the stereo downmix of the surround master, the CUE send and CTR, the matrix stereo of the selected control room source are stereo while AUX1 to AUX4 or mono. In normal operation mode, the aux sends are mixes to both the stereo channels. A jumper block per selector makes it possible to mix each aux send to the left or to right channel only.

An additional switch, CTR, disables the adder and connects the input of the playback section to the output of the control room downmix matrix. In this case, the headphone follow the control room select.

The Talkback section requires the additional Talkback / Oscillator Module. The STU (studio) switch of this module activates the common talkback line for all the sections of the STU units. Every section has a talkback level control and a TB-OFF switch, that disables the talkback system for this particular output. Talkback is mixed to the playback signal that is dimmed by 12 dB. The dim level is determined by 2 resistors and can be easily adapted.

The Mono matrix is a standard adding matrix with 6 dB attenuation that can be used to sum the playback out to mono. The volume is controlled by a rotary pot and the CUT switches mutes the output of the section.

The Output Amplifier of every headphone section can drive 3 to 6 headphones in parallel, depending on the impedance of the headphones. It is possible to drive 6 2000 ohm phones or at least 3 phones with resistors of 600 ohm or less. One output should be connected only to headphones of the same kind to avoid level differences. All the output are fully protected.

The Studio Speaker section.
The additional studio speaker section is based on the same principle. The difference of the studio speaker section is the the output circuit that is a balanced line driver unlike the headphone amplifier. In addition, there is a DIM function (20 dB) and an Autocut function. If Autocut is enabled, an internal or external control signal can mute the speakers automatically.

The Stereo Source Selector
8 additional stereo sources can be connected to the select switch block that is part of the module. The section uses a mechanical switch array with mutual release that is electrically interlocked. It is passive and switches the balanced stereo lines. The output of the selector is available on one of the stereo switches of the surround control room unit.