This mixer was constructed for Universal City Studios around 1973.  It has 101 amplifier cards by Spectra-Sonics, a limiter that is equivalent to the Spectra-Sonics 610, input transformers(A-9-J) by Triad, mix pots by Waters, and other high quality parts. There are 4 mic amps with separate outputs, and all 4 can be routed into the main mono mix output which has the limiter. A line input(input #5) can be switched on so that the unit can function as a standalone line in/out limiter with 4 mic pres completely separate. Phantom power is available separately for all 4 mic preamps. An EQ(HF shelf boost) is also on the main mono output. Originally built for location movie work, it has been upgraded for the modern production environment. Mic preamps feature 3 gain settings, a high pass filter and a mix pot which works on the direct outputs. Input channel features: gain set in 3 steps; low cut filter, 6 dB/octave, at 100 hz, -6,-10,-15 dB Mix/Level pot,controls the level to the mono out and direct out Off/On Switch-enables the channel to the mono mix. Direct out is always active. Power switch: Off, On, and momentary:shows 0VU when 24 volts present on the power supply input Line in On/Off Line input level pot Limiter release time 0=shortest 9+longest Limiter Slope control: at minimum setting(CWW) slope is maximum, i.e. limiting action. as this is rotated, the slope(ratio) becomes more and more gradual and the limiter actually becomes a compressor.  The Limiter is always active, but threshold can be raised(Making the limiter less and less effective) by increasing the output control Output Level: at around 3:00 setting, the limiter threshold will be about 0dB. 48V power on: enables the internal voltage converter. This is a high headroom power supply that will easily handle P48 mics. Phantom switches for 48volts on each channel. TRS master out: this is the mixer out, and can contain any or all of the 4 mic inputs and the line input. TRS channel outs: these are unbalanced outputs for each mic channel, post mix pot. Blue indicator light: Shows when line input is active Red pilot lamp: shows when 24 volt power is switched on. Left VU meter: Shows mono mix output level Right VU meter: Shows limiter gain réduction Red Knob: HF EQ. about 10 dB boost at 10khz, shelving curve.It has its own separate power supply with a 6 foot+ cable.This is a very unique and great sounding mixer!Here is a comment:Anything with Spectra Sonics inside is the best. And those trannies are so musical … never heard anything as sweet in last 25 years. Congrats on giving new life to a classic.Phillip Victor Bova,  Bova Sound, Ottawa, Canada(makers of the SAGE op amps)Search for the demo videos on UTube. Search"Spectra Sonics Mixer".