Summing Mixer 1222



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User's Manual

The Iron Age Summing Mixer was designed to replicate the summing bus from a classic large format console: the end of the signal chain and the heart and soul of every mixer. The 1222 can be thought of as part of the routing matrix on a large format console. This means that there’s no right and wrong way to use it – any mixing, sub-grouping, and signal routing can be accomplished to suit your needs.  The unique dual stereo or stereo and dual mono outputs allows great flexibility with signal processing and routing, including parallel processing of a subgroup on a single box.  It also allows multiple stems to be created and routed, and provides a barbaric amount of routing flexibility in the analog domain.


The 1222 has 12 balanced transformerless inputs, each with individual pan controls onto a switchable stereo bus. In addition to the stereo bus, the 1222 has a second pair of switchable mono busses for mono or L-C-R panning.


Further, because the stereo bus and mono busses feature slightly different gain staging, a signal could be sent to both – in some applications you may prefer one or the other.


Each bus is summed using an active combining amplifier followed by an output transformer. The stereo bus has a nominal -2 dBu (6 dB below the output level at full fader) unbalanced insert point, similar to what is found on many classic large format consoles. This is followed by a master fader level control and an output line amplifier.As with all Iron Age modules, the Summing Mixer uses custom discrete operational amplifiers for all amplifier duties. The stereo bus features two gain stages, each with a carefully selected Cinemag output transformer to give your mix the warmth and heft that only iron can.

Block Diagram

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Technical Specifications

Input Impedance                           >10 kOhms, all inputs

Output Impedance                        <75 Ohms, transformer balanced

Maximum Input Level                    +20 dBu

Maximum Output Level                 +26 dBu

Gain (Input to any Bus output)      +0 dB (unity)

Frequency Response                    +0.1, -0.6 dB 20Hz-20kHz

Actual Measured Noise (any bus) -93 dBA

THD @ +15 dBu output                 


      Stereo bus                               0.003% typical

      A/B bus                                    0.0015%

Crosstalk (any bus to any bus)       Better than –60 dB

Power Consumption                       300 mA max

This product has been retired for now. If you are interested in owning one please contact us at: