Serge dual 4:1 audio mixer 

ARC’s Serge Audio Mixer (SAM) is an officially licensed eurorack implementation of the original mixer module designed by Serge Tcherepnin for his Serge Modular Music System in the 1970s.  It features two independent 4:1 mixer submodules.

The SAM module is available in two versions with slightly differing electronics. The SAM MC version is built using LM741 (metal can) op-amps. The SAM RC is built with an RC4136 quad op-amp. The output of the MC version is 180 degrees shifted from the input. This can lead to phase cancellation in some applications. The RC versions uses an additional op-amp stage to shift the output another 180 degrees, keeping the inputs and output in phase. Historically the LM741 was the original Serge mixer op-amp, later redesigned to use an RC4136 to address potential phase cancellation.