How can I tell if I have a serial loop?

[swill777]

I have an older black face rackmount dual rec... it has the loop send and return, with the send level, and mix return knobs... how can I tell if I have an earlier enough version that has a serial loop? were these knobs just not there?

 

[mikey383]

You have a parallel loop. The Rectos with serial loops won't have a mix knob.