Wisdom in mind,   enthusiasm at heart.

Master-3A (50W Pure Class A)

Each channel has 90W @ 8 ohms ,360W @ 2 ohms max power
Real Balanced ACSS Non Negative Feedback Power Amp
Supports XLR and ACSS inputs
Applied "Linear Fidelity" Technology
Soft Start Power Design
24 pcs output transistors
　

How to connect the preamp only had the RCA output :
      Master-3 is a real balanced design power amp, so even connect the RCA output from preamp, can conversion to balanced output in the amp inside ,without any extra circuit board .
     While connect to the RCA output preamp, we are advice applied the RCA to XLR cable as below diagram . This is can be better than use the RCA- XLR adaptor and modify the Master 3 had RCA input sockets .