Alto PBM4 Owner's Manual page 13

Strain Clamp
2 Hot(+)
Use for Balanced Mic Inputs
(For unbalanced use, connect pin 1 to 3)
3 pin XLR Male Plug
(seen from soldering side)
MAIN SPEAKERS CONNECTION
Please use only the power connectors to make connections with other signal
source equipment for the passive speaker cabinets. The power connector has
four terminals: 1+, 1-, 2+, 2-.
11
5. INSTALLATION AND CONNECTION
Sleeve
1/4" Stereo (TRS) Jack Plug
2
1
1 Ground/Screen
3
3 Cold(-)
Ring Return Signal
Tip
Ring
Sleeve Ground/Screen
Use for Insert Points
2 Hot(+)
(For unbalanced use, leave pin3 unconnected)
1+
2+
Speakon connector
Tip Send Signal
2
1
1 Ground/Screen
3
3 Cold(-)
Use for Main output
3 pin XLR Line Socket
(seen from soldering side)