Next question - re star ground. Does it have to be grounded to the case? Diagram shows symbol for ground coming off the star point - does this mean I need to attach an external true earth ground to this point? Does ground for 12V trigger need to go to star point as well?
Star ground means everything that needs to be grounded gets its own pathway to ground. Said differently, avoid daisy-chaining ground connections. The incoming neutral/ground from your power supply needs to be tied to the star ground. If your PS is a simple 2 wire 12 VDC supply from a wall-wart then just use the ground side of that incoming power - you don't have to run a separate true earth ground in that case. If your PS is a typical H-N-G 3 wire AC main going to rectifier/bridge/filter etc. then the G should go to the star ground. The 12V trigger ground also goes to star ground.
As to whether the case itself has to be grounded, I recommend it also be grounded. Some use the connection to case itself as the star ground point but I prefer some other dedicated star ground point. And if you happen to have a non-metallic case then of course it's a moot point.
Here's how we ground our finished preamps:
All these "grounds" have separate physical connections to single star ground point.
Incoming PS ground
LDR3x power ground
12 V Trigger ground
LDR3x or IO3 left channel ground
LDR3x or IO3 right channel ground
Left channel RCA jack ground (I do daisy chain multiple RCA signal grounds together)
Right channel RCA jack ground
Star grounding equals - No ground loops - No hum - No problem.
