TREX and TREX2 Transistor regulator kit

[willgmr]

I’m using the TREX and a 48v SMPS to power 2x TAB 376a preamps. Would it be advisable to add a resistor in series and capacitor in parallel before running the raw SMPS 48V to pin 13 of the preamp (these have built in 6.81k phantom resistors)?

Thanks!

[Joe Malone]

I’m using the TREX and a 48v SMPS to power 2x TAB 376a preamps. Would it be advisable to add a resistor in series and capacitor in parallel before running the raw SMPS 48V to pin 13 of the preamp (these have built in 6.81k phantom resistors)?

Thanks!

HI Yes always a good idea to add 100R to 470R series resistor and 10uF to 100uF smoothing cap as it will remove any noise and isolate the phantom power better and provide soft start phantom on and off to minimize pops.

If wiring a phantom on/off switch use SPDT with SMPS 48v on one end and 0v on the other and centre of switch going to RC filter.

[willgmr]

Thanks, attached is what I understood you to suggest, but would that shunt Pin 13 to ground through the 100R resistor in the “Off” position?

Also, if I wanted one switch to switch phantom on for both preamps, am I okay to use one RC circuit for both or should I duplicate the RC circuit after the switch?

Thanks!

[Joe Malone]

Thanks, attached is what I understood you to suggest, but would that shunt Pin 13 to ground through the 100R resistor in the “Off” position?

Also, if I wanted one switch to switch phantom on for both preamps, am I okay to use one RC circuit for both or should I duplicate the RC circuit after the switch?

Thanks!

Yes it will shunt to ground which is fine and also discharges the 48v safely from the cap. Separate rc for each is ideal as it gives best separation between channels if there is any mismatch in the 6k8 resistors but for 2 channels you could share