How could this work? (+/-24v w/ 48v)

So, re-racking a pair of clrec modules that were seemingly well done but quite ugly. The external power supply is a bipolar 24vdc power one. Somehow the previous setup was getting phantom out of it as well. I would assume they were using the -24v as the phantom common.

How can this work though if pin 1 is tied to the chassis and  the +/-24v common? Would I have to float pin 1 from the chassis?

RSRecords said:

So, re-racking a pair of clrec modules that were seemingly well done but quite ugly. The external power supply is a bipolar 24vdc power one. Somehow the previous setup was getting phantom out of it as well. I would assume they were using the -24v as the phantom common.

How can this work though if pin 1 is tied to the chassis and  the +/-24v common? Would I have to float pin 1 from the chassis?

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Pin 1 MUST be connected to the chassis. Instead, you use a virtual ground. Like in guitar pedals. Preferably it should be active using an op amp to drive the ground (as opposed to a giant capacitor between the virtual ground and -24 which is earth ground. But you can't really source / sink a lot of current from / to the virtual ground. You can only use it to bias things. Or at least you should only use it to bias things. So if there are outputs of amps driving into ground or LEDs or relays dumping current into ground, it's not a good idea. And you need caps on outputs if they're not transformer outs. If you have a pointer to a schem I can tell you if it will work well or not.

The virtual ground trick works perfectly fine if you're just biasing an op amp input or sourcing and sinking equal currents through at least 10K or so. But otherwise, for a pro-build, I personally would just get two appropriately sized 24V SMPS and the smallest 48V SMPS you can find. Then stack the 24V so that the intersection of the two is your ground (which you can now connect the chassis and pin 1). Or maybe get another very small 24V and stack that on top of the upper 24V. Both 24 and 48 are common voltages for stock SMPS. I like the MeanWell supplies but they get some hate around here for being LED supplies. For some reason people don't realize that they're all LED supplies. I have no clue why it would many any difference. 200mV ripple at 50kHz is easy going with a small choke and an even smaller cap. That can make a really nice clean, sturdy supply with no mains hum.

Ok that makes sense. I guess I'm just not sure how it could've been wired before so as to have a 48v phantom rail. Seems impossible to me without a virtual ground like you said.
For  a solution, I was thinking to add a small 48v SmPS. I recently (in another thread)  had some success using a CLC filter. Any issues to be aware of if adding the switch mode common to the bipolar common? Potential for introducing noise?

It must be that it's already setup for virtual ground. If they connected pin 1 to -24 (and not to the chassis obviously), aside from the fact that it would not be correctly earth grounded and therefore unsafe, the mic body would be at -24 relative to earth ground. That's not much voltage but the current might not be limited so much. So if the mic touched something earth grounded, it would at least blow the fuse (hopefully) but might cause something to get hot or damage something.