This way, you will never hear the dry mic signal (because it's hard panned right), but you can still mix other signals into the mono channel, and you can use the EFX send to selectively put signals through to the compressor. Then only use the left main out from the mixer. Run EFX send to the compressor, and EFX return to L in mono.
To elaborate, send the mic to channel 1 and hard pan this channel to R, also sending to EFX. Treat the mixer as mono, and use one of the two channels with the effects send/return to run the compressor.Maybe you can hard pan your vocal mic to L, put your other sources hard panned to R, and then run the compressor only after the L out from the mixer. Depending on what else you're mixing, this might or might not be useful. Neither of those will work without some energy to power up. Not only condenser microphones, in fact every active DI Box needs phantom power to work as well. The main purpose of this phantom energy is to power active circuits, so they can work properly. Just throw the compressor after the main outs of your mixer. Know how your interface supplies the power for each channel Using the Phantom Power.If the mic says it needs phantom power, it needs phantom power. Phantom power is needed for certain mics. Thanks to onboard phantom power, Q502USBs Xenyx microphone preamp can handle dynamic, as well as a studio-grade condenser microphone. You should consider an audio interface that provides phantom power, at least in the future. Two options I can think of that you might be able to use as a workaround: The Behringer Xenyx Q502USB USB Audio Mixer is simply excellent, the 5-input, 2-bus mixer with everything you need for incredible sound. As you've noted, you don't have inserts, but you do have an additive effects loop.
So, you've got to figure out how to integrate the compressor into the signal chain after the preamp. Nothing should come between your mic and mic preamp except very specific applications - something like a kill switch or a phase inverter or something. Even if you injected phantom power between the compressor and the mic, then you're still trying to make the compressor work with mic-level signal. The compressor wants to use line-level signal as input and output. Your mixer contains a very important component, which is the mic preamp. 2 Microphone inputs with 48 V phantom power, 3-band EQ, compressor and peak. The short answer is no, and don't do that. 0 and I know you have to buy an XLR adapter so it can work on this mixer.