I try to use my Rode SmartLav+ with Scarlett 2i2 USB pre-amp. I already bought Rode SC3 adaptor and small jack to big jack adaptor. I try to use any of the line/instrument inputs on my pre-amp, but it doesn't work. Of course when I plug Rode SmartLav+ to my smartphone or laptop it works. From the other hand, when I plug my Beyerdynamic set with Scarlett pre-amp it also works. I've also checked small jack to big jack adaptor and it works with eg. headset. How do you think - what can be a problem?
Below I provide images for my configuration. When mic is plugged-in to pre-amp the o'ring of the gain potentiometer is not even "turned-on" (it has diode indicator which cause it to shine green, yellow or red depending on the mic sound input).
Rode has now a device which allows to plug in microphones which need to be powered by power usually provided by smartphones (2.7v) through TRRS such as Rode's Lavalier Go or Shure's MVL/A to a USB sound card or any mic entry using XLR.
This is Rode VXLR+. The XLR has to provide 12-48V phantom power.
The VXLR+ is a 3.5mm female TRS socket to male XLR adaptor, which will convert 12-48V Phantom Power down to 3-5V 'Plug in Power', allowing RØDE on-camera microphones such as the VideoMicro and VideoMic GO, as well as self-worn microphones like the HS2 Headset Mic to receive power from the XLR input. The 3.5mm socket also features the same threaded connector as used on the output cable of the HS2 Headset Microphone, and the RØDELink Filmmaker Kit Receiver, ensuring the connection to your XLR input is secure and won't disconnect during your recording.
I've found an answer to my question. RODE SmartLav+ is a plug-in powered microphone, thus it needs around 5V powering. That's why it works with smartphones, laptops, and most cameras, and do not work with Scarlett 2i2 pre-amp which has only 48V phantom powering. The solution to my problem is an external power supply for the mic, which can be something like this. Anyway, thanks for the answers.