Tohle zní rozumně (odpověd na moji otázku na GS). Dip switche jsou na prd a neobratné na ovládání, čili rozumná varianta je připojovat mikrofony při odpojeném USBPre a pak ho zapojit. Odpojování už není problém
"It's not a simple "either - or" issue. It depends on the specific hardware involved.
The potential for damage is not to the mic but to the mic pre input circuitry. When a mic is plugged into an already powered input of a non-transformer coupled mic pre, the input coupling caps must charge rapidly. That high-current surge can produce an over-voltage condition at the input stage (after the coupling caps). Most mic pres use either power rail clamp diodes, zener diodes or sometimes both to limit the voltage spike caused by the current surge. The PP series resistors also limit the charging current.
For most mic pres, the protection is adequate, but there have been some notable "high-end" mic pres that omit the protection diodes (to slightly improve the absolute noise floor measurements) that can be damaged by simply plugging in a mic with PP on. At least one "high-end" mic pre manufacturer states that mics should be always connected before PP is turned on to protect their preamps.
There are also a few mixers with minimal mic protection circuits. Repeated application of over-voltage spikes to a poorly protected solid state mic input will usually not result in a complete failure (an input short) instead the surges can slowly degrade the performance of the input junctions in the [usual] integrated circuit op-amp. That can result in increased input stage noise, and decreased open loop gain resulting in slightly increased distortion. Those changes can be subtle and go unnoticed by most users.
I own and use a Sound Devices USBPre2 with a MacBook Pro. SD usually provides proper protection to their mic inputs, but I've not seen a schematic of the USBPre2. My solution is to always connect the mics, connect the USB cable to the MacBook, and only then power up the MacBook. It's probably not necessary with a USBPre2, but it's easy to do, so why take chances?
Most DIP switches are intended for light, occasional use, and as noted, the ones on the USBPre2 are not easy to get at or to operate. I just leave them on, but reduce the stress to the mic inputs by only connecting when the USBPre2 is powered down.
Disconnecting a mic simply breaks the circuit and doesn't create the potential for over-voltage surge damage that connecting does, so that's not an issue."