I think that on our Soundcraft EFX12 the microphone pre-amps for two channels are blown. This because sounds are distorted and the peak light blinks even though a solo (pfl) indicates only -20 db levels.
I think this happened because people having been plugging in a piano in that channel, directly with a rca to xlr cable and no DI / impedance transformers.
Is it correct that using a line level (low impedance) signal on the microphone preamp (low impedance input) can 'blow' the pre-amp? If yes, would using the the jack input of the channel help to prevent this in future, or is that also a low impedance input?