The manuscript by Lin et al. presents a new home-built instrument for magnetotelluric measurements. The main feature of the new instrument is an increase of the sample rate to 2.5 MHz, which can potentially open for more shallow targets than current state-of-the-art instruments.  Generally, the manuscript is well written and easy to follow. The instrument-oriented manuscript fits nicely within the scope of the GI journal. I would have preferred it if the authors had provided more technical details, but I also understand why this manuscript is mainly written as an instrument paper at the system level. English language is fine and easy to understand. A few more “The” might need to be added by the Copernicus staff during editing.

Figure1: It appears that the Bx, By, Bz part of the figure is based on a left-handed coordinate system. Please check that this figure visually presents as intended.

Line 80: The analog board is connected to both electric and magnetic field sensors. Please elaborate on the sensors and the necessary electrical protection and signal conditioning of the instrument

Line142: It is not clear what the function of the signal calibration module is. Please add details on (the purpose of) the output reference signals.

Line 143: The sentence on the frequency range of the instrument is unclear. Please rephrase and avoid the three “to” right after one another.

Line 158: “using use”?

Line 163, table 1. I’m not familiar with the instruments presented in the table, but I find it a bit odd to see that the 16-bit Zonge-GDP-32II has a 190 dB dynamic range. This indicates that some further tricks are needed. Please clarify and discuss in paper.

Line 185, Figure 11/12. It would be appropriate to augment both figures with a frequency analysis of the recorded data to show the spectral purity of the sine waves (Figure 11) as well as the shape of the noise floor of the instrument (Figure 12).

Line 185. Please add more detail on the data and calculations from which the 143 dB dynamic range is determined. The theoretical maximum dynamic range of a 24-bit converter is 144 dB and I am a bit surprised to learn that this instrument is so close to the maximum.

Line 192, Figure 15/16.These figures can be merged into one figure, and they should be plotted with a logarithmic y-axis. This choice of axis formatting will make the noise floor visible, and the performance of the instrument can be much better assessed. It would also be appropriate to show actual data and discuss the quality of these.

See my comments in the pdf file.