In the video below, we present a real comparison of different audio sources with frequency spectrum analysis:

Each source was measured with the same equipment under identical conditions. You can hear the differences on your audio system and see them on spectrum charts. This is not theory - these are real measurements showing why preamp quality matters

For the tests, we used original recordings and vinyl records from the 70s. The input signal of each source was appropriately adjusted to achieve comparable RMS signal levels at the output.