This here is an A-B comparison sample between a modified and unmodified preamp channel on the M-Audio MobilePre audio interface I own.
It was recorded with an old AT-3031 small diaphragm condenser cardioid microphone, cabled with a 10m length of Canare L-4E6s Star-Quad cable.
The session was recorded in Pro Tools at a sampling rate of 48KHz with a bit depth of 24-bits.

The modification involved upgrading all the signal capacitors along the preamplifier's analog section.

Felix Alexander Wong