The entire true balance differential circuit board inside the EX is brand new. Technically speaking, it is a completely new preamplifier. The following picture above is a spectrograph. There are 7 singular frequencies fed into the amplifier and they are represented by 7 sharp vertical spikes that each go up to about “-95” on the vertical scale on the left hand side.
Both K-15 and the K15EX show the 7 singular frequencies. Now looking lower down towards the bottom, you can see a whole bunch of shorter vertical lines, mostly in red. Each of those lines represents a new frequency the amplifier has generated (Distortion) and the height of each line indicates the strength of each distortion.
You will see that there is also a little bit in green (becoming yellow if it coincides with red). The green graph is for K15EX and the red graph is for the original K-15. This is NOT an illustration. It is a high powered simulation.
The results show K15EX does substantially better than the K15. On average, not only are the intensity of each distortion reduced by about 30 times but also K15EX has fewer of them to begin with.