Kemper Stage Head phone signal is "more saturated with effects" than the main signal - what to do?

What is the setting of the Headphone Out?

Have you investigated the Space parameter that's applied to the headphone out?

Quote from Main Manual, Output Secion - Space

The “Space” parameter adds a small room simulation to the master signal. This makes listening through headphones far more enjoyable.

A brief explanation: whenever you listen to a sound coming from loudspeakers, you are also hearing the reflections from the floor, the walls and objects around you. Even when you listen to a mono signal, these additional reflections will still result in a stereo image once they reach your ears. There is only one common situation where no natural reflections happen, and that is when you listen through headphones; as your ears are, biologically speaking, not suited to this, it can quickly lead to listener fatigue. This effect is called “in-the-head localization” and becomes particularly noticeable when you listen to a mono signal.

By using the Space effect, you can add virtual reflections, to create a sense of room and natural space. A mono signal will be converted to a subtle stereo image, which should be far more pleasing to your ears. Even though this effect is designed for headphones, you may also find it appropriate for listening through regular speakers, or for recording. By selecting the option “Space>HeadphOnly”, you can select whether it is applied to the HEADPHONE output only, or to the MAIN OUTPUT as well.

You can also apply the Space effect to individual Rigs, rather than activating it globally in the Output Section. In this case, simply use the TYPE knob to select it in either the X or MOD effect.

The Space effect is also very useful for improving the sound of in-ear monitors on stage. Unfortunately, in most situations, both stage-monitoring and FOH are derived from the MAIN OUTPUT - as a result, the effect will appear on the main PA as well. As long as you use Space at a suitably low Intensity setting, it will not be noticeable on the PA sound, but will still create a reasonable effect on your in-ear monitors. Needless to say, the monitor signal must be supplied in stereo for Space to have the desired effect.

the headphone output will always deliver the Master Stereo output source.

As Ruefus already stated the difference could be caused by the Space effect that is activated for the headphones by default. You can either activate it for all outputs or turn it down for the headphone output if you find that it is adding too much ambiance.

If you still encounter the issue please try a different pair of headphones or if you use an adapter try a different one. Maybe the one you are currently using is causing some phase issues which can potentially cause a misbalance between the dry and wet signal ratio.

there are no settings for the headphones other than level and Space amount. These are available in all Profiler models.

then try a different pair of headphones or a different adapter

Quote from ThomasMH

I have tried to toggle on/off. The problem remains.

there is no toggle on/off option for the Space effect. Maybe you are confusing that with the Space/Headphones only option? That controls if the space effect is also present at the other outputs. To turn the space effect off you need to turn the value dial all the way to the left for the space parameter.

I know what this is :). The stage headphone output plug is slightly of spec, so with some plugs it short circuits and you only get the "side" signal. Try pulling out the headphone plug slightly. Like 1 mm. or less.