Rare piece of 1980's Japanese obscura, Tokai Z-II Exciter TXC-2 . Seems to be a cross between a Pearl Thriller BOSS SP-1 as far as sound & funcution go, IMO . YMMV

from effectsdatabase;

Balance This knob regulates the direct sound and effect sound. Turning it to the right increases the effect sound, while turning it to the left increases the direct sound.
The TXC-2 produces a clear original sound effect with an overtone; additionally, it can be made clearer effect sound by the bright control. The players can enjoy the sound of the humbucking pickup with the overtone and can compensate distorting the high tone which happens when some effects were connected.

    Frequency This knob regulates the frequency of the peak of an overtone. As it is turned to the right the high tone is emphasized.
    Bright This knob is to add more range to the sound of the frequency. As it is turned to the right this effect becomes stronger.

What is exciter?

It is not quite right if you think the TXC Exciter simply changes a tone quality or makes a sound bright. It is the effect device that produces a clear and steady sound by adding harmonics to the original sound.

For example, the TXC has made it possible to get clear the faded sound which often happens with the sound of the humbucking pickup without changing the tone and also made it possible to get relieved the single-coil sound which has a tendency to get faint.

Furthermore, the TXC surely functions as a pre-amplifier for electric-acoustic  guitar, bass, etc., and as a buffer amplifier. Lets try