ETR-MONO can regulate a gain.
And ETR-MONO can regulate impedance.
Therefore, ETR-MONO realizes ideal frequency balance.
The numerical value of the left switch is the number of the winding of the coil of the InputCoil.
The numerical value of a central switch is the number of the winding of the coil of the OutputCoil.
An amplification rate is the ratio of the number of the winding.
The right switch can change the input impedance of the pre-amp.
Mint condition with box.