The Pleiades V6 headamp should have a push button called Fletsher-Munson, voice effort

The prototype of the Pleiades V6 should have a push button or toggle switch called FMVE.


A Pleiades (R,L) filter would be connected to any of the primaries of the input transformer.


Further reading:


Pleiades (R,L) filters - euroelectron


Flat frequency response from producer's brain to listener's brain, Sound Picture Recording and Reproducing Characteristics - D. P. Lowe, K. F. Morgan - J.S.M.P.E.