See also Pleiades V6 2DV4 Nuvistor electron tube booster amp.
Or Pleiades V1 electrometer tube booster amp.
Both front end amplifiers operate with only 1.3V as plate or anode supply.
Not only bass exaggeration is removed but also high frequency exaggeration. Both in a gentle way and possibly slope. This seems to be a desirable byproduct of very low anode current, of the order of a few microamperes. Hiss goes down too but of course these amplifiers could have better noise figures. They do not seem to be as magically quiet as when such tubes including the EF183 are operated at 25-50μA at plate supply for example of 3.9V. See previous posts.
Treble is natural too. (The more a singer is singing softly, the more bass and high frequencies are produced compared to mid band, (voice effort frequency spectrum curves)). The above booster amplifiers compensate for this. And also for louder reproduction than the original acoustic intensity where our brain exaggerates bass and treble frequencies [Loye, Morgan].
Reference:
(Flat frequency response form producer's brain to listeners brain), Sound Picture Recording and Reproducing Characteristics - D. P. Loye, K. F. Morgan - Journal of the Society of Motion Picture Engineers
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