Inductive RIAA deemphasis Networks

noticeable worldwide interest in the using of Inductive RIAA networks has always been driven by the desire to obtain the best possible sound quality.

The RIAA emphasis (at the recording) , a process necessary to reduce the amplitude of lower frequency and amplify the higher ones for mechanical reasons (primary to efficiently write audio information on vinyl surface ), was historically obtained by a passive LCR network. Clearly the corresponding RIAA deemphasis can be obtained at the best (i.e. with the maximum accuracy) only by a similar dual network

In a theoretical way, any transfer function can be synthesized by an LCR network (passive solution) or by an active RC network (where this network is placed in the feedback loop of an operational, or similar, amplifier).

Audiophile community seems to refuse the active solution since the RC network is placed around a feedback loop ( no matter if the active device is a vacuum tube or a solid state amplifier) and for good reasons, since there is an historical, anecdotal and technical evidence that feedback amplifiers alter sound quality: for this reason the only acceptable way to build a good phono preamp is by the use of a passive stage (split or not around gain stages ).

For economic reasons passive RIAA deemphasis networks are rarely in the form of a LCR quadripole (see schematic of the Tango EQ-600P) which is the only way to obtain the maximum accuracy, but appear (like 99% of all phono stages) in the lighter and less accurate form of a RC network.

Japanese Phono with Inductive RIAA, (from Radio Gijutsu, M. Yoshio Nasu, 1984)