Riaa topologies

     Not too long ago, all tube phono preamps had very similar circuits. Usually they held two cascading gain stages that were often followed by a unity-gain buffer (a cathode follower), which always ended in a feedback loop that actively realized the inverse RIAA equalization curve. This is the topology found in the Audible Illusion Mini-Mite, the Berning P-1, most Conrad Johnson's early preamps, Dynaco PAS-3, Lux 3300, Marantz 7 and C-22, all of the MFA preamps, the Precision Fidelity C-4, and numerous Audio Research preamps, SP-6, etc.

This basic topology offered a simple way to achieve feedback and equalization in one step. 

      Active RIAA eq means feedback eq. The varying amount of feedback depending on frequency can produce loose bass (less feedback at low freq) and pinched high freq response due to the excess feedback near 20kHz.
      In the late 70s, the great French audiophile and tube specialist Jean Hiraga designed a preamp with zero global feedback loops and with a passively equalized output signal.

      We agree that passive eq sounds much better than active eq and jfets act like solid state tubes.

      Active RIAA equalisation means that the related filter forms a part of the feedback circuit. The feedback type of RIAA correction filter by nature is prone to induce Transient Intermodulation Distortion (TIM) and changes the sound for (experienced) listeners. The active RIAA equalisation circuit is relative simple and is also cheap.

      The passive RIAA equalisation circuit is built in-line as a series chain of filter sections between the input circuit and the line amplifier. The total signal gain is the same, but the effect on the replay sound quality is less because there is no TIM anymore. Also the sound is evaluated as being “faster”.

      Phono amplifiers with passive RIAA circuits do cost somewhat more because there are more components involved. We use a composite RIAA network instead of a split RIAA. Its main advantage is that it only requires two active gain stages , this having the huge of advantage phase linearity - yes your phono stage will be absolute phase linear to join up nicely with your line stages.

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