Cascading these two functions results in the same curve as the traditional two function combination creates. So, why bother with this alternate approach? Beyond the mental stretching, which is always for the good, this alternative approach engenders new phono preamp topologies, with some interesting benefits and one negative.  The first benefit is that the 50Hz low-pass filter can filter more power supply noise away from the output signal than the 2122Hz can.

frequency response. But if the bypass capacitor's value is reduced greatly, it introduces a shelving function, wherein the high-frequency gain is greater than the low-frequency gain, with the ratio being equal to the bypassed gain over the unbypassed gain or
                                    1            .
        Ratio =    1 + (mu + 1)Rk
                                  Ra + rp 
      The transition frequencies are based on the capacitor's value and the time constants it forms with the triode's rp and its plate and cathode resistor values:
       RkCk =  75µS
       [(Ra + rp)/(mu + 1) || Rk]Ck = 318µS
Of course, one triode is not going to provide enough gain in most cases, so additional gain stages will be needed.
      The overarching liability of this different path to RIAA equalization is the -12dB insertion loss beyond the expected losses, which brings it 1kHz insertion loss down to -32dB. With this equalization network, the near DC and subsonic frequencies are reduced by -12dB, whereas the traditional path retained all of the gain at the bottom of range. Now, -12dB is just too much to pay in most two-gain-stage phono preamps, but it is almost nothing in a three-gain-stage preamp, where the problem is usually having too much gain. Still the advantage of using a portion of the equalization network in double duty either, as a pseudo coupling capacitor or a partial cathode-bypass capacitor, is tempting.

           A single-triode phono preamp

   Second, the 500Hz to 2122Hz shelving network can be implemented within one grounded-cathode amplifier, i.e. a single triode RIAA equalized preamp. Usually a cathode resistor is bypassed with a large valued capacitor, so as to ensure adequate low-

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