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of a Lifetime
Lil' Kaboosa says, Let's play it!


   The passive RIAA Phono Equalizer is an appealing circuit from an audiophile perspective for 2 main reasons.
 - The high frequency reproduction of the curve is extremely accurate
 - The two amplifiers operate with a constant feedback gain. High Frequency overload is lower than an active feedback design but this seems never to create problems in real world applications.

Here's a link to a schematic of the discrete gain stage I used in the first 5 years production of the EQS MK12 archival preamp. It is a scaled down version of the J. L. Hood Class A power amplifier. I added several boot strap circuits and a cascode input stage to improve peak to peak voltage swing. KG-1 Preamp.
RIAA EQ Network

FREQ. T uS R2 C1 C2
Hz uS OHMS uF uF
Hz uS

Choose A Value for R1 And Compute.
Adjust That Value Until The Values For C1 And C2 Come As Close To Standard Values As Possible.

Hz uS


  The math used to generate the values above comes courtesy of the Audio Engineering Society June 1979 issue - Vol. 27 #6.
  S. Lipshitz is the author of the fine article covering nearly every type of equalizer circuit including pre-emphasis, de-emphasis, passive and active circuits.
  Though the math seems complicated, a little study and patience reveals that it is really just a ratio of time constants. I have used the spreadsheet in all my designs and the accuracy is spot on. The only concerns are to be sure that the driving amplifier A1 has a low enough output impedance relative to R1 and that the following amplifier A2 has an input impedance of at least 50 times R1 to prevent loading.

  You can enter data for R1 and for the 3 frequency settings. Those frequencies represent corner frequencies of the 3 stages of the curve, the low end, the mid and the treble. If you have a different curve you would like to equalize, simply input the frequencies of interest and the spreadsheet will give you the component values.

If you feel this spreadsheet has enriched your hobby and want to donate something to us for having created it,
you can do that right here :
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