KAB PASSIVE RIAA EQ NETWORK
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.
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.
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.