This page takes much of the stress out of designing a passive or active RIAA equalization network for a phono preamp. The sound transcribed onto a phono record's curves follows a special equalization curve so as to allow greater playback times (bass signals must be attenuated to conserve groove width) and lower high-frequency signal to noise ratios (high frequency signals must be accentuated to overwhelm the ticks and pops of a record's surface). At playback the reverse of the recording EQ curve must be employed to return the signal to a flat frequency curve. This equalization can be done actively or passively; Audio Gadgets does both calculations.

Active Equalization
The advantage of the feedback approach is consistency. Each channel will track the other to a very great degree in spite of aging parts or circuit wiring dissimilarities, as the feedback tends to iron everything out. The disadvantage is that because it is active, it can suffer from voltage overload and instability. Additionally, the varying amount of frequency dependent feedback can result in looser bass reproduction because of smaller amount of feedback at low frequencies and possibly a pinched, compressed high frequency playback due to excessive feedback ratios.

Passive Equalization
Passive RIAA equalization means brute force equalization: the frequency response is tailored to fit that of the RIAA curve by varying the amount of attenuation at different frequencies through a complex RC network. The advantages: no voltage overload, no feed-back, no instability problems. The disadvantages: no gain, insertion loss, impedance matching problems.

Resistor R3 often appears after a coupling cap so as to ground reference the gate or grid of the following stage. Its inclusion in the network will change the needed value for R1. If, on the other hand, it occurs prior to R1, then uncheck the "Include R3" check box.