~ RIAA–3 Configuration Calculator ~

This calculator like others I have made is to support the articles and comments on this website ~ It calculates the component values to make the classic passive 2 terminal 'lumped' or 'all in one' RIAA [or other] equalisation [EQ] network that I refer to as type RIAA–3 in this pdf and below ~ See this link for more about RIAA replay

A lumped EQ combines several filter time constants [TC] in a single network that requires less components due to the interaction between them providing the additional time constants ~ RIAA EQ is defined by 3 TC frequencies at which the a response changes ~ It has 2 Poles T1 T3 where response falls 6dB/octave and a Zero T2 at mid frequency where it rises

The T2 zero around 1kHz provides a region of flat amplitude and phase allowing a reference point to be easily established and it reduces the gain change between 20Hz and 20kHz to only 40dB rather than 60dB if only T3 were used ~ Zeros are not easy to make in practice and often a Zero and Pole [or two] are combined

This topology is by far the simplest to 'design' as R5×C5=T3 and R6×C6=T1 which are the 2 Poles ~ The ratio C5/C6 sets the Zero T2 and is exactly 3.6 ~ For my default RIAA values 27nF/7.5nF=3.6 and only R5 needs adjustment for correct EQ ~ You could have 36nF/10nF = 3.6 and R6=7.5kΩ with R5 adjusted 88.333kΩ ~ plus many others

T3  µs	T2  µs	T1  µs	Sig. Figures
ƒ=  Hz	ƒ=  Hz	ƒ=  Hz	Calculated –3dB corner frequencies for each T
The table below allows one component in each row to be changed and accurately calculates the other 3 ~ Check the columns R6 C5 and C6 for my default values have 3 identical values indicating these are correct and only R5 needs changing
R5  kΩ	R6  kΩ	C5  nF	C6  nF
R5  kΩ	R6   kΩ	C5  nF	C6  nF
R5  kΩ	R6  kΩ	C5  nF	C6  nF
R5  kΩ	R6  kΩ	C5  nF	C6  nF

The 2 terminal or current driven networks are often used in Negative Feedback loops and have been for many years especially in this topology ~ When driven from a low output impedance and terminated into a low resistive load RL the current through the network has an inverse RIAA characteristic

The rising current with with frequency develops a voltage across RL which could be a cathode [or emitter] load or part of an op-amp feedback loop and reduces the gain of the amplifier in accordance with the RIAA or BS1928 ~ Depending on the quality of the amplifier and the feedback topology used you may get acceptable results

I refer to 2 terminal networks as current driven because that is how I often use them ~ Not in a feedback loop around a voltage amplifier but as the output load on a Transconductance Amplifier which may be the collector of a transistor with un–bypassed emitter resistor or the anode circuit of a Cascode or Pentode where the current develops the equalised output voltage across the network ΐ

" Before the fall when they wrote it on the wall  ~ When there wasn't even any Hollywood "