~ 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 2 terminal 2CR 'lumped' or 'all in one' equalisation [EQ] network that I refer to as type RIAA–3 in this pdf and below and this link with 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 ~ It has 2 Poles T1 T3 where the response falls 6dB/octave and a Zero T2 at mid frequency [≈1kHz] where it rises

The RIAA T2 zero around 1kHz provides a region of flat amplitude and phase allowing a reference point to be easily established and it reduces the overall 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 creates the Zero T2 ~ For the RIAA default values shown 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 to 88.33̇kΩ ~ 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 ~ The columns R6 C5 and C6 for the default values each 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

These 2 terminal 2CR 'current driven' networks are often used in Negative Feedback loops and have been for many years especially using this topology ~ When driven from a low output impedance and terminated into a low resistive load [Rfb] the current through the network and Rfb has an inverse RIAA Record characteristic

The rising current with with frequency develops a voltage across Rfb which could be a cathode or emitter resistor 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 the 2 terminal 2CR 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 of a 'Transconductance Amplifier' which may be a transistor or valve cascode or the anode circuit of a Pentode as shown here where the current becomes the equalised output voltage across the network

Unlike networks RIAA–1 and RIAA–2 this topology and RIAA– 4 cannot readily be corrected for response errors due to the impedances either side or across the network due to high values Rfb [NFB] and amplifier output impedance which upset the response and cannot be fully corrected by making R5 larger as some designs do ΐ

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