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~ RIAA–3 Configuration Calculator ~

MICHAELAURALICE

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] replay equalisation [EQ] network that I refer to as type RIAA-3 in this pdf and the schematic below ~ See this link for more about RIAA replay

A lumped EQ combines several filter time constants 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 frequencies at which the amplified response changes ~ It has 2 poles T1 & T3 where gain falls with frequency at 6dB/octave and a zero T2 at mid frequency where gain increases until T1 negates it back to level

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 are combined but here all 3 time constants are established in a single block or lump

The 2 terminal lumped network can be used to provide record or playback EQ depending how it is driven or used within a negative feedback loop ~ This classic format network has been used since the beginning of electronic gramophone disc reply using valves and  is common today in negative feedback around op-amps but it is limited by output impedance and amplifier gain

This topology is by far the simplest to 'design' as R5•C5 = T3 = 3180µs and R6•C6 = T1 = 75µs which are the 2 poles ~ The ratio C5/C6 sets T2 and is exactly 3.6 and for my default standard values 27nF/7.5nF = 3.6 and only R5 needs ajustment for correct EQ ~ You also have 36nF/10nF = 3.6 so R6 = 10kΩ again with only R5 adjusted ~ plus many others

T3  µs T2  µs T1  µs Pre-populated for RIAA but can be changed
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
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

Nota Bene The 2 terminal or current driven networks are often used in negative feedback loops and have been for many years long before transistors and op-amps ~ 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 playback response

I refer to these 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 of a Transconductance amplifier which may be the collector of a transistor with un-bypassed emitter resistor or the anode circuit of Cascode or Pentode where the current develops the equalised output voltage across the network As shown here ΐ

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