## Split passive RIAA Network for Tube Phono Amplifier

 The split RIAA method involves having two separate RC (passive) filters, each is driven by its own active stage. The network which is usually place first is that of R1, R2 and C1. The time constants for first stage are 3180µS (50,05Hz) for (R1 + R2) * C1 and 318µS (500,5Hz) for R2 * C1. Typical standard values used in tube circuits are: C1=33nF, C2=1nF The second stage defines a low-pass filter with a -3dB point of 75µS (2122Hz) and its time constant is 75µS (R3 * C2).

## Calculate R1, R2 and R3

 Capacitor values for Network C1 = nF C2 = nF Tube data (optional) Data Tube 1 Rp_1 = Ω (resistor between plate and power supply) Ri_1 (internal tube plate resistance ) = Ω (from tube datasheet) Ri + Rp = Ω R1 = Ω (incl. Ra and Ri)   Ω (theoretically) R2 = Ω R3 = Ω (incl. Ra and Ri)   Ω (theoretically)

 R1 = Ω parallel Ω = Ω, Error = % R2 = Ω parallel Ω = Ω, Error = % R3 = Ω parallel Ω = Ω, Error = %

 Please keep in mind that the output impedance of the first stage V1 throws the network time constants off. For example, a 12AX7 used in a grounded-cathode configuration with a 150k plate-load resistor results in an output impedance of roughly 44k (62k in parallel with 150k). When this value is added to equalization network R1, the error becomes more noticeable and moves in the opposite direction, giving a positive boost at 10Hz (+2.74dB). without changing C1 value and without changing C2, the output returns to close to flat, but with a slight bump (+0.05dB) in low bass. In the case of the op-amps, the output impedance is usually well under 100 ohms, nothing has to change...

## RIAA Playback Curve Attenuation in dB relative to 1kHz

 > Frequency > Attenuation in dB > Frequency > Attenuation in dB 10 19.74 1000 0 20 19.27 1200 -0.61 30 18.59 1500 -1.4 40 17.79 1800 -2.12 50 16.95 2000 -2.59 60 16.1 3000 -4.74 80 14.51 4000 -6.61 100 13.09 5000 -8.21 120 11.85 6000 -9.6 150 10.27 8000 -11.89 180 8.97 10000 -13.73 200 8.22 12000 -15.26 300 5.48 15000 -17.16 400 3.78 18000 -18.72 500 2.65 20000 -19.62 600 1.84 30000 -23.12 800 0.75 40000 -25.6

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