This is the D3a that we have experimented with excellent result. Very natural sounding, finite details.
The Zobel network is used for damping of the ringing of the Hashimoto 10K;600 transformer.
It is possible to show with a minimum of test set if the trafo ha really a peak inside audio band.
In Riaa the upper limit considered is 20 kHz; if you terminate the secondary with 600 ohm only then you send a wide range of signal until 20 kHz you can read the output voltage on 600 ohm.
If it is costant is not need to put a Zobel.
Then it is possible to read the signal at the out of the complete stage following the Riaa table
It show at 1 kHz a loss of 20 dB and at 20 kHz another 20 dB
The Lcr has a costant impedance of 600 ohm and the 2k is in parallel with it at 20 KHz; at 10 Khz is little more than 2 kohm, 2.072
In Riaa the upper limit considered is 20 kHz; if you terminate the secondary with 600 ohm only then you send a wide range of signal until 20 kHz you can read the output voltage on 600 ohm.
If it is costant is not need to put a Zobel.
Then it is possible to read the signal at the out of the complete stage following the Riaa table
It show at 1 kHz a loss of 20 dB and at 20 kHz another 20 dB
The Lcr has a costant impedance of 600 ohm and the 2k is in parallel with it at 20 KHz; at 10 Khz is little more than 2 kohm, 2.072