I made the following changes to the RIAA stage to improve its accuracy:
- Measured all caps
- Adjusted 75uS network to compensate for the capacitor variance and the cascode output impedance
- Adjusted 318uS and 3180uS networks to compensate for the capacitor variance
All resistors were adjusted with a pair of 0.1% SMD resistors to avoid series connection to reduce noise level.
As shown below, the response is really good matching at less than 1% for frequencies above 50Hz. the error at low frequency is due to the rumble low pass filter, the hum and the soundcard LF response which introduce a slight distortion at very low frequency in the MLS measurement:
| Frequency (Hz) | Test (dB) | RIAA (dB) | Error |
| 20 | 18.80 | 19.27 | 2.44% |
| 100 | 13.00 | 13.09 | 0.69% |
| 1,000 | 0.00 | 0.00 | 0.00% |
| 10,000 | -13.70 | -13.73 | 0.22% |
