Rather than a straight connection between U2a (the op-amp) and the U1 (the ADC), a simple anti-aliasing filter of 100R and 100nF can be fitted. Despite the simplicity of the filter, the effect on sound quality is surprisingly big.
The 100R is connected serially between U2a pin 1 and U1 pin 1. The 100nF is connected between U1 pin 1 and ground.
When working on an v1.0 PCB you will need to cut the trace between U2a pin 1 and U1 pin 1:
This can be done with an incision close to the U1 pin 1. Orienting the PCB viewing the solder side, and with the DB25 connector at the bottom, make your cut just above and to the left of U1 pin 1.
Rather than a straight connection between U2a (the op-amp) and the U1 (the ADC), a simple anti-aliasing filter of 100R and 100nF can be fitted. Despite the simplicity of the filter, the effect on sound quality is surprisingly big.
The 100R is connected serially between U2a pin 1 and U1 pin 1. The 100nF is connected between U1 pin 1 and ground.
When working on an v1.0 PCB you will need to cut the trace between U2a pin 1 and U1 pin 1: This can be done with an incision close to the U1 pin 1. Orienting the PCB viewing the solder side, and with the DB25 connector at the bottom, make your cut just above and to the left of U1 pin 1.
BOM 1 of 100ohm resistor 1 of 100nF capacitor