06-23-2020, 11:58 AM
Solving noise problem on the other board with MKT capacitors. The main reason is the no clock synchronization of chips. Both TPA3116 works in master mode independently of each other. Another problem is the manufacturer chose a high gain of 36dB and left the input capacitors of the same value as for the 20dB gain. The difference is in the input impedance. for 36dB it is 9k and for 20dB 60k. The capacity of 1u5 condensers is good for 20dB, for 36dB it should be 10u. The gain is too big for a DAC. 20dB is enough. Then the soldered capacitors will be OK. We peel off the heat sinks. We choose one zTPA3116 as master. Next to it we find a 47k resistor, change it to a 5k6 resistor. We remove the 75k resistor. With the second TPA3116 which will be a slave 47k resistor replace with 51k, 75k resistor replace with 51k. It still allows you to make a synchronization link. we connect together through a 4k7 resistor legs 16 of both systems. They are from the page of the potentiometer and from the page of 3116 inscriptions on the PCB. Additionally, we solder a 27p - 47p capacitor between the leg 16 of the slave system and the mass - e.g. pins 14, 15. End of the modification, we stick with heat-transfer glue heat sinks. The potentiometer may be replaced for better quality.
Another issue is the choice of timing. Chinese module manufacturers choose a 400kHz clock (pins 13, 14, 15 shorted to ground). You can switch clock speed to 1200kHz. Pin 13 should be desoldered from the pad on the PCB and connected with pin 7 through a 100k resistor. At synchornic operation of two circuits with 1200khz clock on the slave side the capacitor connecting pin 16 with mass should probably have a reduced frequency to 4p7 - 10p. All resistors on the PCB are SMD size 0603.
Another issue is the choice of timing. Chinese module manufacturers choose a 400kHz clock (pins 13, 14, 15 shorted to ground). You can switch clock speed to 1200kHz. Pin 13 should be desoldered from the pad on the PCB and connected with pin 7 through a 100k resistor. At synchornic operation of two circuits with 1200khz clock on the slave side the capacitor connecting pin 16 with mass should probably have a reduced frequency to 4p7 - 10p. All resistors on the PCB are SMD size 0603.