Hello to all.
Paraxod4, I agree with you, JCCON for the eyes of this Chinese clone. All sorts of Mundorfs are for McIntosh and Audionots.
An oscilloscope is a useful tool, it was not for nothing that it took for nothing. I looked at the form of power supply of the preliminary cascade, and there ripples, you can see it below in the photo.
Measured on diodes (katode):
In kit 5mV.
I decided to go extensively and increase the total capacitance of the test board. Now the total capacity is 80 000μF. I also laid a conductor with a cross-section of 4mm2 on the board from the OUT connector to the IN GND input, Now only my children can hear the fading quiet buzz. In principle, I am satisfied. It remains to test the power amplifier board and match it in volume with the preamplifier. I already wrote that the sound in acoustics sounds excessively loud at the beginning of volume control. Can someone suggest how to make it quieter by changing only the power amplifier circuit?