I have an active crossover for bi-amping and have now built an input selector/volume control using ESP32, relays, opamp buffer and PGA2310.
Originally I was going to feed it from the filters grid transformer. It employs a dual half-wave rectifier to double supply voltages and SMPS modules down to +12V and +5V (in series). -12V linear. This, though, resulted in grid hum.
With a separate AC wallwart, it is silent.
Now once again I tried to feed it from the crossovers transformer and connected a line isolator/transformer on the lineout, but it still hums! How is this possible? The signal comes out clear otherwise. I can not see how there would be a ground loop anymore.
On another forum I got the suggestion to put 10nF commutation capacitors over the rectifier diodes, could this help?
Originally I was going to feed it from the filters grid transformer. It employs a dual half-wave rectifier to double supply voltages and SMPS modules down to +12V and +5V (in series). -12V linear. This, though, resulted in grid hum.
With a separate AC wallwart, it is silent.
Now once again I tried to feed it from the crossovers transformer and connected a line isolator/transformer on the lineout, but it still hums! How is this possible? The signal comes out clear otherwise. I can not see how there would be a ground loop anymore.
On another forum I got the suggestion to put 10nF commutation capacitors over the rectifier diodes, could this help?
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I cant draw at the moment but it is quite basic - has two half wave rectifiers; 1N4001 and respectable size electrolytic plus 100nF ceramic.
Negative side uses 7912 regulator and that feeds opamp and PGA2310.
Positive side uses one chinese SMPS/buck converter to 12V (opamp and PGA2310) and from 12V another buck converter down to 5V for digital logic.
Electrolytics and ceramics on all rails after regulators. 100nF on all chips' supply pins.
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