I am building the pas-3 high level preamp. I outboarded the power supply using two power supplys. The B+ as well as an indepentant 12v filament supply that is not a voltage doubler. my question is do the returns of the two supplies need to be grounded together. I an experiencing 120hz hum.
Yes they need to have the commons joined together.
Sometimes the heater voltage is floated of 40 volts to decrease hum.
Sometimes the heater voltage is floated of 40 volts to decrease hum.
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