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I use to employ the two-point earth method to reduce AC filament hum. With this method there is no need for DC heating of the output tube filament. However, nowadays I employ a three-point method. One point is for signal, another for the low voltage power supply and the third is for the high voltage supply. Consulting the schematic, the earth symbol marked letter "S" is in regard to signal earth . "P1" and "P2" denote the earth points of the power supplies. |
Phono preamplifier section
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