My phono pre gives these instruction and has these grounding switches as part of its circuit.
Improper grounding of an outboard phono sections can often result in excessive hum. Since the grounding on every sytem is different, it is impossible to provide a uniform grounding strategy that will work for every system. Be assured that with correct grounding almost all audible hum can be eliminated. If you are experiencing some hum, try the following:
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Be sure to have the phono pre plugged into the same outlet or power strip as your preamplifier.
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Connect the turntable ground to the ground lug on the rear of the Phon Pre
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You may need to connect a ground wire from the Phono pre to your preamplifier.
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Try different combinations of the internal grounding switches g1-g4 under the Phono Pre access panel
Grounding switches g1 through g4:
The four small grounding switches g1, g2, g3, g4 will most often be set in the forward position as shown in the preceding photographs. If you are experiencing excessive hum you can try moving them in the various possible configurations g1, g3 forward g2, g4 to the rear, etc.. Some cartridges that share internal grounding between channels may require that one channel be grounded while the other is not (e.g. g1, g2 forward and g3, g4 to the rear).
Some or all of the above should eliminate most hum. If this fails to cure the hum, call customer service for further advice.
If not GoChurchGo trying Thoughts & Prayers may work