Like the XP preamplifiers, the HPA-1 is the result of great attention to detail. 
Starting at the power cord, the AC line is first filtered for high-frequency noise and then isolated by a special toroidal transformer shielded by mu-metal for lower magnetic noise and shielded for electrostatic noise by a separate Faraday shield, grounded to analogue ground.

This is followed by fast/soft recovery rectifiers, generous CRC passive filtering and sophisticated discrete DC regulators and then more passive RC filters.
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