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 analog ground. This is followed by fast/soft recovery rectifiers, generous CRC passive filtering and sophisticated discrete DC regulators and then more passive RC filters. The input switching system uses relays good enough to switch moving coil levels. Logic is employed to control transition muting and restoration of default settings, and the exclusive use of headphone output and high level preamp output. The volume control is the highest quality Alps dual potentiometer, the connectors are Neutrik and Cardas. The circuitry is a simple Class A two-stage CFA topology using cascoded ultra-low noise Toshiba Jfets driving complementary Fairchild power Mosfets. The measured performance is superb, and the sound even more so.

Specifications
- Gain (dB): 8 dB
- Power Consumption (W): 23 Watts
- Output Power into 20 ohms: 3500 mW
- Output Power into 300 ohms: 200 mW
- Frequency Response 10hz -100k: -1 dB
- THD + Noise: < 0.005 at 1V out
- Input Impedance: 50K Ohm
- Output Impedance: < 2 ohms
- Weight: 6,3 kg
- 27,9 cm x 11,4 cm x 33 cm