Practical Devices Corporation      

XM4 Specifications

DescriptionPortable Audio Headphone Amplifier
Weight140 grams (4.9oz) including alkaline battery
Power SourceLithium-Ion Rechargeable System, or,
9-volt Alkaline, or,
9.6V Lithium non-rechargeable, and/or
External power supply
External Power SupplyOptional Lithium-Ion adapter/charger, 120-240VAC, 50/60Hz worlwide compatible
Battery Charge Time (approx.)Lithium FastCharge system: 1.5 hours
Trickle charger NiMH: 15 hours
Battery Life (approx, depending on installed optionsAlkaline: 50 hours
Lithium-Ion: 40 hours
Lithium NON-rechargeable: 100 hours
Maximum Gain+12.7dB (Gain Boost disabled)
+23.1dB (Gain Boost enabled)
Frequency Response (20-20,000Hz, typical, front panel input+0.1dB, -0.4dB
-3dB Point (typical, front panel input)21 kHz at top end
9 Hz at low end
Total Harmonic Distortion THD (typical, front panel input)0.002%
Intermodulation Distortion (typical, front panel input)0.007%
Signal to Noise ratio (20-20,000Hz, typical, front panel input)100dB
Dynamic Range (20-20,000Hz, typical, front panel input)100dB
Bass Boost (approx.)+6dB @ 100Hz
CrossfeedUser-adjustable from mono to near-stereo using potentiometer;
User can bypass using pushbutton
Auto Power-OFFUser selects between 1, 3, or 6 hour poweroff interval, or unit can be set to stay on indefinitely.
Status IndicatorsTwo LEDs (one blue, one amber), indicating: low battery warning, battery voltage, and power
Integrated Voltmeter accuracy (typical)±100mV
  • Anodized aluminum case
  • Glossy anodized & etched face plate
  • Polished aluminum volume knob
  • FR-4 dual-layer impedance-controlled Printed Circuit Board with 1 oz. copper
  • Turn on both LEDs to full brightness;
  • Dimming mode: Allows user to optionally dim the blue LED;

Click here for the full audio test report.

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