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Copyright © 2015 Practical Devices Corporation. All rights reserved.
Practical Devices Corporation      
 

XM5 Portable Headphone Amplifier
Product Details
XM5 Headphone Amplifier

Practical Devices Corporation is pleased to announce their latest product: the XM5 Portable Headphone Amplifier. We've worked hard to provide you with what may be one of the most advanced, feature-packed, and best-sounding portable headphone amplifiers on the market today. The XM5 is designed to be durable, flexible, easy to use, and above all, offer incredible sound quality.

Unlike many other portable headphone amplifiers on the market, we've added every possible useful feature we could think of, such as Microprocessor control, Auto-PowerOFF, Variable Crossfeed, integrated battery charger, a DC power jack - the list goes on.

Before you buy another amplifier, compare it to the XM5's feature list:

  • USB DAC
  • Anodized extruded aluminum case
  • Laser-anodized glossy aluminum faceplate
  • Bass Boost of +6dB @ 100Hz when enabled
  • Treble Boost of +2.5dB @ 10kHz when enabled
  • Variable crossfeed, user-adjustable, with bypass
  • Auto Power-off, saves battery life
  • Maximum gain is switch-settable by user
  • Integrated voltmeter displays battery voltage
  • Low battery indicator
  • Blue LED and amber LED indicate status.
  • FlashLight mode
  • Microprocessor controlled
  • Gold-plated amp chip socket, allows for amp upgrades
  • Power jack allows external power supply to ower the unit and recharge the battery.
  • Ergonomic compact design for portability.
  • Uses TLE2426 rail splitter, with noise reduction, to create a stable and low-noise analog ground.
  • Uses dual OPA134 ultra-low distortion (.00008%) low-noise high performance audio amplifier.
  • Audio power supply bypassing uses both high-value Electrolytic and Tantalum and Ceramic capacitors to create an ultra-stable low-noise low-impedance power supply.
  • Polished Aluminum volume knob.
  • Proper dual-layer impedance-controlled Printed Circuit Board.
  • Optional Lithium-Ion FastCharge® System is available.

Block Diagram of XM5 Headphone Amplifier


Audio Performance and Quality 

The XM5 is constructed using only high-quality audio components:
Amplifier Stage:
  • Burr-Brown OPA134 ultra-low-distortion low-noise high-performance Audio Amplifier: The heart of the amplifier stage uses the well-respected Burr-Brown OPA134 ultra-low-distortion (.00008%) low-noise high-performance audio amplifier.
  • Mil-spec 0.1% metal film feedback resistors: The feedback stage around the amplifier uses Military-spec (MIL-R-10509) 0.1% metal film resistors, chosen for their very low noise and excellent high-frequency characteristics (Vishay-Dale RN55 series).

Audio Power Supply Stage:
  • Texas Instruments TLE2426 Precision Virtual Ground: Powering the audio stage is the split-rail power supply, which is created by the Texas Instruments TLE2426 "Rail Splitter" Precision Virtual Ground. To further reduce noise and improve ripple rejection, the TLE2426's noise reduction pin is used
  • Tantalum and high-value Electrolytic Capacitors: To further improve the stability of the power rails, a combination of both Tantalum and high-value Electrolytic capacitors are used. Electrolytic capacitors provide bulk decoupling of the power rails, but due to electrolytics' relatively-high ESR (Equivalent Series Resistance - a small unavoidable parasitic resistance in series with the capacitor), electrolytics do not have good high-frequency performance. Therefore, Tantalum capacitors, with their excellent ultra-low ESR performance, are used to fill in the spectrum where the electrolytics left off. The result is an exceptionally stable low-noise power supply for the audio stage.

PCB Layout:
  • Professional Printed Circuit Board. The XM5 uses a proper professionally-built FR-4 impedance-controlled PCB. Care was taken during the design of the PCB to ensure audio signals have ground shielding and a low-impedance return path, which is not possible with any hand-wired board.

The result of this attention to detail and the utilization of only high-quality parts is an amplifier of remarkable quality. As we said before, You cannot get a higher-quality and more feature-packed headphone amplifier than the XM5.

The PushButton 

Push once to turn unit ON, push and hold to turn it OFF.
  • Press ONCE to turn on the power for at least ONE hour.
  • Press THREE times -- " -- THREE hours (Blue led flashes 3 times in response)
  • Press SIX times -- " -- SIX hours (Blue led flashes 6 times in response).
  • Press SEVEN times -- " -- FOREVER (Blue led 7 flashes; unit must be turned off manually)


  • Press ONCE to display battery voltage (The Amber Led flashes the battery voltage. For example, if the voltage is 8.5volts, the Led will flash 8, then 5 times.
  • Press TWO times to toggle Flashlight mode
  • Press FIVE times to toggle the Blue Led brightness


  • PRESS and HOLD for 3 seconds to Power OFF.

When pressing for the above functions, you must do all the presses within a three second window.

The most-commonly used functions are, of course, ON and OFF, so we've made these the simplest button-pushes: Push ONCE for ON, and Push and HOLD for OFF.

Bass & Treble Boost

The XM5 is equipped with switchable Bass and Treble Boost:

Bass Boost button IN:+6dB @ 100Hz (approx.)
Bass Boost button OUT:+0dB @ 100Hz

Treble Boost button IN:+3dB @ 10kHz (approx.)
Treble Boost button OUT:+0dB @ 10kHz

Variable CrossFeed

The XM5 is equipped with Active Variable Crossfeed. To use Crossfeed, the Crossfeed Enable switch must be in the IN position. Then, you can adjust the amount of crossfeed using the Crossfeed Adjuster potentiometer.

Why You Want Crossfeed: Most music is mixed to be listened to on loudspeakers. The studio technicians mixing the recording assume there will be alot of crosstalk, since, with speakers, the listener's left ear clearly hears the right speaker's output, and vice versa. Thus, most music is mixed with a very wide stereo soundstage.

With headphones, however, the left ear only hears the left channel, and the right ear only hears the right channel, with nearly zero crosstalk. This can, for many recordings, cause the soundstage to appear to be "in the center of your head". Further, some recordings (early Beatles' recordings are infamous for this) have each instrument and vocal track panned 100% to either left or right, which can almost immediately cause listener fatigue.

The XM5's CrossFeed feature feeds some of the left channel into the right channel, and vice versa. In order to properly simulate the forward soundstage of loudspeakers, the amount of crossfeed needs to vary with frequency, which the XM5 does. Low frequencies (bass) bend around corners (including the corners of your head - bass from the left speaker will bend around your head and enter your right ear) much better than higher treble frequencies (treble is more directional); thus more crossfeed must occur in the lower bass frequencies.

Further, the XM5 allows the user to adjust the overall level of crossfeed, from near-stereo to complete mono. This is adjusted using the crossfeed controller potentiometer inside the unit (don't forget to turn on the crossfeed with the CrossFeed Bypass Switch).

The crossfeed vs frequency plot, shown for various crossfeed potentiometer positions, is shown below:
XM5 Active Variable Crosstalk
Don't confuse this graph with a Frequency Response (also known as Amplitude Response) graph; This Crossfeed graph shows how much one channel is fed into the other, whereas the Frequency Response of the XM5 is always near-perfectly flat (except when the Bass or Treble Boost is enabled, of course). The Frequency Response graph is shown in the "Specifications" section.

Gain

With the Main Volume knob at full volume, the overall gain for the XM5 is:

Gain with gain boost enabled:

+20.6dB

Gain with gain boost disabled:

+12.1dB

It is preferable to not use the gain boost (ie. It is preferable to remove the jumpers) unless you need it. "Need it" means your headphones are too quiet, even with the volume knob turned up to maximum. This is because too high a gain will result in a tendency to turn the volume down on your audio source (mp3 player, etc), and weak sources are more susceptible to noise.

Usually, only very high-impedance headphones (300Ω or above) require the gain boost.

Ergonomics

The XM5 was designed with ergonomics and portability in mind. The main volume, status LEDs, power button, and both input and output jacks are all located at one end of the unit, allowing the XM5 to be easily carried in a pocket.

The extruded aluminum case and internals are machined to give a snug fit, with no rattles or loose batteries, or risks of short circuits.

The unit has a "FlashLight" mode, which turns on both LEDs to full brightness. Not too useful for, say, spelunking, but the focussed LEDs are quite strong and very handy if you're fumbling for your keys in the dark, for example.

Finally, the XM5 weighs only 157 grams (5.5 oz), so it can be easily carried anywhere.

Powering Your XM5

You have several options for powering your XM5:

  1. Optional Lithium-Ion FastCharge® System
  2. Alkaline non-rechargeable battery. You may also use an external power supply, to save battery life when listening at home.
  3. NiMH or NiCd rechargeable battery. These can only be recharged OUTSIDE of the XM5.
  4. Lithium NON-rechargeable battery. These are usually 9.6V, and have a very long life.


  1. Optional Lithium-Ion FastCharge® System: If you ordered your XM5 with the Lithium-Ion FastCharge system, just plug in the external charger to charge the battery.

    • The battery will fully charge in approximately 1.5hours. When charging is complete, the LED on the charger will turn from red to green.
    • The battery will charge even if the XM5 is turned on.
    • You can leave the charger connected indefinitely.
    • You can expect 30 to 40 hours of use per charge.
    • Your charger is a "World" charger - it will work with AC Mains voltages from 105 to 240 VAC, at 50 or 60Hz. If you are using the charger outside of North America, you may need a plug adapter (available from any local electronics store).

  2. Alkaline non-rechargeable battery. You can expect approximately 50 hours of use from a single Alkaline battery. You CANNOT use any type of external power supply when using an alkaline battery.

  3. NiMH or NiCd rechargeable battery A rechargeable NiMH or NiCd battery can be used. A NiMH or NiCd battery must be REMOVED from the XM5 to recharge. You CANNOT use any type of external power supply when using a NiMH or NiCd battery.

  4. Lithium NON-rechargeable battery. You can expect approximately 100 hours of use from a single Lithium Non-rechargeable battery. You CANNOT use any type of external power supply when using this battery.


To purchase the XM5, click here.


All contents Copyright © 2015 Practical Devices Corporation