HeadRoom is a unique company that has been dedicated to improving the headphone experience by providing hi-end headphone solutions to audiophiles everywhere. Based in Boseman, Montana, HeadRoom offers a full range of headphone products that includes not only headphones, but the important electronics that drive them. Their latest product is the BitHead, which actually includes a USB 1.1 interface geared towards portable laptop computers. If you've ever listened to a laptop computer then you are probably aware of the rather poor sounding audio that is available at the headphone output. This poor sound is not only a result of the DAC (digital-analog converter), but can also be attributed to the poor drive circuit that follows the conversion. The BitHead can work as either a simple amplifier or can completely replace the laptop's DAC by using the USB interface built into this unit. The USB interface receives S/PDIF data from the source and converts the digital PCM stream into two channel audio. The BitHead design can use internal batteries for reduced noise or can simply power itself from the USB interface. The package includes a variety of different feet for various mounting options. Velcro stickers attach the unit to your laptop or other portable device. Rubber feet are also provided as another option. A USB cable and mini-stereo cable are included with the unit.

Design
The BitHead makes use of some of the latest technology that includes a Burr-Brown (now Texas Instruments) PCM2902 chip. This integrated chip not only has a fully compliant USB 1.1 interface, but also includes a 16-bit stereo delta-sigma DAC and an ADC to boot. The PCM2902 has a built-in S/PDIF function that allows the BitHead to receive digital audio data directly over the USB interface to drive the internal DAC. The chip offers a signal-to-noise ratio of 89 dB with a THD+N of 0.01%. The user has the option of using the analog inputs on the BitHead to drive the headphones. The operational amplifiers used in the BitHead are the high-bandwidth LM6132B from National Semiconductor, which feature full rail-to-rail swing voltages and a high-slew rate (12 V/µS). Discrete output transistors are used to drive the headphone signals.

Construction
The plastic case is held together by three screws hidden beneath a rubber snap-on cover. Four "AAA" batteries power the unit for true portability. However, the unit can also be powered from the USB interface. The board design uses state-of-the-art surface-mount electronics, which results in a compact and low-noise design. There are two 1/8" headphones jacks with a single level control for both in the middle of the unit. There's a power switch located on the left side of the unit along with a green power LED. The red LED indicator lets you know when audio clipping is occurring. The process switch is used to engage the Audio Image Processor that can create a fuller sound on many recordings. I say "can" because there are times when I prefer not to engage it. In my opinion the sound enhancement varies widely with source material so it may or may not suit everyone equally. That said, it does offer a fuller sound to many recordings.

Performance
We listened to our Sony Vaio PCV-GRX550 laptop both with and without the BitHead amplifier installed driving a pair of Sennheiser HD 555 headphones. The difference was not subtle between the two setups. When listening to the laptop directly connected to headphones, the sound was thin and lacked bass. Inserting the BitHead between the laptop and headphones greatly improved the sound quality of the Vaio's analog outputs. We believe this was primarily due to poor drive electronics since the same DAC electronics is driving the high impedance BitHead unit.

We then inserted the USB connection into the laptop and our Windows XP found the appropriate driver so that the digital audio could be sent directly to the BitHead, bypassing the laptop's DAC and analog electronics. This resulted in a much cleaner sound with greater detail. The downside was a decrease in the maximum audio level. We didn't find this to be problem with our in-ear Shure E3c earphones, but with the HD 555 headphones, users may want more volume. Much has to do with the impedance of the headphones as well as the design of the transducers. In the case of the E3c design, the efficiency is higher, but not quite up to the sound quality we experienced with the HD 555. In addition, the high sensitivity of the E3c's made background noise in the BitHead more apparent. Volume levels are also affected by the current battery state. Lower battery voltages will result in the signal reaching a maximum level and ultimately clipping and turning on the red LED. This happened to us during our review. However, with low ambient background noise the HD 555 headphones provided adequate audio levels and sounded great.

Plugging the analog input back into the BitHead immediately bypasses the active digital USB link and enables the analog connection. Doing so doesn't seem to affect the digital connection and the computer continues to recognize the USB link. We also ran through some tests with our Neuros Digital Media Player and the results were also positive, but not quite as drastic as with our laptop. However, the audio definitely improved when using the BitHead as an audio amplifier.

Total BitHead Version
HeadRoom offers a higher performance version of the standard BitHead called the Total BitHead for an additional $70 (MSPR $269). In this version of the product, the National LM6132B opamps are replaced with the Burr Brown OPA4743 opamps. In addition, some of the resistors and capacitors in the signal path have been changed to higher quality devices. Standard resistors are changed to metal film versions and the ceramic capacitors are now film capacitors.

The sonic differences between the two BitHead models were subtle especially with our lower cost headphones. However, when using a pair of Sennheiser HD-600's, the difference between the two became somewhat more apparent with a smoother midrange revealed from the Total BitHead version. We feel that the Total BitHead will satisfy those audiophiles who want to squeeze the most out of their portable products. However, depending on the equipment used in the setup it may not be substantially different to justify the cost difference.

Conclusion
The BitHead and Total BitHead are nifty little products that offer audiophiles improved sound quality for laptops and other portable devices, even without the use of the USB interface. If you are unhappy with the sound of your laptop or portable device, it may be more than a lousy DAC. The BitHead definitely improved the sound quality of our portable products both in analog and digital modes, so it's certainly worth a try with HeadRoom's 30-day satisfaction guarantee.

- Kevin Nakano

Laptop: Sony - Vaio PCV-GRX550
Portable Player: Digital Innovations - Neuros II HD
Headphones: Sennheiser - HD 555, HD 600
Earphones: SHURE - E3c

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