Product Review (May 2010) HeadRoom
Micro DAC and Micro Amp Headphone Amplifier

By Kevin Nakano


HeadRoom Micro DAC and Micro AmpHeadRoom has been providing audiophiles and music lovers with a wide range of great sounding headphone products for years. Their products include everything from a $99 battery operated headphone amplifier to a full blown $1700 pair of Desktop Bi-Amplifiers. HeadRoom has remained dedicated to improving the headphone experience and with that comes unparalleled experience with design topologies that provide the ultimate headphone experience. Over the years, HeadRoom has expanded what they offer and now sells a variety of headphone related products and accessories. This review will cover HeadRoom's Micro DAC and Micro Amp products, each priced at a moderate $349. This combo offers an affordable way to get audiophile sound quality on a budget. The versatile Micro DAC is designed to work with the Micro Amp, resulting in a low compromise, high performance headphone system.


HeadRoom Power SupplyLinear Power Supply
The external power supply included with both the Micro DAC and Micro Amp provides clean DC regulated power with low noise. This power adapter features a conventional power transformer with a full wave bridge rectifier circuit feeding a pair of 2200 uF/25V filter capacitors. Linear voltage regulators, an L7815 (+15V) and an L7915 (-15V), produce clean DC to the Micro DAC and Micro Amp units. Each voltage output is rated at 0.24 amps. The AC cord is about 2-feet long, whereas the DC power cable with the high quality 5-pin DIN connector is about 6-feet in length.


HeadRoom Micro DACMicro DAC
The Micro DAC is a D/A converter that features three ways to digitally connect to music sources. A USB input, toslink (optical) or coaxial S/PDIF input is provided. The coaxial digital input uses a standard 3.5mm jack instead of the more typical RCA jack, so an adapter cable may be required. The three-way switch on the front panel selects between the three digital inputs. The output of the Micro DAC is a line level audio signal that requires a separate amplifier. In our case we have the Micro Amp to mate to the it. There is no reason why this Micro DAC cannot be used with a home audio system as well. The front panel looks simple, but the real power of the Micro DAC lies in the internal design. HeadRoom has always made impressive electronics that audio engineers can drool over, and this product is no different.

Headroom MicroDACInside the Micro DAC
The Micro DAC is packed with state-of-the-art digital and mixed-signal audio chips providing the ultimate in performance. Digital audio sources are handled by a Cirrus Logic CS8416 Digital Audio Interface Receiver accepting digital audio from the Burr Brown (now TI) PCM2902E USB interface chip, toslink input, and the coaxial input. This digital audio receiver is an industry standard and follows a lineage of excellent performers. Once the digital input is selected it goes to a Cirrus Logic CS4398 D/A converter that is specified with a dynamic range of 120dB with a THD+Noise of -107dB.
The audio output stage uses an independent Burr Brown OPA134 opamp on each channel to drive the line level output. The OPA134 series are ultra-low distortion, low noise operational amplifiers that feature a true FET input stage resulting in superior sound quality and speed with exceptional audio performance. Input power comes from an outboard linear power supply that provides fully regulated +/- 15 VDC though the DIN connector. A long 6-foot cable extends from the linear power adapter. Six 470uF/25V capacitors provide bulk power reserve along with six large surface mount capacitors. The signal chain utilizes low drift, 0.1% metal film resistors and ultra-low ESR polyphenylene-sulfide film capacitors for superior audio performance. The internal design of the Micro DAC speaks for itself.


HeadRoom Micro AmpMicro Amp
Unlike the Micro DAC, the Micro Amp does not do any digital processing and handles all the audio in the analog domain. Two 3.5mm analog inputs are selectable with the front panel switch. There is also a volume controlled level output.
The Micro Amp is designed to drive serious headphone loads.

HeadRoom MicroAmp BoardInside the Micro Amp
The Micro Amp circuit board uses four 470uF/25V filter capacitors and includes four additional bulk surface mount capacitors located next to each bi-polar output device. Each audio channel has a dedicated set of Burr Brown (TI) OPA134 ultra-low distortion, low noise operational amplifiers. Both the Crossfeed and Gain circuits are fully analog designs that use these opamps. The output stage on the Micro Amp uses a complementary pair of MJD243 (NPN) and MJD253 (PNP) 4A, 100V bipolar transistors. These output devices are biased to virtually eliminate crossover distortion. Based on my calculation, these devices are dissipating just over one watt idling. Each channel has an independent trimpot for adjusting the bias level. There are also a set of test points that are used to measure the bias level when setting the idle (bias) current through the output devices. This is a feature usually only found on power amplifiers, so we were pleased to see that HeadRoom included this capability in a headphone amplifier that normally drives much higher impedances. In other words, some may call it overkill, but audiophiles call it nirvana. The design is impressive and the board layout is very clean - a common attribute of HeadRoom products.

HeadRoom Micro Amp OutputNo Crossover Distortion
One of the benefits of running the output stage of the Micro Amp at a relatively high bias level is the elimination of crossover distortion as the output transitions from a positive signal to a negative signal and vice versa. Crossover distortion occurs when one output device begins to hand-off the current to the other output device and both devices are in a state of little or no current. By driving the bias current higher, the zero-crossing transition becomes less apparent and results in less distortion in the audio signal. Even with a good load placed on the output (we used the UE Custom 11 Pro monitors) of the Micro Amp, there is no distortion that can been seen on the scope.


HeadRoom Micro DAC USB InterfaceSetup
The Micro DAC and Micro Amp are the exact same dimensions and feature a tongue and groove design that allows the units to be stacked on top of one another in a secure fashion. This works well and still offers a compact footprint when sitting on a desktop. A simple 3.5mm male-to-male cable was used to connect the line level output on the Micro DAC to Input 1 of the Micro Amp. Once the Micro DAC was connected to our laptop using a USB cable, it appeared in the Sound section under the Control Panel and was identified as Speakers. The Micro DAC did not require any special drivers on our Vista-based machine. We set the Micro DAC as the default playback device before running any tests and it worked flawlessly during our tests.


Sennheiser HD600 Headphones
Ultimate Ears Custom 11 Pro Monitors

Performance
Most of my listening involved an HP Pavilion dv7 laptop as a source with the USB port streaming digital content to the Micro DAC. I was astonished by just how good this two piece system sounded as I listened through a pair of Sennheiser HD600 headphones. The same was true when I played audio though my custom Ultimate Ears Custom 11 Pro in-ear monitors. The Micro DAC produced clean articulate audio from a variety of my favorite sources and the Micro Amp played it effortlessly through the HD600 headphones and Custom 11 Pro monitors. Something very different with the HeadRoom system is the ability to drive the HD600 headphones to much higher levels than I have experience in the past with outboard headphone amplifiers. In fact, the Micro Amp includes a three position level switch on the front, which helps the user dial in the desired volume range. In most instances I had this gain switch in the medium position with ample volume still available. The UE Custom 11 Pro in-ear monitors are even more sensitive, so I used the low setting. This is something other DAC/Amp systems cannot achieve simply because they are powered from batteries or use the 5V USB port and require a DC charge pump or similar technique to raise the rail voltages on the output stage to achieve reasonable drive levels. In doing so, there is a limitation on supply current that can have an affect the audio performance. In addition, switching is usually involved to pump the voltage up and this can also have an impact on sound quality. Alternatively, the Micro Amp uses a robust external +/-15V linear regulated power supply rather than relying on rail voltages from an internally generated circuit. This allows the Micro Amp to provide a "higher-end" output stage topology with Class A biasing and no cross-over distortion. The sonic difference was apparent with the Micro DAC and Micro Amp combo and it has become our favorite combo for our headphones.

Chesky - Livingston Taylor Music
Some of our favorite reference music comes from Chesky recordings. Many of these discs have pristine sound quality that can help reveal subtle differences in the analog chain. Using the Sennheiser HD600 headphones, I listened to several songs including the first track of Livingston Taylor's Ink DVD - Isn't She Lovely. This is a well made recording with excellent resolution and good dynamics. The singer's deep vocals along with his fine acoustic guitar textures provided excellent source material. The sounds of strings being plucked along with harmonizing on certain chords provided an excellent example of just what this DAC is capable of reproducing. What I really liked about this setup is the ability to drive the headphones effortlessly to levels not possible with many other products I have used.

All of my MP3 recordings stream at 320 kb/s to minimize compression artifacts and are mainly played through our Sonos multi-room music system or on portable media devices (iPod and Zune). Interestingly enough, there was significantly more detail that could be heard when listening with my Sennheiser HD600 headphones through this HeadRoom combo. I could hear the noise floor change slightly as the as the sound engineer increased a guitar or drum track into the main recording. I don't ever recall ever being able to discern this level of detail on these recordings.


HeadRoom Micro DAC Package HeadRoom Micro Amp Package
HeadRoom Micro DAC
HeadRoom Micro Amp

Conclusion
The Micro DAC and Micro Amp is a combo that I can wholeheartedly recommend to audiophiles wanting more from their headphone experience. The Micro DAC and Micro Amp are partitioned in a way that resembles the days of well built components, where users would refuse to compromise sound quality for convenience. Those who already own a favorite DAC can still add the Micro Amp to the back end of their signal chain and get a great sonic benefit.
The Micro Amp is warm to touch due to the higher than normal biasing needed for the Class A operation of the output devices, but is an attribute of the incredible sound quality associated with this.

The external dual voltage power supplies are a bit bulky (quiet linear designs), but the long 6-foot cords allow them to be placed away from the Micro DAC and Micro Amp units. The power connectors used on both of these products are excellent and provide a solid and reliable connection that is so unlike today's cheap electronics. HeadRoom also offers a full 2-year warranty on the products with a 30-day Satisfaction Guarantee . As of this writing, HeadRoom is currently offering free shipping on all orders. The only way to experience this system is to get it into your own listening environment with familiar music. HeadRoom's 30-day guarantee makes that decision pretty easy.

- Kevin Nakano





OPPO BDP-103 Blu-ray Player




Review System

Laptop: HP - Pavilion DV7-1245DX Laptop running Windows Vista 64-bit
Headphones:
Sennheiser - HD600

Monitors: Ultimate Ears Custom 11 Pro
Oscilloscope: Tektronix 2245A 100MHz Analog 4-Channel Oscilloscope


Review - At a glance


Headroom - Micro DAC and Micro Amp Combo


Micro DAC Features:

  • Produces high-fidelity audio from digital signal sources.
  • Stacks securely and neatly on the Micro Amp; a perfect pairing!
  • Accepts all valid S/PDIF formats and rate; accepts USB to 16/44.1kHz
  • Inputs selected from front panel three-position switch.
  • Power indicator

    Micro DAC DAC Manual

    Micro DAC DAC Set Up


Micro Amp Features:

  • Delivers high fidelity headphone audio with discrete component Jung diamond buffer output amp.
  • Improves headphone imaging with HeadRoom's famous crossfeed circuit.
  • Gain switch optimizes amp for headphones of different efficiencies.
  • Switches between two analog line inputs.
  • Includes volume controlled pre-amp out for desktop speakers.
  • Produces high-fidelity audio from digital signal sources.
  • Power indicator

    Micro Amp Manual

    Micro Amp Set Up


Company Information
HeadRoom Corporation
2020 Gilkerson Drive
Bozeman, MT 59715
Toll Free: 800-828-8184
Phone: 406-587-9466
Fax: 406-587-9484
Website: www.headphone.com

Model: Micro DAC
Source: Manufacturer Supplied
MSRP: $349
Size: 4.5"(11.5cm)x 3.5"(9 cm) x 1.5"(3.8cm)
Weight: 8.4oz (238 grams)

Model: Micro Amp
Source: Manufacturer Supplied
MSRP: $349
Size: 4.5"(11.5cm)x 3.5"(9 cm) x 1.5"(3.8cm)
Weight: 8.8oz (250 grams)

Warranty: 2 years with 30-day Satisfaction Guarantee


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