In addition to certifying the performance of commercial cinemas and consumer audio and video products, THX also develops new technologies and licenses them to various manufacturers.
Among these new technologies is the company’s ultra-quiet AAA (Achromatic Audio Amplifier) power-amplifier design, which first appeared commercially in the Benchmark AHB2 in 2015.
Two years later, THX introduced the second generation of AAA technology, this time intended for headphone amps. I first heard some prototypes at CanJam SoCal 2017, and I was quite impressed. So, when Helm Audio announced at CES 2020 that it was implementing AAA technology in a mobile headphone amp, I immediately requested a review sample. Once the DB12 AAAmp finally arrived, it was well worth the wait.
The DB12 AAAmp is a small unit measuring 2.8 x 0.9 x 0.5 inches (LxWxH) and weighing only 1.08 ounces. A 12-inch cable emerging from one end terminates in a 3.5mm TRRS (tip-ring-ring-sleeve) male plug, while a 2-inch cable at the other end terminates in a 3.5mm TRRS female jack. Both cables are custom-shielded silver with molded strain relief.
Essentially, the DB12 is a powered headphone cable. As such, it relies on a physical connection at both ends. That means the source device must have a headphone output, which many smartphones and other mobile devices no longer have. If a device doesn’t have such an output, you will need an adapter for it.
The frequency response is specified from 20Hz to 20kHz (+0.01/-0.2 dB) with a 32-ohm load. The full-range gain is said to be +12 dB with an independent bass boost of an additional +6 dB for frequencies between 60 and 100Hz. When I asked why the boost was only down to 60Hz, I was informed, “The curve isn’t a bell and it’s not super sharp. It’s a shelf, and it does extend down to 20Hz.” I would recommend saying that in the product info. Output power is rated at 109 mW/channel into 16 ohms and 111 mW/channel into 32 ohms with <0.1% THD (total harmonic distortion).
Speaking of THD, it gets much better at lower output levels: 0.0008% (-102 dB) at 10 mW/16 ohms and 5 mW/32 ohms and 0.00035% (-109 dB) at 0.049 mW/10 kohms. Likewise, IMD (intermodulation distortion) is quite low: 0.03% (-70 dB) at 16 ohms and 0.01% (-80 dB) at 32 ohms and 10 kohms, all measured using the SMPTE standard 70Hz + 70kHz.
To achieve such low distortion levels, the THX AAA amplifier design uses a bipolar class-AB output stage with feedforward error correction to cancel zero-crossing errors. According to THX, this allows the amp to exceed the performance of class-A designs without their low efficiency, poor damping, and high power consumption. It also allows long battery life by reducing bias currents by a factor of 10 to 100 without increasing distortion.
The lithium-ion battery provides six to eight hours of playtime depending on the volume setting and whether or not bass boost is active. A USB-C port on one side of the unit lets you connect it to a USB power source to charge the battery. The specs say “2.5 hours fast charge, traditional charging time longer,” which means that a USB power adapter with an output of 9V/1.67A or 5V/2A can charge the device from empty to full in 2.5 hours, while an ordinary charger with 5V/1A output takes about four hours.
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