Headphone amplifiers come in all sizes and at all prices, from inexpensive project-box designs such as the $129 JPS Labs O2 all the way up to state-of-the-art amplifiers such as the $3995 Audeze “The King.” Right near the middle of this range you’ll find the $1599 Dragon Inspire IHA-1 headphone amplifier, which is sold exclusively by Moon Audio. Created by Dennis Had, the founder of Cary Audio, who has been designing tube-based electronics for over fifty years, the IHA-1 began as a retirement hobby project. Mr. Had sold Cary Audio seven years ago and had planned to do a lot of relaxing and sailing, but after a year the lure of sailing was eclipsed by the siren song of Had’s studio space, where he began working on new single-ended tube designs. Eventually he turned his attention to headphone amplifiers, and the Inspire IHA-1 was born. While its price—especially for what is essentially a hand-built, made-to-order component—places the IHA-1 in the “affordable” category, its performance with the right headphones puts it firmly into the category of something you might buy if price was of no consequence.
The Dragon Inspire IHA-1 is a single-ended vacuum tube design that has its inputs directly coupled to the grids of two 6SN7 dual-triode tubes with only a selector switch and volume control between the inputs and the tubes. The IHA-1 has only three tubes total in its circuit, two 6SN7 dual triodes and one 5Y3GT rectifier. The IHA-1 can also be configured with different dual-triode tubes, such as a 6BL7 or 6BX7 (with the 6BX7 you lose some output power) and different rectifier tubes, including a 5Y3, 5U4, or a 274B. Because the 6SN7 tube is a dual triode, it allows the IHA-1 to have two gain stages, powered by each section of the 6SN7. While the IHA-1 is not a true dual-mono design because the right and left channels share the same power supply, the two channels remain separated throughout their signal path.
A set of special hand-wound, custom, air-gapped output transformers are also directly coupled to the IHA-1’s outputs. Because the IHA-1 is a direct-coupled design throughout without any coupling caps or output attenuation resistors in the signal path, it is more sensitive to EMF and EMI-generated hum and noise. “Purity at its best” comes at a price, which means you must pay attention to the IHA-1’s physical placement if you wish to hear it sans hum and extraneous noise.
The IHA-1 is also a zero-feedback design. According to the Moon Audio site, “THD is close to ultimate vacuum tube perfection considering zero feedback. The second and all remaining harmonic contents at the 1.125 watt output level into 32 ohms are over 65dB down.” But by eliminating feedback, the IHA-1 design also lacks the noise filtering that feedback can deliver; hence, the IHA-1 will be more sensitive to external noise either through the AC line or from other electronic devices.
The volume control for the IHA-1 is a 100k dual stepped attenuator made by a Danish firm, DACT. While this dual attenuator insures that both channels will track together accurately, it also eliminates the option of any channel balance adjustments. This is the sort of trade-off that was made to optimize the IHA-1’s sonic performance.
Readers may wonder how a single-ended tube amplifier that only supports single-ended inputs can supply a balanced headphone output. The “secret” to the IHA-1’s balanced output operation is that the secondary windings from the IHA-1’s custom air-core transformers are tapped to get the necessary inverted signal for balanced headphone operation.
Physical Setup and Ergonomics
The chassis of the IHA-1 measures 8 inches by 2½ inches (without tubes) by 10 inches, and is finished with a copper powder coat with a dual-process clear coat. The front panel has a volume knob on the left-hand side flanked by a three-way selector (Channel 1, Mute, and Channel 2) to its right. The right half of the IHA-1’s front panel has output connections for single-end ¼" stereo and four-pin XLR balanced headphones and a two-way toggle on/off switch. The back panel of the IHA-1 has two pairs of RCA inputs and one switched RCA output as well as the AC power connection.
The Inspire IHA-1 can be used both as a headphone amplifier and as a two-input analog preamplifier. The line-level output is an additional $100 upcharge over the $1599 base price, but it is an upgrade that vastly increases the IHA-1’s utility. I used both capacities during the review. For part of the review, the IHA-1 was attached to the analog output from a Grace m9xx DAC/pre, which was connected to my MacPro desktop. For some of my critical listening I used several high-performance portable players, including the Astell&Kern AK240, Calyx M, AR M2, Sony NW-ZX2, and Questyle QP1R. Because it has two selectable inputs you could easily set the IHA-1 up to handle both your computer and your portable devices as sources.
I also used a variety of headphones and in-ear monitors with the IHA-1. Since the IHA-1 has both single-ended ¼" and balanced headphone connections I also had the opportunity to compare the single-ended and balanced outputs on several headphones that have interchangeable cables, including the AudioQuest Nighthawk, Sennheiser HD700, and Audeze LCD-2.
My review sample came with two Sylvania 6NS7 dual triodes and one RCA 5U4 rectifier tube. These are the tubes that Moon Audio’s Drew Baird prefers, and they come at an extra cost of $200 (but you still receive the two stock 6SN7 Electro Harmonix and Sovtek 5Y3GT as well). I did not try “tube rolling” (changing out tubes), but obviously being able to use a variety of tubes is part of the appeal of the IHA-1.