HPA-1 Headphone Amplifier - PREORDERTom Christiansen Audio
The HPA-1 is expected in stock by early-to-mid December, 2019. The preorder discount is my way of thanking you for your patience and support. Note, however, that the discounted price will only apply for the first 40 preorders. The preorder sale will end once the first 40 HPA-1s have sold, or when the HPA-1 arrives from assembly, whichever occurs first.
Key Features of the HPA-1
- World class performance as characterized by ultra-low harmonic distortion, extraordinarily low intermodulation distortion, and ultra-low noise floor.
- Two inputs: XLR (balanced) and RCA (unbalanced), selectable by front-panel switch.
- One output: ¼" (6.3 mm) phone jack.
- Two gain settings: 0 dB (1×) and 12 dB (4×) to accommodate sources ranging from balanced pro/studio sources to media players, phones, and tablets. The gain is selected by a switch on the front panel.
- Protection against excessive DC voltage on the amplifier output. This protects your headphones in the case of a catastrophic amplifier failure.
The HPA-1 delivers true world class performance at a very attractive price. It provides up to 1.0 W (1000 mW) of output power at ultra-low harmonic distortion, exceptionally low intermodulation distortion, with an ultra-low noise floor. It is mainly due to its exemplary performance on these parameters that the HPA-1 is able to reproduce the music exactly like the artists and recording engineers intended.
The ultra-low distortion results in a clean and crisp sound. This is especially evident in the rendition of instruments that challenge many ordinary amplifiers. This includes instruments such as cymbals, hi-hats, snare drums, and saxophones, which the HPA-1 renders superbly. The ultra-low distortion design of the HPA-1 also allows you to hear the sounds normally only experienced in live performances, such as the body cavity resonance of an acoustic guitar on the leading edge of the string attack.
It is noteworthy, that high levels of intermodulation distortion have been associated with the activation of the fight-or-flight response in humans. Thus, it stands to reason that a low level of intermodulation distortion is crucial to a pleasant listening experience. This is another area where the HPA-1 excels. Thanks to its extremely low intermodulation distortion – in particular on multi-tone tests – the HPA-1 renders the music with an incredible realism and an amazing sound stage without resulting in listening fatigue.
Finally, the ultra-low noise floor of the HPA-1 is responsible for the complete absence of sound during pauses in the music – even when used with sensitive in-ear modules.
The HPA-1 is designed and manufactured in Canada. The raw circuit board is made in Ontario. The PCB assembly is performed in Calgary. The chassis is made in Japan with some mechanical parts sourced locally from Calgary.
A summary of the HPA-1 specifications is provided in the table below. Download the full specifications and performance graphs for the Prototype (Rev. 1.1) here:
|Output Power||1.0 W||20 Ω|
|Output Power||1.0 W||32 Ω|
|Output Power||250 mW||300 Ω|
|Total Harmonic Distortion (THD)||< -130 dB||300 Ω, 100 mW, 1 kHz|
|Total Harmonic Distortion + Noise (THD+N)||
|300 Ω, 100 mW, 1 kHz|
|Intermodulation Distortion (IMD)||< -112 dB||18+19 kHz @ 1:1, 300 Ω, 100 mW|
|Multi-Tone Intermodulation Residual||<- 140 dBr||AP 32-tone, 300 Ω, 100 mW|
0 dB (1x)
+12 dB (4x)
|Selectable by switch|
|Input Sensitivity||2.8/0.7 V RMS||Low/High Gain, 32 Ω, 200 mW|
|Output Impedance||35 mΩ||1 kHz|
|Channel Separation||95 dB||1 kHz|
|Dynamic Range (AES17)||130 dB|
|Signal-to-Noise Ratio||132 dB|
|Residual Mains Hum & Noise||1.25 µV RMS||A-weighted|
|Mains Voltage Requirements||
80–264 V AC
|Size||140 x 55 x 210 mm||(W x H x D)|
|Designed and Manufactured in Canada|
These specifications were derived from measurements of the HPA-1 Prototype (Rev. 1.1). They are subject to change (and are expected to be slightly better in the final revision).
The signal path of the HPA-1 is balanced all the way to the volume control. Only the last ~40 mm of the signal path from the volume control to the output is single-ended. This ensures the best immunity against interference from mains hum and other interference sources.
The output stage of the HPA-1 is a high-speed, high-current, current feedback operational amplifier with extremely low intrinsic distortion. To further increase the performance of the output stage, the HPA-1 uses a precision audio opamp to perform error correction on the output stage. The HPA-1 reaches its stellar performance level, in part, due to the use of this error correcting architecture. It is also due to this architecture that the HPA-1 is free of any sonic signature of its own, thereby allowing you to hear the music the way the artists and recording engineers intended it.
The block diagram of the HPA-1 is illustrated below.
[IMAGE TO COME]
The circuit board layout has been optimized for audio performance. Thus, the circuit board is a 4-layer PCB, which features the elaborate use of planes and pours to minimize the error voltages that develop across the various signal conductors and ground connections. The circuit uses Susumu RG-series precision metal film resistors with ±0.1 % tolerance at critical nodes in the circuit. The only capacitors in the signal path are two Nichicon MUSE UES-series bipolar capacitors. They make no measurable contribution to the sonic signature of the HPA-1.