Outboard DACs

As Klipsch's Heritage headphone amp is both a DAC/preamp and headphone amplifier, its technical performance is also a story of two halves. Used as a DAC via either S/PDIF or USB inputs, jitter is extremely low at <10psec at all sample rates up to 192kHz. Its (fixed) output is 1.82V (re. 0dBFs) with a wide 108.5dB A-wtd S/N ratio and distortion that holds to 0.00045-0.0055% at peak (0dBFs) digital levels before falling back to a minimum of 0.0002-0.0008% (20Hz-20kHz) over the top 20dB of its dynamic range [see Graph 2]. Note that this output is phase inverted. The DAC employs a conventional linear phase digital filter offering 83dB of stopband rejection and a response that reaches out to –0.05dB/20kHz with CD/48kHz media, –0.6dB/45kHz and –3.5dB/90kHz (96kHz and 192kHz files).

The integral TI TPA6120A2 amp is very capable, offering a combination of low residual noise (–99.3dBV) and a low source impedance of ~0.4ohm in Hi-Z (Z = headphone impedance) and ~0.5ohm in Low-Z mode. Klipsch's literature tells you to 'Flip the gain switch to “Hi-Z” for a +10dB boost in output to drive even the most demanding headphones', but while the overall gain does increase from +1.9dB (Low) to +11.8dB (High) there's no fundamental difference in either distortion, frequency response or power output. Sure, into very high impedance (>600ohm) 'phones the maximum voltage output increases from 6.1V (Low) to 7V (High) but the generous 1065mW/25ohm and 880mW/8ohm power output is unchanged [Graph 1]. Distortion is very low at 0.00035-0.002% (20Hz-20kHz) but increases slightly through bass and midrange into lower impedance loads (up to 0.03%/20Hz at 10mW/25ohm). The response is very extended, with –0.5dB at 5Hz-100kHz. PM

Maximum output (<1% THD, DAC/Pre): 1.82Vrms at 421-437ohm
Max. output (<1% THD, headphone): 7.0V/600ohm / 1065mW/25ohm
Headphone Output Imp. (20Hz-20kHz): 0.37–0.52ohm
A-wtd S/N ratio (S/PDIF / USB / headph.): 108.6dB / 108.5dB / 100.3dB
Distortion (20Hz-20kHz, DAC/headph.): 0.0004-0.006% / 0.0015-0.03%
Freq. resp. (20kHz/45kHz/90kHz, DAC): +0.0dB to –0.0dB/ –0.6dB / –3.5dB
Freq. resp. (20kHz/100kHz, headph.): +0.0dB to –0.03dB/–0.55dB
Power consumption: 5W
Dimensions (WHD) / Weight: 200x58x145mm / 0.77kg
Price: £520