Outboard DACs

For this cost-effective product, EarMen has chosen a combined USB DAC/headphone amp IC from favoured Korean brand ESS – the ES9280PRO – supplemented here with a beefed-up analogue amp based on two TPA6120 op-amps from TI. The DAC IC includes three preset digital filters and built-in DSP that will host custom filter algorithms, but rather than baffle the user with a host of alternate linear phase, minimum phase, apodising, brickwall, etc, offerings, the ST-Amp is equipped with a one-size-fits-all hybrid type filter that combines limited pre-ringing with more extended post-ringing. Tested via its line outs, stopband rejection is a good 80dB but the response drops steeply above 18kHz with CD media to –4dB/19kHz and –12.3dB/20kHz (or –1.0dB/20kHz with 48kHz files). Furthermore, while the ST-Amp's USB input is rated to accept DSD128 and LPCM up to 384kHz/32-bit, in practice all high rate streams are downsampled to 96kHz and an analogue frequency response of –5dB/40kHz to –23.7dB/45kHz.

THD falls to a minimum of 0.00028-0.0018% (20Hz-20kHz) over the top 20dB of its dynamic range [see Graph 1] and while digital jitter suppression is not state-of-the-art, its figures of ~90psec (48-96kHz data) are still perfectly acceptable. Clock phase noise is very low and the sidebands are principally PSU- and data-related in nature [see Graph 2]. Otherwise EarMen has set its maximum single-ended output at a generous 4.15V (re. 0dBFs in), driven via a moderate 193ohm source impedance, to yield a very wide 113.3dB A-wtd S/N ratio and excellent low-level resolution good to ±0.3dB over a full 110dB dynamic range. If you are not obsessed with streaming >96kHz media over USB then the ST-Amp makes for a fine desktop DAC/preamp solution, especially with its analogue volume control. PM