Part 3: The Analog Audio Path
MIYO’s analog audio path is comprised of very high-quality components. Starting at the DAC, all volume attenuation is handled at the analog output, where we take the digital volume control from the OS and control the analog output level from the DAC. The eliminates any extraneous gain staging and potential issues arising from it, so right out of the gate, MIYO is treating your audio better than most.
That ability is one reason we selected the PCM1792A DAC. Of course the main reason is that in our humble opinion it’s the finest sounding DAC available today. We are pre-biasing the DAC output to force it into class-A operation. The DAC has crazy specs anyway, but this is a little trick to get rid of any residual crossover distortion.
From there, audio gets passed into the Texas Instruments OPA1664 opamp for both current-to-voltage conversion and anti-image filtering to the two headphone amps. This opamp has amazing performance, with extremely low noise and distortion, so that no coloration of the audio occurs at all. The entire signal path from the DAC output to the headphone amps is balanced.
The opamp passes audio to the headphone amps, which are truly remarkable. We’re using the Texas Instruments (noticing a trend here?) TPA6120 headphone amp, which is a current-feedback type amplifier. We run it on high voltage +/-15V rails (pretty sweet considering we’re on USB bus-power), and it delivers in every way – 128 dBA SNR, 112.5dB THD+N, 1300V/µs Slew rate – with great power at 80mW into 600 Ohms. The entire output path is DC-coupled. Offsets are servoed out using the DAC’s precision voltage reference (heavily filtered). Coupled with MIYO’s very high quality clocking and conversion, this translates into excellent dynamics and transient response, a lifelike 3D soundstage, and striking clarity – it’s your music the way it was meant to be heard.
The input side is treated with equal respect. We selected the PCM4220 for our ADC - another part which usually finds itself in high-end pro audio gear. Our analog input stage uses the fully differential THS4532 opamp - this allows us to cancel ground noise from the unbalanced input jack. We managed to incorporate gain and antialiasing filtering into a single stage, so this is the only amplifier between the input and the converter. The ADC is driven differentially by the amplifier stage to minimize noise and distortion.
We’re very particular about passive components in the audio path as well – we use 0.1% Metal Film resistors, and PPS Film and Niobium Oxide capacitors exclusively. All selected to be the lowest noise, lowest distortion, non-microphonic components available – no expense is spared.
To sum it up: the analog path is designed to take advantage of the digital side of MIYO as much as possible, making sure that the audio is the highest quality possible from end to end. And we believe the resulting sound is remarkable.