I just received a Khadas Tone2 Pro DAC/Amp in the mail today. It’s a diminutive USB, I2S, S/PDIF DAC based on the ES9038Q2M DAC chip and XMOS XU216 processor. It sports both single-ended and balanced outputs for both headphones (3.5mm TRS and 4.4mm Pentaconn) and fixed line out via novel hybrid balanced RCA jacks. It’s the smallest and least expensive full MQA Decoder DAC that I’m aware of.
I’ll reserve judgement on sound quality until I’ve had more time with it. I also want to try it in a couple of different systems with the recommended balanced RCA to XLR cables. However, so far, I’m certainly not hearing anything objectionable. Perhaps a little dark sounding fresh out of the box, that could be my ears today too (feeling a little stuffy).
This is not (yet) a Roon Tested DAC, but compatibility with Roon is great. The knob on the DAC can be used for play/pause/skip. I’ve verified that this works with Roon on macOS, but I’ve not attempted to set that up on my VitOS endpoint (probably requires Roon Extension Manager). I’ll be surprised if this does not work “out of the box” on RoPieee.
The rotary volume knob / controller only attenuates output from the headphones jacks; the RCA outputs are always fixed output. This seems like a reasonable decision, but it’s something to be aware of if you want to use it with powered monitors.
This is the first time that I’ve seen a USB-C style I2S input on a DAC. I’m not a huge fan of external I2S, but in the unlikely event that I can find a transport with compatible output, I’ll give it a try.
Fit and finish of the Tone2 Pro is very good. The volume knob is lightweight but has a nice feel. Pulling it forward twice to cycle through modes is a bit funky, as is the kaleidoscope of colors that indicate various operational settings and filters, but it all works as advertised.
The Tone2 Pro runs a bit warm. I measure a current draw of about 420 mA, so in spite of its small size, it will not be the best choice for a long flight (or even a long walk) as it will run down the battery in your phone rather quickly. Apart from that, it works fine as an OTG DAC with the supplied USB-C cable and USB Audio Player PRO, including MQA Decoding and Rendering.
The headphone amp has two gain settings, but with my 25Ω E-MU Wood Series headphones, I’m only able to raise the level up to 50% in low-gain mode before it’s thunderously loud. In spite of that, the amp is dead silent at low levels, so even high-efficiency IEMs should be fine.
Driving my 300Ω Sennheiser HD650 via the 4.4mm balanced output, I do have to rotate the volume knob past 50% in low-gain to achieve satisfying levels, but there’s still plenty of range remaining. I would not want to listen at 100% for more than a few seconds! In high-gain, it feels like there’s endless headroom. The manual does say that the maximum headphone impedance supported from the 3.5mm is 150Ω (300Ω via the 4.4mm Pentaconn). I’ve not tried my HD650s with a single-ended cable, but I’d be surprised if high-gain failed to provide adequate levels.
I’ll report back later once I’ve had a chance to try the DAC with the balanced RCA cables, but if you’re looking for a Roon compatible DAC/Amp with full MQA decoding, the Khadas Tone2 Pro seems like a solid choice based on my hour or two of playing with it.