Aliexpress WM8740 dac/psu. This comes as two separate good quality metal cases, one containing the mains transformer and one containing the dac, both fitted with rubber feet. After failing to get the Audinst to work, I had to get this. This is purely a dac, you need a separate headphone amplifier to be able to listen to it. I bought the more expensive version with the Talema transformer, it wasn't much extra so I got the best one. This came from "hifidiy audio store", I don't know if they are anything to do with the chinese hifidiy website. It's a similar chipset to the hifidiy/aune mini usb dac V2, except they have replaced the BB PCM1793 with the Wolfson WM8740 as the main dac chip on the board. The USB interface is a PCM2704 again. The metal boxes are smaller than I expected, but they look well made and should last a while.
$ cat /dev/sndstat
Installed devices:
pcm0: <Conexant CX20590 (Analog 2.0+HP/2.0)> (play/rec)
pcm1: <Intel Cougar Point (HDMI/DP 8ch)> (play)
pcm2: <Intel Cougar Point (HDMI/DP 8ch)> (play)
pcm3: <Intel Cougar Point (HDMI/DP 8ch)> (play)
pcm4: <Burr-Brown from TI USB Audio DAC> (play) default
Works well with freebsd 14.4 on my thinkpad X220. Sounds very nice. Of course the better the headphone amp you have the better it will sound, it sounds very nice with the Cute Beyond. The output level from the dac is quite high, I set the CB's gain switch to "low" to get a reasonable range of adjustment on the volume pot.
Photo shows the power supply box on the table, the WM8740 dac above, and the CB headphone amp on top of that.
I took mine apart for a look at the circuit board, it looks reasonable. The solder side looks fine too, everything neatly soldered.
They've used a JRC 5532D in the filter/output stage, socketed (turned-pin socket - nice) so you can change the op-amp if you like. It sounds pretty good with the chip they have supplied though; I'm not really a fan of swapping op-amps, they are not really readily interchangable, it all depends on the circuit. Most components are still through-hole so its repairable, although they've shrunk the board, everything is miniature, you definitely need a fine-tipped iron to work on this. The connectors and switches look more or less ok, a bit cheap but what do you expect at the price, the only real disappointment was the output RCA sockets are only chrome, not gold plated. I guess they are feeling the pinch, even in Shenzhen. The lack of gold plating on the RCA sockets didn't seem to hurt the sound quality though. Hopefully this build is good enough to last a while, it should be fine for home use anyway. The electronics are fully enclosed in the metal boxes, there should not be much scope for ingress of dust or dirt. If the worst happens and anything starts smoking, it's enclosed in the aluminium box, but I think that is a very low risk. The electrolytic caps by the voltage regulators are Rubycons, which are good quality Japanese caps.
Putting the transformer in a separate metal case shields the rest of the circuit from mains hum, and even with the two cases mounted on top of each other as in the photo I could hear no hum at all in the headphones, with the volume on the amp turned up to 11. The connecting cable from the transformer box to the dac is 1m long, so the transformer box can be sited remotely from the dac box if desired, for further isolation from the transformer. There was also no hiss noise audible in the headphones at all at maximum volume with no music signal, all very good. I also tried listening to silence here :-
View: https://www.youtube.com/watch?v=_VUKfrA9oLQ
and again, I was unable to hear any hum or hiss in the headphones with volume set to max. So its pretty good.
I measured the DC offset at the two RCA outputs, the left hand channel was 0 mV which is perfect, while the right hand channel had a +4 mV DC offset, not perfect but still pretty good. My meter claims to be accurate to within +/- 1 mV (if I can believe that). There is a discussion below of how much DC offset is acceptable from a line level output, received wisdom is anything <50 mV is acceptable for audio, whereas <5 mV is preferable and 0V is perfect. So this dac appears to be fine. Of course I don't have any proper audio test equipment so this review is only a basic check.
So I broke out my PPA today after having it sit on the shelf for a long time because one of my coworkers wants to see it and run some test on it. I took the time to check it to make sure it was still in spec. All good, the outputs have 1.5mV or less DC offset, the biasing on the opamps is...
www.head-fi.org
It sounds excellent, anyway, this is another good one. It's definitely musical, the wolfson chip is capable of good results. Good bass extension and very sweet midrange, wide sound stage, and not tiring to listen to. I think this sounds better on freebsd than my Audinst HUD-MX1 (another WM8740 design) sounds on linux. In fact I think this one sounds just about on par with my Burr-Brown Aune V2, although the build quality of the Aune is much higher, but that was made 15 years ago when stuff was a lot cheaper than now. I think the era of getting well-made stuff from Shenzhen for ridiculously cheap prices lies 10-15 years in the past now, their costs have gone up a lot, and inflation has eroded the value of our money. But perhaps the circuits are a bit better designed now, and hopefully there are fewer fake components. I would buy this one again, anyway. I paid 86 GBP (which is quite a lot, compared to the prices years ago) and a further 20 for postage, it's quite a heavy package. It took about a week to get here, it was well-packaged and worked as soon as I plugged it in with no problems.
There is a datasheet for the WM8740 here
https://www.mouser.com/datasheet/2/76/WM8740_v4.4-532395.pdf
and for the JRC 5532 dual op-amp here
https://datasheet4u.com/datasheets/JRC/JRC5532/788679
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