So maybe I don't have anything sensitive enough to get noise @ 80, but I did have some noise @ volume settings over 100-120 depending on the headphone, also can hear clicks as it changes volume settings as you approach 127. Those settings would have been painfully loud if it was playing something so I don't really mind that personally. On a related note I was thinking this really doesn't get that loud until I saw the volume goes past 100 :/ I'm not really sure why they went 0-127 instead of 0-255, I assume it still represents mute -> -95.5dB -> +31.5dB. Maybe because of how many turns it already takes to go from 0-127? I think it was maybe worse on the SE output but I only tried 1 set of iems on both inputs.
At max volume on the se output my iem made like a foghorn noise which is kinda bad but I think they would have been in danger of being damaged had audio been playing, there's almost no chance of accidentally going to max volume though. None of the other hps did the same just a hiss @ max on the 4.4mm but that one iem I used se is also my most sensitive headphone at 107db @1mw.
I couldn't detect any noise on the line out. Maybe the noise is coming from the pga2311s at high gain? I dunno really... but it drove all my hps quite loud before getting to where I could hear the noise, though I don't have anything extravagantly sensitive or not sensitive.
The knob feels like metal to me... it's cold to the touch when it's not warm from being used, though I can't be certain without doing something destructive. As far as I can tell the only external plastic parts are the led lenses.
Agree that the gain settings aren't that different like maybe +6db per setting or something, maybe I will check the voltage change :/ I actually tried to take it apart but I couldn't get much further than taking the back panel off. No idea how to remove the knob, the pcb is wider than the hole. I don't know how I could take it apart further without breaking it.
I have an SMSL M500(that's gonna be confusing :/) that struggles with me changing playback khz / dsd rates sometimes and I wasn't sure if it was my transport or not but i'm pretty sure it's the usb implementation in the M500 now (I've installed the latest firmware on their website). I didn't have this issue at all with the M400(YinLuMei). I personally don't use MQA just flac and dsd so no comment on how well that works on the M500 or if it's supported on M400 (I assume no?)
Battery lasted me 5:34 with the 4.4mm jack volume 70 to 85. I would say my main complaints are the battery life and the fingerprint side~ but still would seem to indicate that the hp amps are biased into class a?
All this is mostly technical stuff but still listening, what I hear so far still sounds good. I don't have other portable dacs and such to compare to or the one I have is 10+ years old and just not as good. Fairly subtle differences between it and my desktop dacs but the HP out is better than them. (M500, zodiac+, my friend who rents my basement and therefore is my quarantine buddy will have a d90 to compare with shortly.) The zodiac is in my speaker system so slightly annoying to compare vs but will try with speakers later. Anyhow the treble seems less sibilant than the m500. I think the m500 is a little sibilant which some might like, but I prefer the m400 in this regard. (Comparing the hp outs anyhow I think the m400 has a superior hp section anyhow so maybe that is skewing things, will compare them using the line out or using the 4.4mm as a balanced out, matching levels with voltage, then through a hp amp later.) Bass presentation is very good IMO.
