Useful, but this is squarely aimed at gamers. Software is Windows-only. Hopefully it can be had for no more than $50.

If the headphone port is TRRS, why not just put two on it, for 2x headphones or headphone + line out.

TiggerIf the headphone port is TRRS, why not just put two on it, for 2x headphones or headphone + line out.

So, this thing is running a Cmedia CM108-B. This is a pretty standard dongle DAC. Lets look inside.


Couple of interesting things here. It is dual-DAC... which you would think means dual-output, but often this is done for better performance from the chips... separate left and right. Better channel separation/crosstalk. There's a lot of talk on the actual value of doing things that way, and I'm not up on why it's done on such small circuits. Maybe because they're cheap and adding a second gives slightly better numbers? Maybe related to spacial processing features for headphones? Better voltage swing behavior? Impedance for line-level vs headphone? Maybe those things are more of an issue on this scale, or the DAC topography chosen simply has poor stereo performance. Eh... there they are, regardless. Dual-mono DACs. You see the outputs of the two designated "LOR" and "LOL" - line output left and right. Further down, you see the ADC for the mic input.

I suppose each DAC could drive a headset on its own... but that might be another reason to split by channel... more power output from the individual DACs. It could have the effect of summed balanced-output, but the other way around. Instead of double-amplification, you get split-amplification. I mean, with that, we get a whopping 50mw of max power on a 1v chip amp. Many smartphones today do better! This thing can basically only handle easy to drive stuff with lower impedances to begin with. Interestingly, speaker-mode runs just a single DAC in stereo... probably for efficiency, but the whys and hows are anyone's guess. Maybe just cause it's an unbalanced line-level output and they can fork off one because they run differential DACs. If this functionality can be expanded by added processing and an external EEPROM, not for me to say. I don't engineer the damned things. But out of the box, this is all that it can do. It does either headsets or speakers, not both, or even two of each. And even the ADC gets disabled in speaker mode. Playback-only. There's one pin on the chip for it. High or low input on that one pin determines all of this. That's right in the DAC chips they are using. Again, you could build fancy modules with some external ROM trickery to get around it, and that costs 3X as much in the end. Or get an audio package that already does it for 2x the cost on the product. Not happenin on a lil guy like this.

The only way I could see to accomplish it is with daisy chaining. Two jacks share output. Potential split impedance load though. Ghetto. To do it right, you need circuitry to offset that so you don't have weird sound glitches and volume mismatches. Make it one load for the audio package on the other end. Otherwise, you may as well buy a y-splitter and call it a day with this thing. The dinky stuff in there probably isn't going to like the current load though - now you need a discreet opamp package.

Problem solved right there. Opamps for each one man! It seems like almost none of these USB trinkets have any added amplification outside of the "DAC" which is in actuality an integrated audio package that also provides basic output. The DACs are inside of that chip. Plenty of 1-chipper amps to make simple but decently powerful output sections with. They've been around forever and you can get better output impedances, generally. Can't find a figure but I'm almost betting this is one of those with a 32ohm output on it - I have a superstition that this is part of what made old mobos sound crummy, even if they measured well. Put a dynamic load on em and the frequency response craps out because the impedance ratio is way off. I hate this crap lol. Why don't any of these things have any proper power? Give them SOMETHING, I mean dang man! It's bottom-level portable audio in this thing. But somehow I'm betting it's common in products like these...

Datasheet for anyone curious.
dtsheet.com/doc/951434/etc-cm108


Honestly, I just came back to this post to say that I don't think this thing is great. I mean, I'm not hot on the tail of what hardware goes into these things, but this is pretty anemic at just 50mw (average, I'm assuming since impedance isn't noted.) With only 1v on tap you can forget about high-impedance. That's why it gives an 80 ohm upper limit. I wonder how much of that 50mw it's even getting out by then, you know? Is that 50mw rating at the top of its impedance range? Or the bottom, 16 ohms? If bottom, it's god awful. My god, that's sad. If top, it's only sort of bad. If average, man I dunno. Should be pushin double that at typical loads for these cans, at least. The tiny desktop units (like, maybe double the size) can pump upwards of 300mw in to 20 ohms and generally have better features. They may be getting close to 50mw at 300, which with good sensitivity, will still be "enough." The output capabilities aren't exactly spectacular with this thing, either. This is get-the-job-done. Basic 16-bit/48khz. That's not bad in itself, but most modern DAC designs are doing more... and the older ones generally don't sound that good, and not because of the max bit-res or sample rate. The EQ and 7.1 are on-chip gimmicks, to me. Nice, I'm sure, but it's all there already, they just add a driver and an interface to support it. Gotta be a cheapie. It's VERY rudimentary, performance-wise. Not to say that it's bad... but the jacks out of the motherboard stand a good chance of being better than this thing these days... the main advantages might be noise and tactile controls. That's pretty much what it is. A very basic thumbstick dac with a wire and some buttons.

Why is it that so often the 'G' in "Gaming" stands for "Gimped?"