FW13 AMD headphone jack has ~50 ohm output impedance?

I plugged my IEMs into my new Framework and noticed they were sounding way bassier than usual. After ruling out OS audio processing, I tried measuring the output impedance to see if that was the culprit. I played a sine wave at a lower level (to not overload the amp) and measured the output unloaded and across a 30-ohm load.

Correct me if I’m wrong, but
50mv unloaded
18mv loaded with 30 ohm resistor
30 * (50/18-1) = 53.3 ohms output impedance.

Honestly pretty disappointing. I was hoping I wouldn’t have to sacrifice a whole USB port just to get a usable audio output for my cheap IEMs.

For those that don’t know why, any headphone with a low, non-flat impedance curve will have an altered frequency response (it’ll sound different) due to the changing ratio between the amplifier’s output impedance and the load impedance at different frequencies. This primarily includes a large variety of IEMs that use balanced armature drivers, or have multiple drivers with a crossover. A good headphone amplifier should have output impedance below 1 ohm.

Update: Just borrowed the FW13 AMD I got for my dad this Christmas to measure the headphone jack, and got the same result.

I wonder how feasible it would be to get a USB+headphone jack module. Like Dual USB-C Expansion Card - #320 by tbe, but with x1 USB-C and x1 3.5mm.

Although I guess it wouldn’t help with your desire for high-quality audio unless you could package a decent DAC into the expansion card, too. At first I was more thinking about the Framework 16 which doesn’t have an aux port at all.

Ooh, that is a good thought. It shouldn’t be too hard, considering a decent audio circuit can fit into the space of a USB plug:

I’m certainly not expecting high power output in this form factor, but my baseline for acceptable headphone output has been the Apple USB-C to 3.5mm adapter. It does 1v into 32 ohm without trouble, and has output impedance of 0.3 ohms for about $10.

This would be cool for FW16 owners as well, since it would free up an expansion slot.

Hopefully FW will iterate on this and improve, or remove the built in audio jack from future models. Seems silly to have two.

FW16 has the 3.5mm removed. Your wish has been granted lol.

Fair enough

As far as I can tell the fw 13 has the audio bit on a separate board so it would be possible to make a custom one with whatever impedance you like.

No need to waste an expansion card slot for that.

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I think I recall the actual audio DAC being on the motherboard. Checked the gen12 schematic, and it seems to show that as well. The DAC, Tempo 92HD95B, is not within the pink dotted outline showing daughterboard components Framework-Laptop-13/Mainboard/Mainboard_Interfaces_Schematic_12th_Gen.pdf at main · FrameworkComputer/Framework-Laptop-13 · GitHub

Well that sucks.

That’s only the actual headphone jack from what I can tell, not the audio codec itself…

Although there are a few additional components on that board including what looks like transistors and a whole ribbon cable connecting it to the main board so I’m not sure if it’s entirely hopeless. Perhaps someone more knowledgeable on circuits can chime in; I don’t seem to see the part on the schematic.

If that’s an output buffer, maybe it’s even possible to fix the problem directly…

Unfortunately yeah turns out that is the case.

At least one of those components is the hall effect sensor for the lid close sensing. If I had to guess probably U12.

Maybe, not that knowledgeable in audio circuitry myself. And somehow the pinouts on the framework git disappeared.