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| tooki:
--- Quote from: Miyuki on December 08, 2021, 08:43:47 am ---And most phones have already that analog audio signal routed to the connector (either USB C or Lightning). It is just a matter of the shape of the plug on the headphones. --- End quote --- FWIW, I know that some Android phones do that, but on Apple devices the ports are purely digital, and the headphone adapters contain full DACs and ADCs. (Lightning doesn’t even have the option of analog audio out. It’s a strictly all-digital interface. Video output on Lightning is actually implemented as an h.264 stream, decoded in the HDMI “adapter” which actually contains an entire ARM SoC running a super-lightweight version of iOS just to decode the h.264 stream and run the HDMI port!) |
| tooki:
--- Quote from: NiHaoMike on December 08, 2021, 02:59:36 pm --- --- Quote from: james_s on December 08, 2021, 06:25:05 am ---There is no problem, you're making a mountain out of a mole hill. The PAM8403 for example puts out several watts running from a single supply and requires only a few tiny chip capacitors and there are numerous other options. I don't know what amp is inside my iPhone SE but it works perfectly both to drive headphones and feeding an amplifier and it works perfectly in countless other phones, music players and other devices made over the years. This "problem" has been solved years ago, we don't need to reinvent the wheel. --- End quote --- PAM8403 is differential output and will not work for driving headphones. There's no way around coupling capacitors or a negative supply rail with that antiquated design. I recall that back when the iPod was popular, the output capacitors were too small causing substantial waveform distortion at lower frequencies. Hence the emergence of portable headphone amplifiers, something that really shouldn't be needed for a device specifically designed for portable audio. --- End quote --- I’m skeptical of such claims. Perhaps with 600 ohm cans that needed tons of voltage, but test after test showed the iPod and iPhone DACs to be exceptionally good. Even the microscopic ones in the Lightning headphone adapters test really, really well. As for the PAM8403: you have to use a big resistor network to drive headphones with it, as shown here: https://www.edn.com/add-headphones-to-a-class-d-amplifier/ (It does work, I’ve done it in a pinch, though I’d just use a real headphone amp IC if given the choice.) But I have no idea what you mean about needing a negative supply rail: it doesn’t even support dual-rail operation, never mind require a negative rail! And caps are definitely not required, though they are recommended. |
| SilverSolder:
--- Quote from: NiHaoMike on December 08, 2021, 03:34:47 am ---[...] The problem comes down to either you'll have to have fairly large coupling caps to allow the use of a single voltage rail or you'll have to add a negative rail to a device that otherwise would not need one. [...] --- End quote --- Most modern designs would probably use a bridged pair of amps, to avoid this problem entirely. Silicon is cheap... Notice how smartphones have 2 or 3 cameras on the back, it is cheaper and more compact to put multiple sensors in there than it is to make the lenses move for different focal lengths! [edit] hmmm thinking about it, the common ground shared between Right and Left may be an issue with bridged amps. - Still, the problem seems to have been solved for decades! |
| james_s:
I was not suggesting using the PAM8403 for driving headphones, I was using it as an example of a small, simple and relatively powerful audio amplifier that runs on a single supply and doesn't require large capacitors. I'm quite sure there are numerous parts on the market more suitable for driving headphones, I'm just not familiar with anything specific. The big problem with headphone audio through USB-C is there is only one port, you cannot plug in headphones (or an external amp) while the phone is charging. It's all kind of silly anyway, I already have exactly what I want, a standard headphone jack on my phone, so just keep making phones that have that, problem solved. There is no good reason to get rid of it. |
| ogden:
--- Quote from: james_s on December 08, 2021, 08:10:13 pm ---The big problem with headphone audio through USB-C is there is only one port, you cannot plug in headphones (or an external amp) while the phone is charging. It's all kind of silly anyway, I already have exactly what I want, a standard headphone jack on my phone, so just keep making phones that have that, problem solved. There is no good reason to get rid of it. --- End quote --- Phones with audio jacks are still manufactured. Just get one. Stating things like "I like mechanical buttons" so every phone on the market shall have such, sounds laughable to say it politely. |
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