DAC/ADC with headphone amp

Basically the equivalent of a ES100 or Qudilex 5K. Balanced or single ended out and mic in with real hardware controls. Fine with those controls being via bluetooth on an app. I don’t really care about on pc controls as I am a Linux user. Ideally dual connect.

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I’m surprised this is the only post on higher end DAC. I’ve been looking around and there are lots of hobbyist projects like JEDAC - yet another take on a DIY high-end USB Audio DAC that have it covered on design but needs minimization. I’m also looking for an all in one USB DAC chip but seems like it’s a minimum of 3 element chain, USB->I2S->DAC->amplifier. Still kind of interesting to see if I can do that. I’ve been really pushing things on the home manufacturing (well home office for my company) and down to 0402 and ultra small nordic nrf52 modules, so seems with the right component choice a night high quality DAC setup shouldn’t be too hard. Anyone have other references for designs they like?

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This is an interesting idea, it would be nice to also include a 2.5mm balanced out option as well.

Right? Laptop with balanced out would make a very serious DJ platform or audiophile listening.

Would EMI be an issue though if it’s inside the metal frame of the laptop? As far as I know that’s the reason we moved away from internal sound cards to external DACs for desktop usage

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I wouldn’t say I’m an audiophile by any stretch. More of a random specs nerd. So I had to look up that people were using TRRS style for these balanced connections. So that’s new to me.

I never knew moving things outside had any motivation except for when things moved pci-e 99% of peoples needs were taken care of onboard and the only meaningful add-in cards left was video cards along with the rise of laptop is the desktop for mainstream people. With the exception of high end and professionals, gamers, and enthusiasts you needed to cater to the Apple crowd which was hyper-flip-floppy on does cards even exist (G5 compatibility agp re-pin, iMac “Pro” usb/thunderbolt, trash can usb/thunderbolt only, new Mac pro proprietary long connector) but apple had this tendancy to rewire internal ports breaking compatibility with things from the pc market (agp, their new two connector pci-e ideas) meaning the only way to address both markets was USB and external.

So if there is a motivation that EMI is an issue there are two easy ways dealing with this if it doesn’t need full isolation. Metal housing that is grounded or shield cans. However if you want to start going down the fully isolated then it unfortunately might size itself out of the little housing because need to optoisolate the USB and then transformers for the power stages.

I’m going to take some of this and mull it over a little.

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My main concern would be the fit for the 1/4" connector since it is longer than a 3.5 mm one.
Also, have electrical isolation and enough space for all the components. It might be better to have an external connector for the TRRS and others that could be connected if you wanted it would also allow for more flexibility.

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Grounding it might be difficult if it’s running without the wall charger, right? I’m no EE, just someone that recently started getting into audio.

I’ve just heard that external DACs are ideal because of the noise issue. Audiophiles will pay outrageous amounts of money for this sort of thing but you never see pcie sound cards worth anything anymore. It’s all USB adapters. Shoot, my crosshair VII has a really good onboard dac/amp, but it’s still limited by being on-board. Too much noise from the VRMs and whatnot.

Let me know what you think about it, a discreet dac would be pretty cool. Maybe check out what LG was doing with their phones and see if there’s anything there?

Yeah you are not gonna get 1/4 inch. But 4 pin 3.5 and balanced 2.5 should work if they aren’t too long. I mean most of the noise is from the power and you are gonna be stuck with that on direct attach USB device. LG’s are 4 ESS chips. 2 dac and two amp chips is my understanding. The 5K is really great because of how customizable the software stack. I mean I think the latest firmware had Harmon curves parametirc eq’s for many popular headphones.

Metal chassis of all laptops are grounded. Floating them could have some shocking effects (pun intended!). So that’s not an issue. It’s the expense of getting one machined actually, or laser sintered or what not. Not cheap for small runs. I don’t have one of these yet so I’m unsure if the current modules have metal or plastic housing with a silver coating.

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@Keith_Wakeham the cards shipped have a plastic frame with a metal outer extrusion glued on; same for the cover that slides off. Internally, the PCB is screwed into plastic. I agree, the USB-C port shields go to chassis ground, so what’s the worry?

A 3D printed expansion card enclosure wouldn’t leave much for a PCB. There’s probably enough room for a USB DAC if it doesn’t have to be flush with the sides, though.

But, in the spirit of the this laptop, I have an even worse idea!

In theory, the Realtek HDA codec chip has SPDIF out which would be used to provide an input signal to a DAC/HP amp. If you were to remove half of the lower left internal expansion card cover, the 3.5mm TRRS board, and the left speaker, there would be plenty of space for a high end DAC/HP amp, with the signal coming from the onboard audio (possibly 24-bit 192khz spdif?) and power from the USB-C port. And potentially, if the ribbon cable connector for the 3.5mm board were reconfigurable to pass SPDIF, then this would be a solderless modification (to the motherboard).

A lot of what-ifs, since the Realtek documentation is difficult to come by. Especially whether or not we can get SPDIF output without physically modifying the motherboard?

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Why would you use the onboard audio for a dac? You’re trying to send analog signal to a digital analog converter? At this point you’re just running an AMP only, right?

EDIT: I saw you say worse idea lmao. You got me good

I mean, the desktop motherboard I use is also grounded. Doesn’t stop EMI from getting into my audio. Like I said as well, your laptop isn’t super well grounded when it’s not hooked to your wall. It needs a connection to the ground and your skin (or jeans) isn’t a reliable one.

Interference will be an issue if it’s in the chassis more than likely. It won’t be too much for the average user, but the average user also doesn’t need a DAC either

He is saying that the onboard audio chip supports digital output via wired connection. He is wondering if you can tell the driver to output it to the existing wires. So onboard digital output to … but yeah I am not I think it makes sense.

what a madman. Yeah, you’re probably better off just using a type C port. Though they did basically say “an even worse idea!” so it’s probably more of an “in theory” than a “this is a good idea” kind of concept.

Funny to think about though

This is how I start most of my ideas. Modifying the original design like you mentioned certainly sounds possible. This would certainly be a more direct solution, though my gut feel is it would be a little too much for most people. Though maybe not for the framework early adopters who then fit into the niche of wanting this.

On my quests to figure out the USB to I2S (or SPDIF) it seems that there are some projects (and reference code) for using STM32F4 chips and they support up to 24/196. That would simplify the whole thing, and if a bootloader could be made compatible that could provide a really nice avenue for some some open hardware and while plugged in could do firmware updates if there is further development and fixes.

STM32F4 → PCM1794 → amplifier (fully differential using 2.5mm/3.5? TRRS and a normal one for normies like me?). I kind of like this solution. It feels in the spirt of these modules and accessible by opensource programmers. Now I just need to break my addiction to commercial software packages and try and do this in kicad for accessibility.

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I think I thwarted myself. While my company can’t get basically any ST MEM’s and no ship dates in sight and last restock Digikey only allowed sales of 30pcs (also, similar problem with Nordic nrf chips, limits of 50), I hadn’t realized the stocking shortage has basically extended to almost all of ST’s Arm cortex based chips. Can still get dev kits but based ST doesn’t give the disti’s ship dates lately and likely couldn’t build one around a STM32F4xx until mid 2022 according to CEO projections unless I was placing orders for reels. Sad Panda. Might keep looking for another option. Parts shortages will really hurt ideas for DIY sadly.

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I actually did a bit of listening to the onboard vs a much higher end dac with the same amp and cans and it was quite close. I would say the onboard is good enough for audio out.

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Ah with sensitive IEM there is a pretty loud noise floor compared to my Qudelix 5K. So that is funny. Maybe something slightly harder to drive is actually better for the on board amp as it just isn’t that quite.

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