Headphones DAC - Page 1
Forum section: electronics / projects

author: Kasper
author_rank: Frequent Contributor
timestamp: December 11, 2019, 07:31:54 am
content: Hello,I am looking for a high quality DAC for headphones. I am hoping to find a DAC that can drive headphones directly without needing an additional IC headphone amp but I am wondering:Is it worthwhile to look for a DAC that can drive headphones or should I look for separate ICs, 1 DAC and 1 or 2 headphones amp(s)?Do you know of any good parts or places for me to search for parts or good places to learn more about this stuff?Having trouble searching for this because the DAC category doesn't list power or min load and the amp category doesn't list DAC specs.Found a few parts but the few DAC specs they list aren't really great sounding.TI: TLV320DAC3203Maxim: MAX9850ETI+TAnalog Devices: SSM2518CPZ-R7Tried googling best DAC for headphones and things like that but just get a bunch of complete products not ICs.Requirements:No DC blocking capacitors requiredPower efficientAnalog outputs: 2High quality audioGoals:Resolution: 32 bitSNR > 100dBSampling rate > 300 kHzPackage: small, preferably not BGAOutput power high enough for headphonesLoads (headphones): down to 4 ohmsBonus:Something that can drive a portable speaker like those common bluetooth speakers.I understand my goal specs might be overkill and I hope we can save that debate for elsewhere.

author: jhpadjustable
author_rank: Frequent Contributor
timestamp: December 11, 2019, 08:02:20 am
content: Digi-Key or Mouser might keep slightly more comprehensive specs in their online catalogs.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 11, 2019, 09:00:14 am
content: It absolutely makes sense to separate the DAC and driver / amplifier part in two chips. This keeps the heat (though not that much) away from the DAC. Also DAC and amplifier tend to prefer different chip processes.Some of the other goals don't make that much sense: AFAIK the highers data rate audio format is 24 Bit and 192 kSPS. Even that is way better than usual SNR and BW of the ears (even for many bats). 100 dB SNR calls for a 16 Bit DAC (in theory and with the high sampling rate even 14 bit could do).

author: magic
author_rank: Super Contributor
timestamp: December 11, 2019, 12:42:44 pm
content: PCM2704/6, VT1620A, TP6911, ...Such chips exist. They are neither particularly spectacular DACs nor particularly spectacular power amps. Many have outputs referenced to midsupply rather than ground.High end DACs may not even have voltage outputs but current outputs designed for an external I/V stage. Not that it prevents anyone from doing otherwise, and there are people who swear by the sound of vintage R2R DACs with "passive I/V" (aka a load resistor) or perhaps even driving headphones directly but that's a peculiar fetish which may not be appreciated by everyone. If a DAC has voltage output, it is likely to be weak-ass plus see the post above. Even opamps have problems with output transistors heating up the input stage.

author: Gyro
author_rank: Super Contributor
timestamp: December 11, 2019, 01:05:09 pm
content: Quote from: Kasper on December 11, 2019, 07:31:54 amHard to do that when your requirements (at least for any direct drive DAC) make your goal impossible.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 11, 2019, 01:25:11 pm
content: I have to agree with 24 bit/192kHz being plenty if the application is standard audio. (There is potential use for higher sample rates with speakers for software defined sonar for gaming.) With that in mind, I think the SaviAudio chip that LeEco uses would be as close as you can get as far as combined DAC/amp chips go. It would most certainly be a tiny BGA and I don't have a clue where to get just a few.You'll be better off with a DAC+opamps design.https://github.com/NiHaoMike/OpenDAC-HD/blob/master/OpenDAC_sch_ana.png

author: Kasper
author_rank: Frequent Contributor
timestamp: December 11, 2019, 04:42:34 pm
content: Thanks for the replies everyone. Great clear explainations. I'll quit looking for DAC with amp and look for separate DAC and amp.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 11, 2019, 04:52:34 pm
content: I don't think you'll find anything fitting your requirements in a single chip. Anyway, properly driving headphones with impedances down to 4 ohm will require something beefy; a TLV320DAC3203 or similar won't cut it. You may have some better luck with some class-D amplifiers with an integrated DAC (TI has a few), but they will probably not meet your requirements in terms of SNR.But if you absolutely need to fulfill your end goal... (I'm not gonna discuss the relevance of your requirements, it's your call, but frankly, if "all" you need is a SNR > 100dB, you don't need 32-bit.)If you still want a 32-bit DAC, your choice will be pretty limited and you'll have absolutely NO choice but using a separate DAC and amp section. The additional sample rate > 300kHz spec is another hurdle. For instance, there's the PCM1795, a 32-bit, but 200kHz max DAC. Then there's the "top of the line" AK4499EQ from AKM (supports up to 768kHz). About $83 at Digikey. Edit: just noticed it had 4 channels; you could go for the AK4497EQ instead, more "affordable" at $50, but interestingly, the 4-channel version has better specs.For the output stage, Your additional requirement of no DC series capacitor is yet another hurdle. I actually designed two amps with no output caps (one headphones amp, one 70W RMS power amp), and both with symmetric power supplies. This requires careful design and ideally additional monitoring circuitry to avoid any speaker damage in case something goes wrong...

author: magic
author_rank: Super Contributor
timestamp: December 11, 2019, 04:55:07 pm
content: Quote from: Gyro on December 11, 2019, 01:05:09 pmWell, if you are a purist and don't quite trust those "amplifiers", youcouldprobably get decent performance and load driving capability by paralleling enough of voltage output DACsAlternatively, somebody could make a huge die DAC/amp on TO-264 so never say never.

author: Gyro
author_rank: Super Contributor
timestamp: December 11, 2019, 05:31:44 pm
content: Quote from: SiliconWizard on December 11, 2019, 04:52:34 pmWith a 4R load requirement, something like a pair of LM3886s might be a good match. Easy to implement (as long as you include the 'optional' passives), and it has that 'Gainclone' cachet.

author: magic
author_rank: Super Contributor
timestamp: December 11, 2019, 06:23:15 pm
content: Are there actually any headphones with 4Ω impedance?I don't think they get below 16Ω, except for some recently introduced crazy ribbon stuff which is less than 1Ω.

author: Kasper
author_rank: Frequent Contributor
timestamp: December 11, 2019, 06:34:41 pm
content: Quote from: magic on December 11, 2019, 06:23:15 pmI don't know, I'm not really familiar with this area, just want to make it flexible enough to handle whatever is out there.Search on digikey for waterproof speakers between 30mm and 50mm shows 4ohm and 8ohm is most common but most of them are rated for about 2W which I think makes them more suited for portable speakers, not headphones.Ideally my product can drive portable speakers or headphones but headphones is the main focus so if the extra power required for portable speakers causes too much extra size or cost then I'll scrap it or consider making a 2nd model for that.Any idea where I go to find good waterproof speakers for headphones?

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 11, 2019, 06:38:27 pm
content: Quote from: magic on December 11, 2019, 06:23:15 pmYou can find older headphones with 8 or 4ohm impedance. I think they were more common in the 60s/70s? Maybe some ultra-audio("phile") stuff? Even the Grado headphones, which are expensive shit (well regarded but eek.), are typically 32ohm. I personally have AKG headphones which are good without a bullshit price, and they are 32ohm IIRC. (Most of AKG line is between 16ohm and 60ohm+).That said, even at 16 or 32ohm, good headphones (like the AKG) need a somewhat "beefy" amplifier - they are usually not as efficient as low-end headphones (in terms of dB SPL/W), and kinda sound like shit with low volume when plugged into those small crap integrated headphones amps.

author: Kasper
author_rank: Frequent Contributor
timestamp: December 11, 2019, 06:39:24 pm
content: Ok, let's talk specs.1 - What specs do I need to make high quality headphone audio?2 - What specs do I need to get sales?In the market I've been watching, products with over the top specs get way more sales than products with good prices.I don't want to spend $50/DAC and I don't want to hose the audiophiles. I just want to fill that void between great and good. Specs to appease audiophiles without going too far overboard and making it needlessly expensive.I think $10/DAC at qty 100 should get specs that rival the audiophile grade over-priced stuff. Does that sound reasonable?

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 11, 2019, 06:50:28 pm
content: Quote from: Kasper on December 11, 2019, 06:39:24 pmAs far as DACs go, any good 24-bit DAC is all you need here. A lot of choice really for a few $ each. 32-bit would really be overkill here IMO and would make your product almost look close to "audiophool" stuff. The PCM1794A for instance is a "classic", and very good ($9.9 per 100 at Digikey). Supporting sample rates over 192kHz is IMO unncessary. No audio material is routinely available with higher than this anyway, and if you look at the figures carefully, you'll find out that the DACs supporting higher than 192kHz will have degraded performance for the higher rates. Not much benefit in practice.The "critical" part will be the power amplifier stage IMO. Whereas getting better than 100dB (or even 105dB) SNR is definitely not too hard with a decent DAC, proper supply and proper PCB layout, getting this level of SNR for the whole chain up to the headphones will be much more difficult.

author: Gyro
author_rank: Super Contributor
timestamp: December 11, 2019, 06:57:59 pm
content: Quote from: Kasper on December 11, 2019, 06:39:24 pmI thought you were looking at making an 'as-simple-as-possible' one-off for yourself!It sounds as if rather more market research is needed before you start picking components.

author: Bud
author_rank: Super Contributor
timestamp: December 11, 2019, 07:00:31 pm
content: What is your audio source you plan to connect the DAC to? USB? Optical? Arduino?

author: Kasper
author_rank: Frequent Contributor
timestamp: December 11, 2019, 10:59:26 pm
content: Quote from: SiliconWizard on December 11, 2019, 06:50:28 pm*just kidding* who cares about layout, as long as I can put 32-bit in the ad */just kidding* aside from spending a few extra bucks and potentially looking like audiophool, are there other downsides to going with 32-bit?Can you recommend any good resources for learning more about layout practices for good SNR?I've been learning about EMC lately and seeing conflicting advice from EMC people saying never separate ground planes even when datasheets recommend separating analog and digital. I do not have funds for multiple tries at EMC testing so I aim to make something that has good SNR and good EMC compliance.

author: Kasper
author_rank: Frequent Contributor
timestamp: December 11, 2019, 11:01:11 pm
content: Quote from: Gyro on December 11, 2019, 06:57:59 pmI'll be my first customer but yes I would like to sell them too. All my research has shown big fancy numbers and new technologies get many more sales than good prices.

author: Kasper
author_rank: Frequent Contributor
timestamp: December 11, 2019, 11:12:58 pm
content: Quote from: Bud on December 11, 2019, 07:00:31 pmI hope to make it as flexible as possible. May turn into multiple products eventually and don't want to have to redo it just to add something later.I once worked somewhere where we were tasked with designed a doorbell camera. At first the boss wanted a cheap low res camera, then every time it was half finished he decided he wanted higher quality and our camera guy's face turned red. They went through a few engineers that year. Last I heard they gave up because it took too long.I don't want to start with something super optimized and barely good enough and kick myself later when I have to redo it just to up the specs a little bit. I'd rather start with overkill and be well set for whatever other ideas I have.This is one of several side projects I do after hours. Progress is very slow. By the time it's finished, 64-bit might be the standard and 32-bit might be considered old garbage.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 12, 2019, 03:30:08 am
content: Quote from: Kasper on December 11, 2019, 10:59:26 pmWell, aside from probably not being useful, one of the downsides, if you take a look at datasheets, is that affordable 32-bit DACs (eg: PCM1795) have actually worse specs than the good 24-bit ones (eg: PCM1794A) for similar prices. And as I mentioned, better 32-bit DACs are pretty expensive.Another point related to what Bud asked you: what will be the typical sources? Most common input sources do not support 32-bit anyway, so you'd be using a 32-bit DAC with only 24-bit (at best) samples, with again usually worse specs. What would be the gain?As to be future-proof, I dunno. No one can predict the future, but I kind of doubt 32-bit is going to be standard any time soon. One reason is that we're getting very close to what's reasonable on a physical level here when it comes to audio. You'll probably have ample time to make a rev. 2 of your device if you ever see signs that it's going to happen.One reason to use a 32-bit DAC would be to avoid having to reduce quantization if your input source is natively 32-bit - because no matter how good the reduction is done (with proper dithering), it's never going to be as good as the original. But as I said, I don't know of any source currently that is *natively* 32-bit, at least from the standard ones.Anyway as I said, if you do things really really right, you may be able to get something like 110/120dB SNR with a *good* 24-bit DAC, but only up to its output stage. The power amp stage - that's another story, and something you should definitely work on to get any benefit from using a DAC with better than 100dB SNR (or even 90dB...!)Quote from: Kasper on December 11, 2019, 10:59:26 pmHmm not really, but I'm sure some other people here can point you to some books or something.Quote from: Kasper on December 11, 2019, 10:59:26 pmAh yeah. What I can tell you is that most often the better way is to simply use a single solid ground plane and NOT split ground planes. The latter should be used sparingly, only for very specific cases, rarely when there is high speed digital stuff involved (which is the case with DACs). Just don't do it here. But you should definitely route your signals so there is minimal crosstalk between the analog and digital ones.

author: hamster_nz
author_rank: Super Contributor
timestamp: December 12, 2019, 03:54:00 am
content: I'm quite interested in hearing about what you do. I've been playing around with line-level 24-bit I2S ADCs and DACs lately, but without any serious aims in mind.Sadly I lack the T+M gear needed to do most useful measurements of the performance difference that PCB layout and component selection offer...

author: magic
author_rank: Super Contributor
timestamp: December 12, 2019, 08:52:20 am
content: I don't want to be a demotivational ass, or maybe don't want you to know that I am an ass, or whatever, but...The DAC/amp market is a thing, and there is plenty of stuff already there. From single-chip junk I mentioned before, which starts at $1 apiece, through all the FiiOs, Dragonflies and Schiits, up to the ludicrously "high end" with 768kHz sampling at 32bits or special snowflake DACs made of discrete resistors matched by nude virgins or FPGAs running custom delta-sigma modulators.There is surely no hope for one chip solution, because the Chinese would already be selling reference boards of that chip on Ali and you would stand no chance against them. And for many chip solution, you really need to go to places like head-fi or ASR and get some idea of what's out there and come up with good reasons why anyone would buy yet another DAC/amp instead of something already out there. Some of which is "cheap enough I might buy it for shit and giggles", some of which is "good enough for audio per NwAvGuy", some of which is "higher spec than the competition" - all is covered.editMaybe you should just figure out a way of mounting the Khadas Tone Board inside the JDS Atom, or whatever are the latest cheap and well-measuring toys that guys over at ASR are going crazy aboutOh, and I forgot. Make sure you have an idea how to power that gadget (USB 2.0 gives you only 2.5W, not really enough for 10WPC class A into 4Ω) and I hope you know what jitter is because you will be asked about it whether you know or not.

author: Kasper
author_rank: Frequent Contributor
timestamp: December 12, 2019, 05:54:21 pm
content: SiliconWizard:Thank you for the info. I will keep it in mind as I continue my search.hamster_nz:that is a nice looking board, thank you for sharing. I too lack T+M gear, aside from the EEVBLOG fan package: ds1054z and a 121GW DMM. I think I'll try to send a beta unit to someone with good gear to write up specs for me.magic:I appreciate the feedback. If you really wanna be an ass you should use fallacies instead of detailsAll I see there is a well laid out descripion of warnings I should consider and directions to where I can find more info and I appreciate all of that. I understand the audio market has a ton of competition (and consumers). Normally I avoid that type of stuff and focus on unique products because I can't compete with big players except for my very low cost of R&D. But in this case I think I have a unique idea. I tried buying the product I want but could not find it so now I am trying to fill this void. I understand if it does well I'll probably get copied and squashed by much bigger players but that seems to be the case with everything and maybe less so in audio. Really not sure about this part but it seems there is some appreciation for high end products from small companies in audio.

author: David Hess
author_rank: Super Contributor
timestamp: December 13, 2019, 03:23:36 am
content: I would use separate ICs for reasons given earlier and because it gives more flexibility to produce a good circuit layout. And there are many good audio operational amplifiers suitable for driving headphones directly now if you want to keep things simple.

author: floobydust
author_rank: Super Contributor
timestamp: December 13, 2019, 03:35:02 am
content: I use 600 ohm headphones and two op-amps - one for the reconstruction filter and an second as a line driver.I had a chinese Lehmann headphone amplifier clone, and it was total junk. It sounded annoyingly distorted and I found the usual- fake op-amps, and reject transistors, bad PCB layout etc. I tried to fix it but the distortion was never as low as direct drive which is what I use.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 13, 2019, 04:13:46 am
content: Quote from: SiliconWizard on December 11, 2019, 06:50:28 pmGo for PCM1792A instead, almost the same except it has a built in PGA so you won't need an external one to set the volume.