USB DAC - Page 1
Forum section: electronics / projects

author: gnif
author_rank: Unknown
timestamp: September 21, 2017, 04:23:59 am
content: Hi Everyone,I am looking for some imput on an affordable decent quality USB DAC that implements a standard interface that would be well supported under both Windows and Linux. I intend to drive my own analogue preamp from it, so a simple line out device would suit. I would also like it to have the ability to handle a line input for recording. Note that I am NOT looking for audiophoolery devices, just a basic interface that works well for the price with decent SNR.Suggestions very welcome

author: ruairi
author_rank: Frequent Contributor
timestamp: September 21, 2017, 04:35:46 am
content: Check out the ODAC -https://www.jdslabs.com/products/39/odac-objectivedac/I haven't actually heard one but reviews are very good and the design is solid. I may actually be ordering one this week so if you are not in a rush I will let you know how it fares.It has quite an interesting backstory and development that makes for some good educational reading -http://nwavguy.blogspot.com

author: gnif
author_rank: Unknown
timestamp: September 21, 2017, 04:52:53 am
content: Quote from: ruairi on September 21, 2017, 04:35:46 amI am in no rush, I will await your feedback on this, the price is in my budget also.Quote from: blueskull on September 21, 2017, 04:45:58 amThanks but the cost of these devices is prohibative, I also do not require or want any of the pre-amp or conditioning they have as I am already running through my own diy HiFi. I also want a device that 'just works', I swap between operating systems continually for work and need the device to just work.I have moved all my audio conditioning external and in the analogue domain so that when I switch operating systems my audio experience is the same without having to mess around with any software EQ, etc.

author: stmdude
author_rank: Frequent Contributor
timestamp: September 21, 2017, 05:05:03 am
content: I've used the TI PCM2705C for a USB DAC build. It's specs are nothing to write home about, but it's a massive upgrade from any integrated soundcard in your laptop or desktop.I've used it successfully in Windows 7/10, Linux and OSX. It also works out-of-the-box with OpenELEC to get decent sound out of a RaspberryPI.Now, the 2705C doesn't have line-in, but the 2704 (and some others) do. Haven't tried that, but I don't see why it wouldn't work fine.Typical specs:16bit, various samplerates up to 48KHzTHD = 0.025% (When bus-powered, selfpowered is 0.006%)SNR = 98dBYep, definitely not audiophoolery, but still gives very nice HQ audio for its price.

author: gnif
author_rank: Unknown
timestamp: September 21, 2017, 05:28:26 am
content: Quote from: stmdude on September 21, 2017, 05:05:03 amThanks, yes, I had already moved to a better card some time ago (Asus Xonar DX) but I am sick of getting hiqh pitch inteference from the 4x HDMI interfaces under certain conditions. I know I can run audio transformers to isolate everything but I figure if I just move to USB I won't have to mess around so much.

author: stmdude
author_rank: Frequent Contributor
timestamp: September 21, 2017, 05:39:27 am
content: Quote from: gnif on September 21, 2017, 05:28:26 amAh, I see where you're coming from then.Yep, internal soundcards (even the after-market ones) are very hit-and-miss due to the amount of interference inside the computer case.I've also got an Asus Xonar U7 which might fit your bill. I've had it working in Linux, but I'm not certain if I ran it in USB 2.0 mode or 1.1 mode. (The card/box has a switch underneath it to switch between audio class 1.1 and 2.0, which is a neat feature)The jog-wheel is a regular USB HID device, and work fine in Linux as well.

author: ruairi
author_rank: Frequent Contributor
timestamp: September 21, 2017, 06:54:55 am
content: Quote from: blueskull on September 21, 2017, 04:45:58 amIn the interests of full disclosure I should say that I do some repair work for a competitor of Apogee but I would disagree with your recommendation. I own a lot of DACs from Prism Sound, Cranesong, Benchmark, Avid and a bunch more. Having spent way too much time comparing DACs in proper level matched comparisons in acoustically treated mastering rooms Apogee would be near the bottom of my list.I've never heard ESI.

author: ruairi
author_rank: Frequent Contributor
timestamp: September 21, 2017, 08:40:12 am
content: Quote from: blueskull on September 21, 2017, 07:52:31 amMy comments about the Apogee were all about sound, they just don't sound very good in the main. Apogee have long been excellent at marketing. I've heard them many times and have recorded with various models too.I've seen mention of the ESI cards before, thanks for the info.

author: grifftech
author_rank: Frequent Contributor
timestamp: September 21, 2017, 05:58:19 pm
content: https://www.amazon.com/s/ref=nb_sb_ss_i_9_6/134-2064435-5277152?url=search-alias%3Daps&field-keywords=usb+headphone+jack&sprefix=usb+he%2Caps%2C155&crid=2LM2WTP01D3P2not the mp3 player cable

author: gnif
author_rank: Unknown
timestamp: September 22, 2017, 12:17:29 am
content: Quote from: grifftech on September 21, 2017, 05:58:19 pmThanks, I know of these devices, I am looking for something of decent quality with good SNR, which these do not have.

author: BrianHG
author_rank: Super Contributor
timestamp: September 22, 2017, 12:41:38 am
content: If you do not want PC interference, why not use optical audio or SPDIF out of your motherboard and use an off the shelf DAC interface. These 2 interfaces separate from your PC's power supply completely... (Just pass the SPDIF through any cheap data link transformer...) Seeing how your on this site, and today, 10 PCBs for 5$, you can build a top notch DAC to your exact spec which will never have any power connection to your PC unlike USB dacs which will still share a ground and be powered from the PC.

author: gnif
author_rank: Unknown
timestamp: September 22, 2017, 12:51:29 am
content: Quote from: BrianHG on September 22, 2017, 12:41:38 amI have considered this but have decided not to for several reasons:1) It wont 'just work', espesially under some configurations I run such as Linux + ALSA. I know first hand how terrible ALSA is with dealing with optical links (I wrote the audio code in Kodi that does all that mess).2) I already have several USB isolators for keeping my DSO from grounding out through it, might as well use one for this3) I'd like to plug it into my laptop from time to time which has no optical or even coaxial support.

author: BrianHG
author_rank: Super Contributor
timestamp: September 22, 2017, 01:21:23 am
content: Quote from: gnif on September 22, 2017, 12:51:29 amWarning, for Audio Class 2.0, your will need high speed USB support, otherwise, you'll be stuck at 48KHz, 16bit stereo...Are you looking for an IC like this?https://www.cmedia.com.tw/products/USB20_HIGH_SPEED/CM6632Ahttps://www.cmedia.com.tw/products/USB20_HIGH_SPEED/CM6631AAt 7$, plus you can interface it with an I2S DACs and ADC of your choice, you will have what you want.(I personally would just insert an opto data isolator on the I2S lines, something like a SI8065AA an forego an external usb isolator, power the analog side from an AC output transformer making a nice isolated dual supply...)Damn, now I'm tempted to build one... I just need to find the right DAC & I would like the option of +4dbu or even +6db output.

author: gnif
author_rank: Unknown
timestamp: September 22, 2017, 01:39:48 am
content: Quote from: BrianHG on September 22, 2017, 01:21:23 amHrmm, that blows that idea out of the waterQuote from: BrianHG on September 22, 2017, 01:21:23 amI would be but that is beyond my current EE abilities, or time that I have available to learn to build it. That has capture too which would be ideal.Quote from: BrianHG on September 22, 2017, 01:21:23 amMake two

author: Buriedcode
author_rank: Super Contributor
timestamp: September 22, 2017, 02:27:33 am
content: Most of the cheap USB soundcard dongles use the CM108 from C-media. Surprisingly OK quality. On board PLL ADC's/DAC's, on parr with the ancient PCM2704, but for a fraction of the price.Almost all USB DAC's will be asynchronous, and be limited to 16-bit @48kHz. The newer USB audio 2.0 spec can have higher bit depth and 96kHz sample rate, but its overkill for playback. Whilst synchronous transport sorts out the any jitter, I don't think the difference is particularly noticeable.As you're after >16-bit @48kHz I can only assume the application isn't audio listening, so what is it for?

author: gnif
author_rank: Unknown
timestamp: September 22, 2017, 02:29:09 am
content: Quote from: Buriedcode on September 22, 2017, 02:27:33 amIt is for audio listening, but I also mess around with analogue audio and sometimes require the higher bitdepth and sample rate for SNR and THD measurements. Basically I use the PC as a poor mans signal generator, all hobby level stuff so good enough for it.

author: BrianHG
author_rank: Super Contributor
timestamp: September 22, 2017, 02:36:20 am
content: I'm willing to design it here, open source & proofed on EEVblog (in a new dedicated thread). However, I will be designing the schematic and PCB in Protel 99se. I know it's old, but I legitimately own it, know how to use it's in and outs, and, I'll provide all source files, gerbers, and documentation... Everything will be 100% manual routed...The PCB will have the USB interface with optional isolated DC-DC converter for the dac and analog section, or, an AC input with regulators. It will be the choice of which components you stuff. The I2S Data lines will be opto-isolatedThere will be line level output on RCA, with maybe an optional balanced output, or, 8 channels out instead. I don't know which yet.Stereo input will be there as well.You will be able to set a fixed optional +Xdb gain resistor on the output as the output driver amp will have a +/-12v supply with the headroom.If there are any additional takers, let me know now as it will help me decide whether to go or not....If there are any special additional considerations, let me know as well.

author: gnif
author_rank: Unknown
timestamp: September 22, 2017, 02:40:28 am
content: Quote from: BrianHG on September 22, 2017, 02:36:20 amSounds perfect! Link the thread here if you start one!

author: WZOLL
author_rank: Regular Contributor
timestamp: September 22, 2017, 03:05:32 am
content: I used to have one of those c media sound cards when the headphone jack broke on my laptop. The SNR and quality was dreadful. I bought one of these as a replacementhttps://www.amazon.com/gp/product/B000KW2YEI/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1. For 48 kHz, 16 bit converters and fantastic SNR and audio quality, it's decent value IMO.

author: BrianHG
author_rank: Super Contributor
timestamp: September 22, 2017, 03:21:57 am
content: To give you an idea of the digital side, take a look at this PCB using the CM6631A IC:http://www.ebay.com/itm/2017-new--IIS-digital-interface-compatible-with-Italy-Amanero-192K-32BIT-/272551321329?hash=item3f75531ef1:g:MTQAAOSwblZZHaR2

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 22, 2017, 03:26:29 am
content: Maybe track down a reputable source for quality USB-C DACs or the chips used in them? I know at least the ones LeEco uses (appears to be SaviAudio from the USB IDs) are very good.Quote from: gnif on September 22, 2017, 12:51:29 amI have never had any issue with PCM stereo over S/PDIF, at least not on the software side. What is problematic is surround over S/PDIF, in that there are multiple standards.

author: BrianHG
author_rank: Super Contributor
timestamp: September 22, 2017, 11:14:57 am
content: Before I begin, I would like to test out the CM6631A for compatibility, however, I can only test for windows 7. Is anyone else interested enough to pick one of these CM6631A boards?https://www.aliexpress.com/item/2017-NEW-CM6631A-USB-Digital-interface-32-24Bit-192k-USB-To-I2S-SPDIF-coaxial-Output-With/32822375930.html?spm=2114.search0104.3.50.l0QSr5&ws_ab_test=searchweb0_0,searchweb201602_4_10152_10065_10151_10130_10068_10344_10342_10343_10340_10341_10139_5550020_10307_10137_10060_10155_10154_10056_10055_10054_5470020_10059_10532_100031_10099_5460020_10338_10339_10103_10102_440_10052_10053_10107_10050_10142_10051_10325_5380020_10326_10084_10083_5370020_10080_10082_10081_10178_10110_10111_10112_10113_10114_143_10312_10313_10314_10078_10079_10073,searchweb201603_30,ppcSwitch_5&btsid=9554feed-9509-43a4-8ed3-db27711f35c6&algo_expid=d6ef9ad1-f2c3-4b7b-ad7a-bcc648ed3886-6&algo_pvid=d6ef9ad1-f2c3-4b7b-ad7a-bcc648ed3886I know it has a cheap 30$ DAC for the analog section, but, it's basically the CM6631A with an I2S output port and SPDIF coax out for the digital side and it should be adequate for OS compatibility testing & checking for any audio artifacts due to poor USB audio buffering.If anyone else is interested in testing for other OS since I just have Windows 7 Pro, let me know...

author: Buriedcode
author_rank: Super Contributor
timestamp: September 23, 2017, 04:39:55 pm
content: Quote from: Buriedcode on September 22, 2017, 02:27:33 amI should correct this to isosynchronousAsynchronous is where the DAC runs its own clock and provides feedback to the host rather than constantly adjusting to the hosts clock using a PLL (adds a bit of jitter).I can't say I hear the difference between the two, but it isgenerallyaccepted that it improves performance since the sample clock isn't dithering.If you're after designing your own, there is a PIC32 app note for USB audio and I2S, and a slight modification of the example project of 'USB speaker' allows for async operation. I believe the NV1 used this:http://www.diyaudio.com/forums/digital-line-level/244123-usb-audio-pic32-processor-pcm1796.htmlWhilst microchips framework is a bit of a nightmare, I vaguely remember having this up and running in an afternoon on a PIC24. Never made measurements though (just didn't hear any artifacts).

author: gnif
author_rank: Unknown
timestamp: October 02, 2017, 09:06:55 am
content: Quote from: BrianHG on September 22, 2017, 11:14:57 amI am in, sorry about the delayed reply, I have been away the last week on break. I can test underDebian 6, 7, 8, 9CentOS 6, 7Windows 7RaspianArmbianEdit:Unfortunately AilExpress doesn't like shipping to my area, it doesn't even list it as an option. If you can provide a comparable device on eBay I will go that way instead.