IC: USB audio adapters

C

cranky

Skilled
Feedback: 27 / 0 / 0
Hola!

This is an IC for two versions of a USB stereo audio adapter open to Mumbai buyers (pickup after audition) or those can arrange pickup in Mumbai.

One is a regular version, which is essentially a bare PCB about 12cm by 8cm (cm, not inches) with all mounted components and flyout leads for output. It is small enough to be placed in a Pan Masala tin or Coke can - user can get creative with these choices. It can also fit quite neatly in a PC case (though not recommended), and we can include an option of wiring up the USB port internally. This runs off the USB power, and the sound quality is around the level of Emu 0404 or a Revo 5.1/7.1(quite a bit ahead of X-Fi). This should cost below Rs. 5000, in my estimation, and be a little cheaper in quantity. Will use respectable brand-name components on an imported double-sided PCB with full groundplane, and will mate well with most amplifiers and PC speakers. Note that since these run off the USB in your PC, they will be sold with a spot check, but no warranty. See below for why.

The second version is a deluxe version, which is a full-blown DAC. This runs off its own wallwart, comes cased in a nice Hammond enclosure, and adds post filter and buffer capabilities, plus uses hi-end audiophile grade components throughout. Black Gate caps, Metallised film caps and low-noise regulators. Voicing for user's equipment and taste may be done, at extra cost. Headphone amp (Cmoy type) is an add-on option. Sound quality should be as good as mid-fi DACs costing $700 plus. The selling price for these should be in the region of 12K, customisation excluded and final cost will depend on configuration. These have separately supplied and tightly regulated power, and will ship with limited one year warranty and free lifetime support (which basically means I will continue to answer questions and offer upgrades till I forget or die, whichever come first).

Let me explain how this is going to work.

If there are sufficient interests (5 of each is sufficient), I will order parts and boards at my own expense, and prototype the adapters. If I deem them fit to be released into the public space, I will offer them up in these two versions. The final costs may be lower (I have indicated absolute maximum cost, excluding any special feature requests). If they do not meet my expectations, I will announce the failure of the project by PM to interested members. I expect the project to start in Jan and end by early March if successful.

I will only have 5 of each type for sale in round 1. Round 2 will not start before May or June of next year.

USB and audio:

Note that the quality of any USB audio device totally depends on the USB chipset implementation of your motherboard and the quality of power from your power supply. Problems with either will result in degraded sound quality at the very least or unlistenable audio with clicks and dropouts at the worst. As a general guide, Intel's boards are very good in this respect, and in general Via chipsets are the worst (they tie with Sis for this honour though). When i hook up the prototype I will have some more concrete information about this, as I will test it on Intel (G965), Via and AMD690G chipsets, plus a bunch of laptop chipsets. Providing I don't blow them up, that is.

Feedback would be good, and delete the post if it violates any forum rules.
 
EVen though I don't need one now (already have a USB audio setup), cant resist but comment

Having used a M-Audio transit and audiophile, I can vouch for the quality of the audio output from USB DACs

The isolation from the main PC casing also ensures that the final output is electrically noise free
 
Superczar,

Except that the ground is dirty,. I still see RMAA results where USB power is badly contaminating test results. These clean up when the DAC uses its own power, or a very extensive cleaning up of the USB power. Pro devices do implement multiple filtering and maybe that's why you experience clean output with those.

Little 10 dollar dongles do not have any filtering in place. The version 1 mentioned above does have some amount of power supply filtering and regulation, but noise floor is about 10dB poorer than when an external supply is used. The difference is 85 dB versus 95 dB though, and 85dB is already a little better than Audigy2, and similar to an X-fi.

Thanks for your comments, always welcome.
 
Pro devices do implement multiple filtering and maybe that's why you
Click to expand...

The M-Audio audiophile does have a separate power brick while the transit does not

Even though I did not notice a perceptible SQ difference between the audiophile and transit, there is something else.

I did not measure the noise floor with an oscilloscope or SPL like i guess you did, but what I did notice was this:

At zero signal level (i.e. no sound playing on comp), if I increase the volume of the Amp to something like 3:00 PM or above, there is a very perceptible electrical noise on the amp in the case of the transit while the audiophile does not return any noise at all

Having said that, most people would not listen to music at levels so high
 
@greenhorn: Sorry, my bad.

The DAC used is a PCM2702. The datasheet is here: http://www.ti.com/lit/gpn/pcm2702 If you have problems caching the pdf, right-click and 'save target as...', and manually rename to pdf file.

The Power to the DAC is filtered using MAX1722 or equivalent three-terminal regulator. I'm hunting for suitable chips. Both versions have two filter stages, separate for analog and digital.

No opamp in Version 1, only passive filter at output.

Version 2 will use NE5532. Option for LM4562 or OPA2134. Since I've not prototyped it yet, will experiment with various config, but am pretty confident of the 5532, since it's used in about 80% of pro gear.

Both versions have SMD Dale resistors.

Version 2 uses Vishay 1/8 metal film resistors.

Version 1: Pana FC and FM caps and Elna SilmicII caps in critical bypass and coupling applications.

Version 2: BG NX Hi-Q output caps, TDK X7R bypass and BG NX Hi-Q for critical bypass and coupling, Panasonic FC and FM caps everywhere else.

There have been reports of a direct out sounding better than one with an opamp, I will investigate this. Practical results of the DAC are very good. There are some older measurements of some other implementations on the web, with very good performance. One such is here, linked from within the development thread for this line of DACs: RightMark Audio Analyzer test: comparison Sorry for the missing pics. The DAC performs excellently for running off bus power. It will work better with batteries (2 NimH 2300mAH batts will keep it running for 40 hours), and a brick is the best.

TechHead: As for Cmoy amps, it's more of an add-on. The reason I don't offer it is that there are many sources for fully built CMoys already, and i will not be able to match those in price by building them here. As you probably know India is very DIY unfriendly, and though I could build it, you could probably get it cheaper from abroad.

The second reason for the absence of headamps is that I don't listen to cans. I would not offer something I do not listen to myself - because then I can't judge what's good and what's bad. Having said that the service is available an a PM will help me work out something for you if you're interested.

@superczar: You don't need any test equipment. RMAA is free, and all you need is a loopback cable to test the noise floor, THD, IMD and a bunch of other tests. It's all done in the system.

Edit: If you want to DIY, the kits are available on glassjaraudio.com for 36 dollars plus shipping, excluding the case and output jacks. This will get you basically the version 1 in stock (untweaked by me) form, which is a pretty decent DAC. Non-Mumbai guys may want to look at this option.
 
Subscribed to your thread sangram, interested to see how this pans out... I'd surely pick one up once you've tested it.
 
thanks Rio.

Just a quick update: I've been researching this even more, and my suspicion that the output will totally depend on the power supply are verified.

Here is a comparison between a battery supply which is clean but weak versus USB which is dirty but strong. You can see how this shows up in the numbers, with the battery supply giving low noise floors but higher distortion.

RightMark Audio Analyzer test: comparison

And here's one more link, of the DAC running off a Toshiba Tablet PC, for both battery and AC power. In both cases the DAC is running off the USB bus power. Excellent results for such a low cost DAC, running off what looks like a very good laptop supply (don't expect similar results from all laptops).

RightMark Audio Analyzer test: comparison

Will post back once more people show interest.
 
Err just curious why that choice of converter. If you intend to make a non oversampling dac, why not the tried and tested Philips TDA1543? Not sure why but most BB based designs are all oversampling ones with PCM179x or PCM170x. I'd be really interested in knowing how this sounds once its done. If anyone in blore gets one, we can have an A/B session with my modded citypulse.

OT: Sangram where are you sourcing the blackgates from? I need a few to mod the output stage of dac.

Cheers and all the best for the project!
 
Thanks for the comments.

I'm not interested in NONOS type DAC for this particular project. The objective is simplicity and economy, so I'm looking for integrated receiver, converter and output stage. In my mind, USB DAC is a good solution for portable, laptop and entry-level desktop configurations.

My objectives were to make a compact, single chip solution that would sound excellent when powered off a dedicated supply, could run off AA battery pack or bus power if needed with a small sonic tradeoff.

I had considered the PCM2707 board from the Opus DAC I've mentioned earlier, but sonically the 2702 has much better specs, close to theoretical limit of 16-bit.

For the 1543 I would need a separate receiver, and the TDA runs best at 8 volts, so using bus power was impossible. It is no doubt a great DAC but it is not meant for this application. If I *had* to build a standalone, it would probably be triple stage with fully balanced dual DAC, maybe AD1865 or PCM1704. I plan these projects for end of next year maybe, and then we'll see if the 1543 fits in.

In any case, there's not been that much interest so I will maybe just make one of each type for myself, so costs for ordered units will go up (as I will not enjoy the benefits of combining shipping for multiple units). Also I was not offering them to people outside Mumbai for logistics reasons - I am not set up to handle this like a business. However there is a AlienDAC kit available, and that is cheap and easy to get as well.

I order my exotics from Partsconnexion or Percy audio. The regular stuff including FC and FM comes in from D-K, and I do buy the really heavy bits from Lammy. Boards come from verified sources, mostly individual kit suppliers. In the case of this project I was importing the cases as well, but probably not anymore.

OT: I would put film caps on the output of the DAC if I had to, or i would skip it and depend on the input of the amp to stop DC. I find industrial grade metallised caps actually have a wonderful place in audio, after some burn in they really come to life. There are some issues, but at less than 5 dollars a cap one can live with it.
 
The first prototype is alive.

I used the Alien for the boards and parts, before I start on my own PCBs.

I've built a version that's powered off the bus, and regulated and filtered to control noise.

The second version (I plan to finish building next week) will be a stripped down version with minimal filtering and regulation, and the third will be a full-on version with film caps or Blackgate, multiple regulated and noise-controlled supply, etc.

Initial impression is that the sound is much smoother and more 'velvet' in texture that I normally prefer (I like my sound a little edgy and close). Imaging is top-notch and the soundstage huge. It's a question of taste. It gives up very little to the CS4398 and the AKM4524 I can compare with, and since it's not on the PCI bus, there's very little electrical noise.

However it is very finicky about the quality of the PS. A generic PS has too much ripple, and the DAC lets you hear it. I'm testing soon with a VIP power supply, which is the baseline build for everyone here (and powers my 1212m), and will post back results.
 
The first prototype is alive.

I used the Alien for the boards and parts, before I start on my own PCBs.

I've built a version that's powered off the bus, and regulated and filtered to control noise.

The second version (I plan to finish building next week) will be a stripped down version with minimal filtering and regulation, and the third will be a full-on version with film caps or Blackgate, multiple regulated and noise-controlled supply, etc.

Initial impression is that the sound is much smoother and more 'velvet' in texture that I normally prefer (I like my sound a little edgy and close). Imaging is top-notch and the soundstage huge. It's a question of taste. It gives up very little to the CS4398 and the AKM4524 I can compare with, and since it's not on the PCI bus, there's very little electrical noise.

However it is very finicky about the quality of the PS. A generic PS has too much ripple, and the DAC lets you hear it. I'm testing soon with a VIP power supply, which is the baseline build for everyone here (and powers my 1212m), and will post back results.
 
OK we are live with the first demo-able prototype. PM me if you want to hear the soundcard. I had to fiddle with the thing (looks like it) to get it to a point where I was happy with it.

It humbles the bitstream DAC in the old SBLive! with LM4562, and is pretty much on par with the AKM4524 (slightest loss of top-end resolution, hardly noticeable with CD resolution material) in my Delta66. Timbral accuracy is great and the soundstage is huge. Output level is sufficient for deafening volumes from most speaker/amp combos. In short, it has none of the sound quality issues I feared. It is not as good as the 1212m in the midrange, but it still performs great for its size and cost.

Re-evaluating the costs and optimising the order I should be able to knock the price down to about 100 USD per unit after customs if I get 20 units at a time. This is significantly lower cost than the X-Fis which should have similar sound quality (don't have an X-fi, if someone volunteers we can do a head-to-head). We are looking at an external unit, though the prototype runs off an internal USB connector and is mounted on a PCI bracket inside a case.

The DAC is still bus-powered. I sensed little to no improvement by using external power using my MX5021, but on the main rig there was a slightly quieter background (audiophilia - 'Blackness'). Not enough to justify the cost of the upgrade, and anyway if your listening rig is that high-end you would have a dedicated source or DAC.

This is a good upgrade for:

1. People with only onboard sound and a decent pair of PC speakers (2300/MX5021), or an amp + bookshelf/floorstander combination.

2. People who want a good sound upgrade for a laptop.

3. People using onboard or a cheap soundcard for the front end of their cans.

4. People looking for a portable USB solution, no bigger than a pack of cards, that they can plug into any source around the house, and enjoy really good stereo sound from.

This is NOT a good upgrade for:

1. People with high-end listening setups. The few flaws of the DAC become more obvious as system resolution goes up. I find the cutoff is a pair of Jamos with my amps. On the Dynes or the Sony, the limited resolution is apparent and though the listening is enjoyable there is a bit of midrange resolution loss.

2. People who can't invest in a headphone amp and need source to directly drive cans.

3. People with regular PC speakers. I tested with ATP3, which has lower resolution than the DAC apparently. The differences between the DAC and the SB Live! are not detectable on the ATP3, even though it is an upgrade from the onboard audio (and you can tell the difference between the onboard and this one).

4. People looking to run gaming/movie surround setups. Theoretically you could pair up three of these DACs using ASIO4all and run a killer 5.1 setup, but it's quite a task in software. An X-fi is probably a better bet.

Known bugs:

1. Older (pre 2005) chipsets may cause USB dropouts or sync loss (detectable as loud white noise on the output). A restart definitely fixes it (internal), or unplug and re-plug the device (external) also works. nForce3Pro has flaky USB implementation, causing sync issues randomly. 690G, G965 and 680i tested flawlessly, they are the only 4 chipsets I own but are representative of 90% of new PCs. Intel chipsets of all vintage will be fine, Sis/Via will always be suspect in my book.

2. Windows XP upto SP2 does not remember volume setting if device is not connected before Windows starts up. If unplug and replug device volume is reset to 50%. SP# this is not an issue as the system recognises and remembers the device setting.

3. Power supply quality affects sound quality greatly. My 'Super Supply' (unbranded supply with best components and build I've seen for awhile) is the best, Antec somewhere just below, and the VIP below that. SQ differences are small, but definitely noticeable. With VIP the sound is a little duller, I assume due to more EMI on the lines. Ferrites on all supply lines have significantly corrected this, and is a big reason I did not venture into a stripped-down build. The SQ with the VIP supply is now acceptable, and as long as your supply does not have too much ripple on the 5V line you will be fine.

Specs for the technically inclined:

D/A: PCM 2702, USB DAC, 100dB S/N, -100dB THD+n, >90dB Dynamic range. RMAA tests to be carried out before the weekend and will be updated in thread.

Output: 1VRMS, 5K output impedance minimum

Caps: Elna RFS or SilmicII or Pana FC for output, Pana FM for powersupply, TDK low-distortion ceramics for all bypass.

Resistors: Susumu thin-film precision resistors .5% .1 watt throughout (!)

Separately regulated digital and analog supplies

Bus powered

Constructed on a double-sided silver-plated board

Using only highest quality silver solder

Housed in a Hammond 1455 black or silver enclosure (your choice), no bigger than a pack of cards or cigarettes (10, not 20s).

20 units is the lower cutoff for me. For lesser number price goes up (~10-15% I guess) as I don't get price breaks on the parts any more. PM me for more info, auditions or to express interest. I will process my onward orders/accept payments after sufficient interest.
 
Two questions I got from another member on my PM. Posting it here as it helps the discussion:

1) What PSU are you using? Whats the max current ratings on the rails?

2) Are you powering the adapter off the USB bus? If so, how? Have you found any audiophile quality switch mode boost PSU?

1) I have tested on three PSUs, an Antec TP480, a VIP/Powersafe 400 watt (silver) and an unbranded PSU which I would estimate at about 500 watts or so, comparing the transformer size and weight with the Antec. The latter performs the best and the VIP worst. I have no idea what the current rating of the generic PSU is, but I'm not sure it matters.

HardOCP and PCper have some nice tests where they also test PSU ripple on various rails at various load levels. It's important to choose PSU with low ripple to start with, and since music is a light-load activity, a PSU should not be stressed too much.

2) I am powering it off the USB bus, but the PCM2702 operates off that bus directly, does not need boost conversion. Actually the voltage is regulated down to 4.75 Volts, which is enough for the little guy. Boost conversion would require further regulation and possibly a noise shunt, both beyond the cost scope of the project.
 
I'll post some references. I only have a cellphone camera, pretty much useless in photographing a board with all SMD components on it. Everything will be a blurred mess.

Here's the case:

http://www.hammondmfg.com/1455B.jpg

This is kind of what it would look like if it had a volume control and a headphone amp (mine doesn't), this case is a little bit bigger than the one I'm using. Plus a mini-review!

» The Alien USB DAC - Entropic Memes

And a finished board (someone else's):

http://nuxx.net/gallery/d/54960-4/IMG_9039.jpg

The schematic is based off the Alien DAC (and built on the same boards), but I've changed a few things in the power supply area and the output configuration. Notably, I've replaced some of the ultra-low ESR caps with Pana FM, which seems better for the application in spite of worse specs. Also changed some cap values to improve the top-end response. I'm using 1206 X7R for some positions and have revised a few values to suit my tastes better, and the regulation circuitry is configured for a slightly higher voltage.
 
I'm assuming there's no interest, so abandoning the project. Too bad, it would have worked out as a nice entry level audiophile source for a lot of peeps PCs and laptops (and EEE type PCs).
 
I would have bought your version of the alien usb dac if you are building a couple as you needed. if you still consider , let me know.
 
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