Audient iD22 teardown PCM4220+1798

Despite having hoped to nab an Audient interface for some time now, only quite recently did i manage to get my hands on one. Since i'm a cynical... [ahem] person, after having heard several notable(?) audio engineering channels over on Youtube ranting and raving about these, and the "Audient console preamps", and the "discrete JFET DI" and whatnot, my curiosity was indeed itching to see if and how the reality lives up to all the hype and marketing.

 



This one, according to the seller, basically had the whole of the analog side of things dead. The unit still connected to the computer, got recognized by its control software, and the digital ins & outs work, but no activity on the analog ins & outs. The listing also contained a couple of internal photos, and mentioned that a power chip used to have a heatsink glued on top of it, that had fallen off. Judging by the groups of components around that and the associated transformer, that looked to be in charge of precisely the analog rails. But let's not get ahead of ourselves, one thing at a time.

A reasonable complement of ins and outs, for what's marketed as a "desktop interface. Two mic / line inputs, one of which can also accept an instrument input (via the separate "DI" 1/4" jack socket; most other manufacturers' units accept instrument inputs within the same combo-XLR inputs, via FET-input opamps, but i digress) with send/return connectors for inserting effects or other processing before the analog-to-digital conversion, two pairs of analog outputs, a headphone output, and an optical input/output pair (each of which can be independently switched between ADAT and S/PDIF).



Not that i'm shallow, but... (especially) for a product that retails around $350 (if not more)... Do you really want or expect the logo to be nothing more than a crappy little sticker? Only to have it start to peel off on its own, after a couple years? I guess silkscreening just "wasn't good enough"(?).

After removing a few screws, and all the washers and nuts off the jack sockets, the faceplate lifts out with all the guts mounted to it. 

And we get a first spoiler, near the middle ribbon connector - "XMOS BOARD". To be fair, they've pretty much cornered the market in the low-to-midrange USB audio interfaces; 

MOTU and i suppose RME roll their own ARM / FPGA-based solutions (and perhaps Focusrite in the Clarett series?), but their products stretch into the 4-figure price range as well, so it's not 100% a fair comparison, perhaps. And that's without getting into the more "esoteric" of brands...



But what greets us is the analog output / power / converter board, the largest one inside the unit. The components are all on the visible side, but we'll get back to this later...





Removing said board, we end up getting mooned. Onwards and upwards, or... something-something.

The smaller of the boards is the digital / processing side. Quite cute of them to have included "diagnostic" LEDs for each of the five power rails present on the board, as well as for the PLL lock.

The DC input, apart from branching off to the converter board, is fed straight into a National Semiconductor / Texas Instruments LM2670 5V buck-regulator. The two SOT23-5 packaged parts are a pair of voltage detectors / reset generators - the "SCJRYP" is an OnSemi NCP303 3V-threshold detector, while the "SDERYK" is the same chip but with a 0.9V-threshold.






Hidden amongst much taller through-hole components is a tiny little NCP1521B buck converter, most likely in charge of the 3.3V rail.


After having spent a good few hours scouring the web, for the life of me i couldn't make out the marking of the 6-pin chip (nevermind identifying it), outside of the FairchildSemi logo. I could've sworn the "PH1AB" on the top row would be the marking code, and the "2012" below it, a week-year date code. I even ended up looking up lists of discontinued FairchildSemi chips, in the hope of getting at least a bit closer. With a bit of google-fu i managed to stumble upon this feature on the most complete(?) SMD marking database i've found so far - a pretty long list of chips, listed alphabetically, and with a short description that would ease filtering the dead-ends right off the bat. Out of some level of desperation, i ended up looking for images of a FAN2002 chip, and happened to find one on LCSC's website. The second row on that chip said "2002". Well i'll be damned - that means this little bugger is a FAN2012... This one's used to regulate a 1V rail, most likely for supplying the core of the Xmos controller.

Speaking of which, the Xmos chip that was so rudely given away right at first glance, is an XS1-L16A-128-QF124-C10 - now there's a mouthful. Took a while to decode the "SK1302L2C5" marking on top of the chip, ended up digging up Xmos's latest list of device markings. Next to it is an SMSC / Microchip USB3318 transceiver handling the USB interface (shocker, isn't it?), powered by an OnSemi NCP699 1.8V linear regulator. . The firmware is stored inside an Adesto AT25DF041A 4Mbit / 512Kbyte flash memory chip.

Off to one side we see a familiar face (as it were) - the "2PLC" marking indicating a "classic" Cirrus Logic CS2300 PLL. Between that and the 13MHz quartz crystal is a small single OnSemi NC7SZU04 inverter, employed as an oscillator.

The only other chip of note is a MAX11601 4-channel analog-to-digital converter, its inputs being the two potentiometers on this board (one for the "master" volume, and one for the headphone output).



Now, it's about time to get back to the analog in/out and conversion board, and take a closer look. I've got to hand it to them, it's kinda cute how they deliniated each "stage" in its own little silkscreened perimeter, and with its own group of component designators. Easier to reference components in the design stage, i suppose, as well as prototyping and troubleshooting. One thing i'm not impressed with is the way all the through-hole capacitors look like they were soldered by a blind apprentice in a hurricane.

Even less impressive is the capacitor selection in a relatively "upmarket" unit such as this: Jamicon (bearable, i suppose), "LH.Nova" (never heard of these), Fujicon (haven't heard good things). And these are that much more baffling when contrasted with all the brand-name silicon, and Murata RFI filters etc. *sigh* Well, profits gotta come from SOMEwhere, right?








The main power controller on this board is a Linear Technology LT3439 - an interesting little beast, allegedly very low-noise, push-pull converter. Oddly enough, it seems to have been designed to run open-loop (without any feedback), the output voltages relying merely on the winding ratios of the transformer. This is in charge of creating the +/- analog voltages for all the opamps, the 5V rail for the audio converters, as well as the phantom power rail. The latter also includes a regulating Zener diode.






The two other regulators present are marked "H110" - i tried for a while, but didn't manage to figure out what part number these correlate with, so yeah... Sorry. Either way, my best guess is these handle the 5V analog voltage for the converters.







The conversion of the two analog inputs to digital is handled by a TI / Burr-Brown PCM4220, while the buffering opamps ahead of its inputs are a pair of JRC NJM8080's. As are the other nine opamps on this board, in fact.



The digital-to-analog conversion is done by a trio of TI / Burr-Brown PCM1798's.








The headphone amp is a mostly-discrete solution, employing a pair of BC317's and a pair of BC337's






And now, for the "piece du resistance" - behold, and hail to the almighty Audient console preamps, and discrete JFET DI...

As opposed to the converter board, the two opamps here are a pair of TI NE5532's. Also, i can't help but get the feeling that this board was (and needed to be) manually retouched. I can't imagine how a reflow machine could create such a glob of solder on the end of an 0603-size component (CA3, in this case, as well as CA14, DA4 etc). Or hey, maybe their subcontractor's manufacturing process is just that "finely" tuned... To once again quote AvE - "It's pretty... Pretty ugly..."





Bow down, mere mortals, or else suffer the wrath of the discrete JFET DI!... Oh wait, no, it's just a boggo J112. Wow... 10 cents/pc @ 1000pcs. How come a TL072 couldn't do the job just as well? Too undistorted, perhaps? Then again, there's also bragging rights to think of...



Now, being the curious "masochist" that i am, i took the liberty of lifting the schematic of virtually this whole board. The two preamps are identical, apart from the multiple-switch 1/4" jack on input 2, for the high-impedance buffer part. For sanity-checking, i used the component designators for channel 1, but shoehorned in the instrument buffer as it's connected on channel 2.

Not exactly what one might call "rocket science" - a variation on a classic theme, albeit with a couple twists. More like a 2-in-1 sort of deal (a compound differential pair of transistors "on top" of a differential pair), with the discrete section (at least partially) within an opamp's feedback loop.


And that about sums it up for the guts of this thing. Coming up soon, the repair. Hopefully, anyway...