What’s behind the improved sonic performance in the third-generation Amazon Echo Dot?
When Amazon evolved the Echo Dot from the short-lived first-generation design introduced in March 2016 to the second-generation successor that same October, the changes were relatively minor. I noted in my second-generation device teardown published nearly three years ago that:
The most obvious difference between the generations is the presence of dedicated “up” and “down” volume buttons on the successor’s topside, replacing the twist-top volume control, also seen on the first-generation Echo (a design change presumably done both to reduce cost and improve reliability by simplifying the unit’s mechanics, not to mention its take-apart viability). Amazon also took advantage of the generational uptick to reportedly improve the unit’s far-field voice recognition capabilities, although both designs contain a seven-microphone array (versus, notably, only two MEMS mics in Google’s Home Mini).
One area where Amazon didn’t make second-generation improvements was with respect to the unit’s audio output quality. While acceptable for synthetic voice-response purposes, to call the rudimentary speaker inside (iFixit’s dissection also has pictures) “high fidelity” would be an atrocity. And the only means to squeeze any semblance of acceptable music playback out of the second-generation Echo Dot involved placing it in a much larger enclosure, such as ones from iHome and Vaux (several of each I happen to own).
Thankfully, the sonic situation got much better with the third-generation Echo Dot, unveiled in September 2018; so much so that I have a paired set handling the midrange and highs in my office, with an also-paired Echo Sub tackling the low frequencies. The aesthetics have also evolved (or devolved, depending on your perspective, and on whether or not you prefer the predecessor’s more “industrial” cosmetics). The newest fourth-generation model is even more radical in its looks although given how common it’s seemingly become to bracket-mount Echo Dots to walls, vertically mate them to power outlets, and the like, I suspect the “friendlier” (for such configurations) third-generation model still has a notable life ahead of it.
And speaking of pairing, it’s something (whether a simple “stereo” set or additionally sub-supplemented) that the third-generation model is first-time capable of handling. To what degree does this enhancement reflect upgrades to the electronics inside, versus a corporate decision to not back-port the feature to prior-generation models (thereby encouraging owner upgrades to newer units)? And more generally, what’s behind that improved sonic performance? Let’s take a look.
As usual, I’ll begin with some box shots:
Ordinarily, I’d obscure the MAC address shown in the image, for privacy purposes, particularly since this unit came from Amazon pre-configured for my account and primary Wi-Fi network SSID-and-password. But I daresay it’s probably not going to return to fully functional form post-dissection (though I’ve been surprised before), if for no other reason than the inevitably present Faraday cage(s), whose tops I’ll need to rip off in order to see what’s inside. Along similar lines, I went into the Alexa app and removed this particular unit (identified by its MAC address) from the registered-device list.
“Unzipping” the sticker allows you to open the top of the box and lift out the plastic-swathed Echo Dot, which is the first thing you’ll see. There’s not much else left in the box, just two diminutive pieces of documentation, along with (underneath them) the AC adapter:
Here are a couple of closeups of the AC adapter, showing its specs and “barrel” connector:
Back to the Echo Dot; here’s the unit after removing the protective plastic, as usual accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison:
The Echo Dot is 3.9” (99 mm) in diameter, 1.7” (43 mm) tall, and weighs 10.6 oz. (300 grams). It comes in Heather Grey (shown), Charcoal (near-black), Sandstone (near-white), and Plum (pink) color options. Clustered along the circumference are a DC power input jack alongside a 1/8” (3.5 mm, to be exact) analog “stereo” audio output jack:
Here’s a top view, showing the up/down volume, microphone-mute, and “action” buttons:
And now for the rubberized “foot” on the bottom of the device:
That “foot” is a generally reliable access path to the insides; let’s see if it pans out this time (assisted by a flat head screwdriver to pry it away from the chassis):
In addition to the four T6 Torx screws, you’ll note an access portal to a cluster of test points on the PCB underneath.
I suspect that they find use not only for final test post-assembly but also for programming of the latest-and-greatest firmware version, along with the customer’s Amazon account and Wi-Fi network credentials if the “Link device to my Amazon account to simplify setup” option is selected during the purchase process.
Let’s get those four screws off, as-usual ably assisted by my iFixit 64-bit driver kit, shall we?
Remember the round plastic plate that the rubber “foot” had been glued to? Here’s what its other side looks like, now from the inside, complete with an RFID tag (likely used to keep track of the unit as it moves through the various assembly, warehousing, and shipping processes) and surrounded by the grey (excuse me, Heather Grey) plastic mesh from which the speaker’s sound emits in a 360° surround pattern:
And speaking of the 1.6” full-range speaker, here it is, prominently visible (along with the primary PCB, of course) in the top-half assembly that also emerges into view after the screws normally holding the two halves together in place are removed:
Even at first glance, you can tell it’s a much more meaningful transducer than that in the second-generation Echo Dot predecessor. Here’s another view of the top-half assembly, revealing another glimpse of the power input and analog audio output connectors:
Detaching the PCB from the remainder of the assembly was relatively straightforward. First, disconnect the flex PCB cable (which I’m guessing handles primary PCB power and signal communication with both the four top-side switches, the microphone alongside each switch, and the LED ring surrounding all of them):
Now remove the three screws (again, T6 Torx) that attach the PCB to the assembly underneath it:
And away we go!
This particular side of the now-free primary PCB is relatively unmemorable, that is unless you’re into passives and test points:
Flip the primary PCB over, and things get more interesting (at least to this digital-leaning guy):
First things first: note terminals P1 and P2. Now look back at the assembly post-PCB removal and you’ll see two matching “landing pads.” My guess is that this is how the amplified positive and negative audio signals transfer from the PCB to the speaker, meaning that there must be a DAC and (likely class D) amplifier on the PCB somewhere. Look closely and indeed you’ll spy Texas Instruments’ TAS2770.
Also dominating the landscape are the power input and two-channel analog output connectors. And of course, in the center there’s a previously forecasted Faraday cage. Prying it off reveals more pink thermal transfer “stuff” to be thumbnail-removed. Sigh…
And finally the ICs inside come into clear view:
Mediatek’s MT8516BAAA application SoC is the “brains” of the system (thereby explaining why I’m calling this the “primary” PCB), based on a 1.3 GHz quad-core 64-bit Arm Cortex-A35 processor cluster. Interestingly, it’s a downgrade (at least on paper, and at least from a clock speed standpoint) from the 1.5 GHz quad-core Arm Cortex-A53-based MediaTek MT8163 in the second-generation Echo Dot. Alongside it is a SK Hynix H9TQ32A4GTMC module combining 1 GByte of DRAM and 8 GBytes of NAND flash memory in a single package; another teardown of the third-generation Echo Dot found a similar multi-chip memory “sandwich” from Samsung (the KMFN60012M-B214) inside.
Next, let’s get the remainder of the top assembly … disassembled. I removed the two T6 Torx screws that had been underneath the PCB prior to its removal. I even removed the four Phillips screws holding the speaker in place:
But nothing was budging. In frustration, I examined the assembly one more time and finally noticed the two additional deeply recessed T6 Torx screws on either side of the speaker. The iFixit Torx socket set (as before) wasn’t up to this particular challenge; fortunately, however, I’d already bought the Torx screwdriver set, which was.
Removing them didn’t get me inside the assembly (although the glimpse of the speaker wiring and where it was routing confirmed my earlier audio terminal pair suspicion); the black plastic portion is seemingly solidly glued to the metal portion. It did enable me to get the topside control panel off the other side:
First step: detach the other end of the earlier highlighted flex PCB cable (whose destination, I’ll not-so-humbly note, I’d also correctly guessed before):
Next step: pop the top off another Faraday cage:
Third step: once again, remove even more thermal transfer stuff. Underneath you’ll find a MediaTek MT7658CSN dual-band Wi-Fi and Bluetooth controller, whose dual embedded antennae are on either side of it, at the edges of the PCB:
Fourth step: get rid of that white plastic ring, held in place by four more T6 Torx screws, so we can see what’s underneath:
The 12 multicolor LEDs around the circumference are now clearly visible. They’re managed, I’m guessing from the visible routing paths, by the IC in one corner labeled “T4125 3236A” (whose identity eludes me … ideas, readers?). In the opposite corner is a 74LCX74 dual D-type positive edge-triggered flip-flop which others have postulated controls the microphones’ mute function. And between them are two Texas Instruments TLV320ADC3101 stereo ADCs, each also integrating an embedded DSP, which convert and pre-process the microphones’ (the four gold-colored MEMS devices near the edge, one in each quadrant) outputs.
Flip the PCB over and there’s more to see:
Note, for example, the through-holes for sound to enter the microphones on the other side of the PCB. The switches for up and down volume control are comparatively rudimentary; the microphone control one on the left has an LED on either side, which illuminate in red (along with the red ring around the unit) when the Echo Dot is in mute mode. And I’m betting that alongside the switch on the right is an ambient light sensor to modulate the LEDs’ output based on environmental illumination conditions.
Finally, here’s the underside of the topside panel that those switches and microphone pass-through holes mate to, with a translucent ring around the edge to allow the LEDs’ output to shine through to the outside:
Last but not least, I’ll draw your attention to this excellent piece by Brian Dorey wherein he described his attempt to hack the Echo Dot. He was ultimately unsuccessful, at least up to the point where he pressed “publish” on his post, but the wealth of hardware and software info he still discovered is quite outstanding.
And with that, dear readers, I’ll put my microphone on mute, unmute yours, and await your thoughts in the comments!
This article was originally published on EDN.
—Brian Dipert is Editor-in-Chief of the Embedded Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.