With everything going wireless it comes as no surprise that even speakers are using Bluetooth! In this Teardown Tuesday, we will strip down a Sony Bluetooth Speaker to see how they are put together and what parts they consist of.

Key Parts

  • IS1690 Bluetooth module IC

  • ESMT AD52580 audio class D amplifier

  • GT432A 2 wire serial EEPROM

 

The Bluetooth Speaker

The speaker has three faces with grilling (most likely for airflow for the internal speaker), a top side with buttons, a back side for IO connections, and a base that contains information regarding the product's specifications.

It can be used either wirelessly via Bluetooth and the pair button or it can be used with a standard 3.5mm audio cable. The top-side of the speaker that contains the interface buttons includes a power button, a speakerphone button, and volume adjustment buttons.

 

The Bluetooth speaker

 

The amount of documentation supplied with the product is insane, in-depth and in many different languages. (The weight of the documentation, alone, is hefty. If you taped all of it together, it could potentially be a blunt weapon.)

 

The documentation

 

The back of the unit that contains the IO interfaces and includes an "Add" button (to work with multiple speakers), a reset hole, a 3.5mm audio port, and a USB Micro-B charging port.

 

The various io ports on the back of the speaker

 

Product information given on the bottom of the speaker includes the input requirements, model number, and company information. The base also includes four LEDs found on the perimeter of the base which communicates charging, left audio, right audio, and Bluetooth connections.

 

The label information and LED indicators

 

Accessing the Internals

Getting access to the inside of the speaker was not obvious at first. From the outside, there are no visible screws or fittings, which suggested that the unit could be either molded or sealed. However, previous teardowns show that manufacturers have a habit of hiding screws under product labels and coverings that users would not want to be damaged.

So, naturally, I ripped off the faces of each side and, as a result, uncovered many screws. The cloth-like material in the photos is actually double sided sticky tape (or something similar)—this is the only thing that keeps the faces attached to the product. Do keep in mind that this adhesive is really strong and the product could be suspended in the air with one finger being stuck to it!

 

Removing the faces reveals a sticky material

 

Locating the PCBs

Removing the screws revealed internal components. The first internal part to reveal itself was a PCB with many surface mount parts. This PCB was easily removed with a small flathead screwdriver which then revealed more parts, including the main speaker and the battery.

 

The first PCB found

 

Close-up of the PCB

 

However, there was one part that was a surprise: the ribbon cable that runs through the product. 

 

The internal speaker and wires

 

I knew this cable must be attached to another PCB, so the next task was to locate this PCB. 

As expected, flipping the unit around and removing the interface cover revealed another PCB which was held down with four screws. Interestingly, the PCB contains screw symbols near the screw holes to show what they are for. Additional information can never hurt, especially in the production line where workers need to operate as quickly as possible.

 

The second PCB found

 

Batteries

Removing the IO port side showed the battery used in the speaker which turned out to be (no surprise) a lithium-ion battery. 

 

The battery tucked away

 

What was peculiar about this battery was that it was made up of two smaller batteries and the battery had three wires instead of two. 

One of the batteries was labeled as an 8.4V battery at 1000mAh while the other battery was labeled as 7.4V at 1000mAh. Considering the use of three wires, it may be possible that the two batteries provide two different voltages with a common ground reference. This can be advantageous when the speaker can affect the supply enough to cause problems in microcontroller circuitry.

 

One battery

 

The other battery

 

The two batteries combined

 

The Interface PCB

The PCB that sits underneath the top side (the side with the buttons) has four PCB tactile switches, many test points, and many stitching via.

The PCB, from the bottom side, also shows a cutout on the top left which is for the Bluetooth module that sits on the underside. The cutout is needed as to prevent mitigation of the radio signals sent from the module while the many stitching via are used to prevent stray EM waves from leaving the module. This is imperative for EMC compliance as opposed to the functionality of the device. In other words, the product would most likely still work without the stitching via but not including them would result in the device potentially interfering with other nearby circuits.

 

The interface PCB's top side

 

The PCB shown here has many test points, a feature usually only found on higher-end products. This is because cheaper products (which have an emphasis on frugality in production) are less interested in electrical testing of the PCB before and after production. However, higher-end products are expected to work consistently (especially right out of the box) and so are usually scrutinized during testing to ensure that only functional units are shipped.

The test points shown here are gold-plated and large in diameter which makes it easy for both human and robotic testing. 

 

Various test points and stitching via visible on the top side

 

The side of the PCB also contains eight drilled holes (also gold plated) which may be for programming the Bluetooth module (assuming that the module is also being used as the main controller). 

 

The possible programming port for the Bluetooth module

 

The topside of the PCB reveals many surface-mount components, ICs, connectors, and a module. The use of modules in PCBs (as opposed to ICs) has become increasingly popular and has some benefits over discrete ICs. Firstly, modules (if sourced correctly) are compliant with EMC laws (such as FCC and CE), which helps engineers considerably when trying to improve EMC. Secondly, modules are more expensive than discrete parts but they are usually self-contained and all the circuitry needed to make them work is included and therefore easier for the engineer to design. For example, there is no need to design an antenna, choose component parts, and they are easy to prototype with. 

 

The underside of the interface PCB

 

The Bluetooth module

 

One nice feature of big brand names such as Sony is their use of standard parts which are easily identifiable. In this case, the Bluetooth module is the IS1690 (PDF) which is produced by Microchip. This is a Bluetooth speaker solution which includes a microcontroller, audio processor, audio codec, many internal peripherals such as an integrated 3V and 1.8V LDO and a high-speed UART. All of this is packaged into a 7mm x 7mm 56 QFN package.

 

The main IC, the ISSC IS1690SM

 

Next to the main IC is a GT24C32B-2ZLI-TR, the TSSOP package of the GT24C32B (PDF), which is a 2-Wire 32K-bits (4KB) serial EEPROM. This most likely stores information such as host and connection details.

 

The serial memory, the GT432B

 

The Analog PCB

The PCB that contains the IO ports is connected to the first PCB via a ribbon cable. This PCB also handles USB charging and external audio via the 3.5mm audio connector. The underside of the PCB shows many surface mount parts and test points but, unlike the interface PCB, these test points have been soldered. The reason for this is that this PCB contains through-hole parts and was wave soldered (presumably to keep costs down). Since wave soldering does not discriminate a test point from a component leg, the test points were also soldered.

 

The IO port PCB underside

 

The top side reveals many components including ICs, through-hole connectors, electrolytic capacitors, possible inductors, and many surface-mount devices. 

 

The analog/power PCB topside

 

Two ICs on the top side cannot be identified but have the identifications ASVSNA and XJ50H. Considering their proximity to the electrolytic capacitors, one may be an audio device that amplifies the final output analog signal while the other could be a mixer that chooses between the signal from the Bluetooth and the 3.5mm input.

 

The ASVSNA can be seen on the left (small QFN IC)

 

The XJ50H IC

 

The third IC of interest is the ESMT AD52580 (PDF), a Class D 20W audio amplifier, which puts the theory about the other ICs to rest. The datasheet also helps to reveal what the two black components next to it may be as the datasheet suggests that the outputs to the speaker(s) have ferrite bead filters. The 150 will, therefore, relate to the inductance which could be 15uH.

 

The ESMT AD52580 Class D audio amplifier

 

The last main IC on the topside of the PCB is labeled as ASIC AS4558 which does not show up when scouring online resources and thus the function of the IC cannot be determined for sure. The Bluetooth module receives digital audio information and, considering how sending audio signals over cables is not typically desired, the PCB here is probably receiving digitally-encoded audio signals. This IC, therefore, could be a serial device that converts I2S into an audible signal.

 

The ASIC AS4558

 

Summary

This Bluetooth speaker demonstrates many manufacturing techniques behind higher-end products where testing and verification are important.

The many test points show a potentially vigorous testing stage where signals are fed into the PCB and the results are recorded to see if they match up with results of a proven circuit. The use of fiducials and soldered test points shows the reliance on mass production techniques as well as the goal of removing human intervention as much as possible. The use of screw symbols on the PCB also show an interest in keeping employees on the production line from making mistakes and preventing individuals from using initiative (this was a serious problem where I used to work).

This speaker was incredibly well built and the quality of the PCBs clearly demonstrates the benefits of professional work.

 

Next Teardown: WorkTunes Hearing Protection Headphones

 

Comments

1 Comment


  • ronbot 2017-05-26

    Really nice teardown, and great pictures!

    In Li-Ion battery packs (which, BTW, are made of multiple CELLS, not multiple batteries, since by definition a battery is a group of cells) the 3rd wire is for temperature monitoring. Li-Ion cells have a limited “safe charging temperature” range, this wire is used to provide the charging circuit this information.

    The different printed voltages has to do with “typical operating voltage” (typ. 7.2V), and maximum charged voltage (8.4V). Different national regulations require different printed specifications. Li-Ion cells vary in voltage quite a bit over their SOC (State of Charge) range… from 4.20V (per cell) at 100% fully charged voltage, down to around 3.0V when fully discharged. If they are allowed to drop below 3.0V, permanent damage to the cell may result (this varies slightly between mfr’s and specific Lithium cell chemistries)  This is why it’s never good to let a Li-Ion cell/battery to fully discharge… as it will shorten it’s useful lifespan. “Best care and feeding” of Li-Ion is to charge as often as possible… the charging circuit will shut off the charge current as needed, and prevent overcharging.

    Too bad you broke that one cable - this usually happens if you pull on the wires, instead of using a small tool to unplug the connector. Sometimes you can use the open jaws of small flush-cutter diagonals to separate the male/female halves… sometimes a very small jewelers screwdriver can be used to gently pry them apart at the sides of the connectors, between the two halves… one side, then the other - back and forth until it comes apart.