Teardown: Hi-Fi Audio Amplifier with Bluetooth

In this teardown, we examine the Lepy LP-168 Hi-Fi Stereo USB Audio Amplifier with Bluetooth, by NKTECH.

At a Glance

The advertised features of this Hi-Fi audio amplifier include:

• Overload, short circuit, and overheat protection
• Internal high quality Bluetooth module
• USB-BT (Bluetooth)
• Electronic volume control
• RCA input and output
• Input voltage DC 19V-24V
• Infrared remote control
• 2.1 channel sound output

Prior to tearing into this product, my first thought was how well-built this unit appears including its professional-looking aluminum enclosure. 

NKTECH's Lepy LP-168 Hi-Fi audio amplifier with Bluetooth.

Lepy LP-168 (front view).

Lepy LP-168 (back view).

 

The included AC to DC power supply also feels like a quality-built device along with its professional looking label (pictured below) appearing to have all the necessary compliance marks.

Included AC/DC battery with all the necessary compliance markings.

Let the Dissection Begin

To remove the aluminum enclosure, both Phillips and Torx (size T7) screwdrivers are required. With these screws removed, the amplifier's guts simply slide out of the outer enclosure. Below, you can see the top side of the PCB assembly.

 

PCB assembly top-side.

 

As can be seen, the overall design is not too complicated. Because all the electrical components reside on the top-side of the PCB, this design philosophy is referred to as a single-sided PCB. The phrase "single-sided PCB" should not be confused with the number of PCB layers—this design has two layers, which are top and bottom; no internal layers. Utilizing a two-layer design reduces cost and should be used whenever possible. The single-sided PCB philosophy—that is, populating components on only one side—is also a cost-savings tactic.

The PCB's bottom-side includes no components:

PCB assembly bottom-side.

 

Now you might be asking, what about that huge IC right in the center of the PCB. Well, that component is not actually attached (soldered) to the bottom side of the PCB. Rather, it resides on its own separate (green) PCB, which has been installed perpendicular to the main (black) PCB. If you look closely at that big IC you may see white thermal grease. This thermally conductive grease helps transfer heat from the IC to the outer aluminum enclosure.

White thermal grease on the inside of the enclosure is used for transferring heat from the IC to the enclosure.

The logic for why this second smaller green PCB is used escapes me. I would think that soldering the big IC to the bottom side of the main PCB would be less expensive than designing, buying, and installing the second PCB. Also, not all board houses (aka, PCB manufacturers) have the capability for cutting a slot in the middle of a PCB, though most high-volume board houses do have this capability—but perhaps a premium may be charged as it requires special cutting and drilling bits.

One more thing about that huge IC; you might have noticed that it's actually the only IC that uses the aluminum case as a heat sink—this should tell us something important about this particular part

Taking a Closer Look at the PCB and its Components

The top side of the PCB has yet another PCB mounted to it. This smaller PCB contains the four pushbuttons—Mode, Prev, Play, and Next—as well as the IR receiver device, which is an optoelectronic device.

Also, resistors R39 (connected to Mode), R40 (connected to Prev), R41 (connected to Play), and R42 (connected to Next) all have different resistance values. This approach allows a single I/O port, of a microcontroller, to monitor all four buttons simultaneously as the different resistor values will produce different voltages depending on which button is depressed. An alternate approach would be to assign an individual I/O port to each of these four buttons, which, in this case, would be quite inefficient regarding the use of I/O ports. This is a very novel approach—nice job!

Also observable is red ink on the two bolts and nuts. Ink applied in this fashion (the ink can be any color) represents that proper torque has been applied to these screws. Basically, this ink is representative of good quality control measures. Nice work!

A smaller PCB attached to the main PCB.

Again when viewing the image above, four pins are visible of which are connected to both PCBs. These interconnecting pins are used to transfer signals, voltage, and ground between the two boards. Employing such pins, instead of wires or a ribbon cable, is an effective cost-savings approach.

The image below shows five turning knobs, or potentiometers. All five potentiometers, or pots, as they are commonly called, are marked B50K.

• "B" represents the linear taper type. Taper simply means the relationship between the position of the potentiometer and the resistance ratio.
• "50K" represents 50kΩ, which is the resistance range.

Front side of unit—five turning knobs.

The ICs

This audio amplifier system uses only five ICs:

ICs identified on main PCB.

1. Audio Power Amplifier. This IC is made by STMicroelectronics and has the IC marking TDA7379. This IC alone allows this audio amplifier system to produce the power that it's capable of. More so, this high-power capable device is the reason for why it uses the white thermal grease for transferring heat the case.
2. Voltage Regulator. This L78M05 device, also from STMicroelectronics, is a high-precision 500mA 5V voltage regulator. It supplies 5V to the "brains" IC as well as to the USB connector.
3. The "brains" IC. Although this IC is clearly marked—JL AC1701AP0W625-1A8—no datasheet could be located. However, this IC definitely serves as the intelligence of the system as it appears to be a microcontroller with built-in Bluetooth capabilities—the Bluetooth antenna connects to it.
4. NPN Transistor. This transistor has part marking Y1.
5. Dual Op Amps. This JRC4558 device, by Artschip, is a high-performance monolithic dual operational amplifier.
    

Main PCB

The main (black) PCB looks to be a high-quality board. It's a double-sided PCB (no internal layers) with rather hefty power and ground planes which are necessary given the high-power capabilities of the system. The board thickness is 0.062" (62 mils) which is an industry standard.

Although the color green is the default/standard color for PCBs, black is also an industry standard. Most board houses offer a variety of PCB colors, including black, blue, white, and red.

Conclusion

The Lepy LP-168 Hi-Fi Stereo USB Audio Amplifier with Bluetooth, by NKTECH, has the look and feel of being a high-quality product, including its assembly, chosen materials, and completed fit-and-finish—all the parts are solidly connected and the overall product is aesthetically pleasing. Without having schematics and layout files available, the design itself looks to be adequate for the low price of $46.99.