Teardown Tuesday: Hi-Fi Audio Amplifier with Bluetooth

August 15, 2017 by Nick Davis

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

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.


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.


Next Teardown: ThermoPro’s TP07 Wireless Digital Meat Thermometer

  • L
    Lopsd August 16, 2017

    The certification marks printed on the power supply are fake, not suprised btw

    Like. Reply
    • N
      ndavis17 August 17, 2017
      Hello. How do you know they are fake?
      Like. Reply
      • L
        Lopsd September 04, 2017
        hi, sorry for being late here you can check ul's certification, inside keyword put the model or the trademark, you will see nothing happens = fake. You can do the same on TÜV's
        Like. Reply
  • I
    ITFlyer August 25, 2017

    A few notes:

    - The “ink” is not ink used to identify proper torque. It is thread locking glue used to keep the nuts from vibrating loose.
    - Pots are measured in ohms, not watts
    - The power supply certification marks are counterfeit. There is no listing in the CSA database for this device, and the UL certification number printed on the label does not exist. I would be suspicious of the safety of this power supply’s design.
    - With only a 19 volt, 57 watt power supply (basically it’s a generic laptop power supply), and no visible DC-DC converter, there is no way this is a high power amp. It’s advertised as 2 x 40 watt plus a 68 watt sub channel, for a total of 148 watt output. How they are managing this with only 57 watts coming from the power supply is a miracle of physics (i.e. it’s bogus BS). I would expect actual output is closer to 2 x 10 watts, and with unlistenable THD much beyond that.

    Basically, it’s cheap junk being sold with untruthful marketing and counterfeit labeling.

    Like. Reply
    • N
      ndavis17 August 28, 2017
      Hello ITFlyer, I appreciate you reading the article and providing feedback. Thanks for pointing out the typo/incorrect units on the resistor. This error will be changed shortly. Regarding your ink comment: I used to work in an electronics manufacturing facility where thread locking glue (Loctite) was utilized. The glue was always applied to the bolt's threads prior to installing the nut (per the manufacturer's directions). Also, in the same facility we used ink to verify that torquing requirements were met. However, perhaps in this application the "ink" is indeed a glue that was either improperly applied or its a type that can be applied once the nut has been installed. -Nick
      Like. Reply
      • K
        Kate Smith August 29, 2017
        Hi, guys! The unit has been corrected.
        Like. Reply
      • RK37 August 29, 2017
        I also suspect that the ink is actually glue. I worked at a defense contractor where apparently the preferred way of securing bolts even on an airborne military system was a dab of glue (special glue, I assume) connecting the top of the bolt to the surrounding metal enclosure.
        Like. Reply
  • col_panek August 25, 2017

    In 2017, I’d expect to see a Class D amplifier. And calling it a 10 W/ch amp would be a bit more truthful. Still not a bad unit considering.

    Like. Reply
  • Navraj Singh September 16, 2019

    I have this amp and the sound is incredible considering the price of it..I have connected 4 focal component speakers in car and what an amazing sound it gives and that too on Bluetooth..just love it..and thanks for detailed info I came here while trying to find out the chipset of it..

    Like. Reply