Fosi Audio BL20C is a powerful Bluetooth 5.0 HiFi stereo 2.1 channel amplifier with AUX/Bluetooth/U-disk inputs and Treble and Bass control to meet more your needs. 

Product Specifications
Product Overview & Control Functions
Package Contents​
Quick Steup
Warranty Information
About Fosi Audio

Product Specifications

Fosi Audio BL20C is a powerful Bluetooth 5.0 HiFi stereo 2.1 channel amplifier with AUX/Bluetooth/U-disk inputs and Treble and Bass control to meet more your needs. It supports MP3/WMA/APE/FLAC/WAV music formats, suitable for most home passive speakers. Adopting classic TDA7498E chip to get clear sound without any audible noise even at high output.

Input mode



output mode

Active subwoofer +  Passive Speakers


Input priority

U-disk>Bluetooth = AUX








Frequency response



Working voltage



Speaker impedance




USB 2.0, compatible with USB 3.0


U-disk capacity

Up to 32GB, no more than 100MB per file


Support format



Max output power

160 watt x 2 @4 ohm

Product Overview & Control Functions

Package Contents​

Fosi Audio BL20C Amplifier *1
AC Power Cord *1
24V/4.5A Power Supply *1
Bluetooth antenna *1
User Manual *1

Quick Setup​


Prepare 1: BL20C, 24V power supply, passive speaker, active subwoofer, speaker wires or banana plugs, RCA cable;

Prepare 2: Make sure the volume is at a minimum.

Prepare 3: Connect passive speaker via the speaker wires or banana plugs, and connect active subwoofer via 3.5mm AUX cable, please pay attention to distinguish between positive and negative polarity.

Prepare 4: Make sure the power switch is on the “OFF” position.

Prepare 5: Connect the power supply and turn it on, the power indicator shows red light.

Note: Please make sure that the power switch is in the OFF position before connect the power supply.How to connect the speaker wire?Method 1: Bare wire connection illustration

① Release the horn terminals block terminals;

② Insert the two ends of the speaker wire into the amplifier and speaker terminal holes;

③ Tighten the horn terminals;

Note: Please make sure that the speakers’ wire are not attached with each other, the speaker connection area is very narrow. It is easy to cause the positive and negative speakers’ wires to contact each other, which will result in no sound output.

Method 2: Connection of banana plugs (Figure)

① Release the banana jacket;

② Loosen the screw;

③ Insert the speaker cable and tighten the screw;

④ Tighten the banana plug;

⑤ Insert the banana plug into the horn terminals of the speaker and amplifier.

Note: Please make sure that the speakers’ wire are not attached with each other, the speaker connection area is very narrow. It is easy to cause the positive and negative speakers’ wires to contact each other, which will result in no sound output.

Bluetooth input

Prepare your Bluetooth device (take a phone as an example)).

Step 1: Install the Bluetooth antenna.

Step 2: Switch the input mode to "BT/USB" position, the "BT/USB" indicator will be blue.

Step 3: Turn on Bluetooth on your phone and connect "BT HIFI AUDIO".

Step 4: Open the audio application, play and enjoy!

AUX input

Prepare: audio source (take a TV as an example), an RCA cable.

Step 1: Switch the input mode to the "AUX" position, the power indicator will be red;

Step 2: Connect your TV to the "Audio Input" via RCA cable;

Step 3: Open your TV, play and enjoy!

U-disk input

Prepare: one U-disk

Step 1: Switch the input channel to the "BT/USB" position, the "BT/USB" indicator shows the blue light.

Step 2: Insert the U-Disk into the "USB" port on the front panel, and the BL20C will automatically detect the music format of the U-Disk.

Step 3: Short press the "PREV", "NEXT" or "P/M" buttons on the front panel of BL20C to select or pause your songs.

Note: The capacity of the U-Disk for the BL20C should be less than 32 GB and no more than 100 MB per file.Note: Make sure there is no Bluetooth connection. If there is, please press and hold the "P/M" button to switch to USB mode.


1: What type of speakers work best with BL20C Amplifier?

  • Fosi Audio BL20C amplifier work great with any 4-8 ohm passive speakers. But please be attention that the amplifier is for passive speakers and an active subwoofer, not for active speakers.

2: Can I connect turntable to BL20C amp, why is the volume is extremely Low?

  • As for the turntables do not have a built-in preamp, if not connect to a phono preamp first, the volume would be low.
  • As for the turntables which have a built-in preamp, you can connect directly to the BL20C with the turntable.

3:  Why does the sound is cracking or makea lot of electric noise?

  • Please make sure all the cables completely pushed into the devices, incompletely connection will cause this cracking.
  • Please remove all the inputs then check whether cracking noise disappear or not, the cracking maybe from the audio source or input cables.
  • If you are not using the original factory standard power supply, please replace the power supply before testing. Many power supply in the market have large interference coefficient,  which will cause a lot of current sound.

4: My Bluetooth device cannot pair with BL20C?

  • Ensure that you have selected the input channel to “BT/USB” on the front panel of the BL20C, and the “BT/USB” indicator shows blue light.
  • Make sure there is no U-disk on your device because U-disk takes priority over Bluetooth.
  • Make sure that BL20C is powered on.
  • Make sure that BL20C is not paired with other devices.
  • Ensure that the distance between your device and BL20C is not too long.
  • Make sure there are no barriers between your device and BL20C, barriers will affect the Bluetooth operation distance.
  • Please reconnect the power supply to the BL20C, and move the BL20C to another room to have a try.
  • Restart the BL20C and then try to connect again, try to use other Bluetooth devices.

5: Why is Bluetooth intermittent?

  • Please try with another Bluetooth device.
  • Ensure there is no interference from other electronic devices between the BL20C and your audio source.
  • Place your device close to the BL20C, and plug in the power adapter again.

6: How much power does it take in standby mode? Can this amp be left on all the time?

  • This is the class D amplifier, and it will cost low power when it is in standby mode. It can be connected all the time, and it is safe without power consumption.

7: Is the sound quality not good?

  • Make sure all the cables are fully connected.
  • Adjust the treble and bass control of the power amplifier to achieve the right tone.
  • Please try to change the sound source and cables to test.

8: Can BL20C accept a signal from a Bluetooth microphone?

  • Please make sure your Bluetooth microphone must be the transmitter. Because BL20C is a Bluetooth receiver amplifier.
  • Please ensure that the microphone’s Bluetooth can be connected to the BL20C’s Bluetooth by your operation.

9: Why does the sound cut in and cut out?

  • Please try to change the sound source.
  • Lower the treble and bass of the BL20C.
  • Make sure that the positive and negative terminals of the speaker outputs do not touch each other. Some of the larger banana plugs can easily touch each other and cause a short circuit.

10: Can I bridge channel 1 and channel 2 to get 320 watts?

  • No, this amplifier can’t be bridged.

11: Why does distortion occur?

  • When the output power of the BL20C exceeds the typical output power, there will be significant distortion. If you turn the sound up too loud, distortion may occur. Please try turning the volume down a little.

12: Why does my power indicator not light up?

  • Please check that the AC power cord is securely connected to the power supply and an AC power outlet.
  • Please check that the AC power outlet is supplying power. Make sure the power LED on the power supply will stay on.
  • Please replace another power supply and try it again. 19-35V DC power supply is suitable.
  • If you make sure the power supply is defective, don’t hesitate to contact us for an exchange.

13: How can I use BL20C to create a 2.1-channel system? 

  • You can connect two passive speakers via “SPK OUT” and one active subwoofer via “SUB OUT” to create a 2.1 Channel system.
  • Please use an RCA cable to connect your active subwoofer to the “SUB OUT” output port.

14: Can I connect Bluetooth and U-disk at the same time?

  • No, when the U-disk plugs in, the Bluetooth connection will be interrupted.

Input priority: U-disk Input > Bluetooth Input15: How can I connect BL20C to TVs?

  • The RCA jack is the audio input on the back panel of the BL20C. It can be connected to your TV via RCA cables.

16: Why is there no voice from my speakers?

  • Please make sure the input mode you select is consistent with your input method.

Note: If you use U-disk, please make sure the capacity of U-disk should be under 32GB, and no more than 100MB per file.

  • Please check whether the power supply cable is connected to BL20C and whether the power indicator is on.
  • Ensure the BL20C’s indicator light is on when the power is turned on.
  • Please check that the BL20C and your source components are turned on and not set to minimum volume. If possible, replace your source and test again.
  • Check that the wire connections from the audio source to each speaker in the amplifier are connected correctly.
  • Please check that the cable and your U-disk are not loosened or damaged. Incomplete connection is one of the main reasons for no sound.

17: Does BL20C support aptX-HD and aptX-LL?

  • No. BL20C does not support aptX-HD and aptX-LL.

18: One channel does not work?

  • Please test whether the Bluetooth and RCA input have the same problem first.
  • If the two modes have the same problem, swap the speaker cables of the left and proper channels, change another speaker, and then test whether this channel still does not work.
  • If only RCA or Bluetooth mode does not work, change the audio source, change the RCA cable and test again, and make sure that all the wires are completely pushed into the device.n

Warranty and Maintenance

  • All Fosi Audio products have an 18-month limited warranty on parts and labor from the date of purchase. Please contact us if you have any problems.

About Fosi Audio​

  • Fosi Audio designs and builds innovative audio products with all your music in mind. Great sound, simple but elegant designs, high-quality materials, and truly useful features are what Fosi Audio is about. We sincerely hope you get as much enjoyment from our products as we’ve had to create them!

Our website:

Amazon store: 

Our Youtube channel: Fosi Audio

Our Facebook page: Fosi Audio

WhatsApp: +8613716612254

Call us: +49 33389171782

After-sale Service and Technical Support Email: