Fosi General FAQs

• It is unable to rename its Bluetooth ID permanently.

• However, you can rename the Bluetooth name through your device's settings.

• Such as Android/iPhone phones: Settings > tap on the connected device you want to rename, enter a new name.

• When Android phone is disconnected but not forgotten, you'll still see the new name and can click to reconnect. If you forget the device from the Bluetooth list and then re-add it, it will be recognized as 'Fosi Audio'. The iPhone can save the updated name.

It is not possible to add a password to the device. If others pair your device, please ensure that your devices remain connected to them to prevent others from searching for them. Please remove the antenna (if included) and use the metal shell to cover the amplifier to shorten the connection distance. To disconnect from others' devices, please shut off the amp and then power it on again. In the upgraded version, BT20A PRO and MC101, you can disconnect a previously connected Bluetooth device by long-pressing the volume button for 5 seconds.

The plug of the power adapter will match the country of your delivery address.

Our supplied power adapter works within a voltage range of 100 to 240 volts.

• Adjust the audio balance levels in the settings.

• Computer: open Settings > Sound > Fosi Audio, and change the left and right balance levels.

• iPhone/Android: open Settings > Accessibility > Audio/Visual > Balance, slide the horizontal slider to the left or right to adjust the balance between the left and right audio channels.

• Ensure all cables are connected properly and plug the microphone and headphone into the corresponding ports.

• Confirm that "Fosi Audio" is in USB input mode, and note that it does not support the microphone in OPT and COA input modes.

• Make sure the headphones support the microphone function, as some headphones do not. In computer settings, go to "Settings-Microphone-Allow access to your microphone" to turn on the microphone permission for the audio device.

• Set the "Record" in the computer's sound settings to "Fosi Audio". In the sound settings, go to "Record" and select "Fosi Audio".

• Try a different USB power/data cable with OTG function.

• Use a different USB port.

• Try different headphones.

• Change a different microphone/headphone adapter cable.

• Check if the volume is turned up.

• Clean the computer, as plugin interference may cause partial functionality loss.

• To check if your microphone is working properly, you can go to the Sound settings and navigate to the Input tab. From there, you can select Test your microphone and speak into the microphone. If the blue bar rises and falls as you speak, it means that your microphone is working correctly.

• All cables are securely in place and correctly connected.

• Try different power supply.

• ①RCA OUT: Cross-check left & right speakers and input cable.

• ②Headphones out: The jack plug of the headphones does snap into place properly. Try different headphones with stereo jack and 3.5mm jack cable.

• If it has multiple input modes, try other modes to see if the issue persists. If multiple output modes, confirm if the other outputs are working properly.

• Try to connect it to different sources (output stereo, not MONO), output and cables.

• All cables are securely in place and correctly connected.

• Test away any interference devices, maybe the “noise” is possibly related to placement around some other audio gear (e.g. wifi repeater, phone).

• Try different power supply (e.g. Q4->plug it into a 5V 1A/2A adapter).

• If it has multiple input/output modes, try other modes to see if the issue persists.

• As for noise from headphone output, try to plug in a 3.5mm ground loop noise isolator and use a higher impedance headphone.

• Try to connect it to different sources, output (speakers and headphones) and well-shielded cables.

• All cables are securely in place and correctly connected.

• Test away any interference devices (e.g. wifi repeater, phone).

• Try different power supply and socket.

• If it has multiple input/output modes, try other modes to see if the issue persists.

• Check if the noise is still present when the input is disconnected.

• Try to connect it to different sources, output and cables. Try connecting to ground isolator.

• Test the turntable on another preamplifier to check if it has the same buzzing sound through the speakers.

• If it is a tube preamp, re-seat the tubes, switch them, try a spare pair of tubes.

• Ensure all cables are connected properly and that the headphone cable is fully plugged into the headphone jack.

• Adjust the volume levels on both the DAC and audio source.

• Try using a different USB cable (e.g. Q4->USB power cable and PC-USB cable with OTG function; K5 PRO-> USB cable with OTG function), multiple USB ports and with another source.

• Try using different headphones.

• Try using a different headphone microphone two-in-one adapter (if included).

• Test if the issue persists when connecting speakers to the RCA output.

• Check if the issue is still there when connecting to the TV via optical or coaxial input.

• Make sure the headphones are fully inserted into the jack and that the connection is secure.

• Check that the Fosi Audio is selected as the default audio output device on your computer or device.

• Try adjusting the volume levels on both the DAC and your computer or device.

• Try using different audio sources and input methods to see if the problem persists.

• Test with a different power/data cable.

• Try using different headphones and a 3.5mm jack cable. (If the DAC comes with a Headset Microphone Two-in-one Adapter cable, replace with another splitter cable)

• Test the other output methods (such as RCA out) to see if the issue is specific to the headphone jack.

• BT30D: The Sub out is limited to transmitting bass frequencies only. The sub frequency and volume controls apply to both passive and active subwoofers.

• BT30D PRO: Instead of a dedicated Sub out, the BT30D PRO features a full-range signal port called 'Pre out', which can be connected to either active speakers or subwoofers. When connected to a subwoofer, it delivers low-frequency signals when you set the crossover control on your subwoofer. However, the sub frequency and volume controls only apply to passive subwoofers and do not control the bass frequency or volume of active subwoofers through the Pre out.

• Ensure a stable electrical environment.

• Confirm all are plugged correctly.

• Make sure to replace the power supply and socket.

• Ensure that correctly power on the machine.

• If it is a tube preamp, re-seat the tubes, switch them, try a spare pair of tubes.

• Please refer to the video through the link. https://youtu.be/9bObE2Z24Eg (1:33 Preamp)