There are many solutions for streaming audio from your computer to Bluetooth devices. One affordable Bluetooth transmitter/receiver pair is presented here. With these two Bluetooth modules, streaming audio from PC is very easy.
JDY-62 is an affordable Bluetooth stereo audio receiver module with great sound qualities for the price that works best with headphones but when using with a differential amplifier such as HW-104 (PAM8403) there will be beeping noise on the sound caused by Bluetooth communication if the ground connection is not properly made.
To send audio from PC to the JDY-62 module I have used the Bluetooth 4.0 CSR dongle transmitter that works well on Windows 10 and Linux and acts like a sound card that you can select in the media player. As the name suggests it uses Bluetooth v4 which is not as performant as v5.
With this combination the signal strength is not so good. Many times sound dropped while holding the hand over the receiver. Works great for custom Bluetooth headphones provided the transmitter is in line of sight which can be achieved with an USB extension. Not sure which is the weak link - transmitter or the receiver. Probably it will work better with a Bluetooth version 5 transmitter.
Contents
JDY-62 module pinout
1 - VCC - 5V. The module can also be powered from 3.7V (4.2V battery) by shorting the diode above the pin but that will remove the reverse polarity protection.
2 - GND - power ground and unfortunately the audio ground. Unfortunately because the high current pulses creates a voltage drop raising the ground potential and if the impedance to ground is too high it will produce modem-like sounds. For this reason the audio ground (G2 in the following schematic) must be connected as close as possible to the pin 2 (G1 in the schematic).
3 - L - left channel audio output that goes to the tip of the headphones jack.
4 - R - right channel audio output that goes to the ring of the headphones jack.
5 - MUTE - mutes the module. There is not much documentation about this but I think it must be HIGH to mute the sound and LOW for normal mode.
6 - KEY - 3 push buttons can be connected to this pin. One directly to
ground for Play/Pause, a second one through a 22k resistor for next track or
volume up on long press and a third one connected to ground through 15k
resistor for previous track or volume down on long press.
How to connect the JDY-62 Bluetooth module
C1 is a 100n ceramic capacitor for fast transients currents and C2 is for slow currents. C3 and C4 removes the DC bias and higher values gives bigger base.
Update: C3 and C4 are not needed since the board already has DC blocking capacitors but it might help eliminating ground noises.
Power ground G1 and audio ground G2 must be connected together as close as possible to the pin 2 (GND) of the JDY-62 module. The Bluetooth antenna must be kept away from any metal that could block the radio signal and the power lines should not pass beneath the antenna because that could also induce beeping sounds on the output.
Connecting JDY-62 module to an audio amplifier
The above schematic worked well for headphones but when I tried using an audio amplifier the beeping noises appeared no matter how I connected the grounds. After tinkering for a while I found out that disconnecting the audio ground (G2 in the above schematic) solved the problem and the audio was crystal clear.
In order to avoid modem-like beeping sounds or 2Hz motorboating there are a few solutions.
Method 1: An amplifier with a differential input stage
To remove ground noise, you need an amplifier board that keeps the Left and Right negative inputs entirely separated from the power ground.
Look for mini amplifier boards based on the TPA3116D2 or TPA3118 chips (often labeled as "Sanwu" boards or mini digital amplifier modules). Many of these layouts have four input pads: IN_L, GND_L, IN_R, and GND_R.
Because the input grounds are isolated from the main power ground on the board, the amplifier chip acts as a shield, rejecting the shared power supply noise generated by the JDY-62.
Method 2: Adding an "AC-Coupling Filter" to the HW-104
When using amplifiers such as HW-104 that only gives you a single shared GND pad for the audio input, you can build a cheap passive filter between the JDY-62 and the HW-104 to block the DC ground noise from crossing over.
Instead of running a straight wire from JDY-62 GND to HW-104 GND, you install two components:
A resistor on the ground line: place a 10 ohm to 47 ohm resistor inline on the wire connecting the JDY-62 ground to the HW-104 audio input ground. This creates resistance against the noisy current trying to loop between the boards.
Input capacitors: put a 1uF to 10uF capacitor inline on both the L and R audio lines before the HW-104. Even though the JDY-62 has SMD caps on board, adding these larger caps creates a barrier that forces the two boards to match their AC signals without letting the digital ground noise leak through.
Method 3: Using an isolated DC-DC converter
You can use a module such as B0505S-1W that sits on the power line right before the JDY-62. It uses an internal transformer to pass power through magnetic fields.
The amplifier connects directly to the battery ground. The Bluetooth module connects to the isolated output ground of the B0505S.
Because the grounds are 100% electrically separated, it is physically impossible for a ground loop to form keeping the background noise silent.
Method 4: Use a Bluetooth receiver with differential output
Bluetooth receiver boards with true differential (balanced) outputs exist, and they are eliminate ground loop noise when paired with a differential amplifier. Instead of routing audio through a shared, noisy ground plane, these boards provide four dedicated pins: L+, L-, R+, and R-.
Differential output Bluetooth devices (not JDY-62)
On those boards, you have four distinct audio pins: L+, L-, R+, and R-. The L- and R- pins are not connected to ground. They carry an inverted copy of the audio signal. When the amplifier's input is also differential, it used a feature called Common-Mode Rejection Ratio (CMRR) which cancels the Bluetooth noises. Any digital Bluetooth noise or power fluctuations affect both the positive and negative wires equally. The amplifier looks at the difference between the two wires, subtracts the identical noise, and leaves you with 100% clean music.
Single-ended output Bluetooth
The JDY-62 uses a Single-Ended Output architecture. It does not output a true negative signal. Instead, it lifts the audio ground up to a fake "middle" voltage (around 1.65 V) so the audio waves have room to move up and down without hitting 0 V. When you connect the JDY-62's Audio Common to the HW-104's audio ground because the HW-104 draws heavy, pulsing current to push the speakers, it shakes that ground plane. The JDY-62 has no way to subtract that noise because it isn't using a differential L- and R- setup. The amplifier amplifies the ground fluctuations right along with the music, resulting in the intense digital buzzing and the 2Hz motorboating.
Bluetooth receiver alternatives
- Qualcomm QCC-Based Boards (QCC3031, QCC3034, QCC5125).
- CSR8645 module.
- MH-M38 board hybrid that includes built-in 5W + 5W differential amplifier.
When you pair these with a true differential amplifier there is no audio ground wire connected to the power ground. The audio signals float completely independently. When the Bluetooth chip transmits data and causes power fluctuations, the noise hits the positive and negative lines at the exact same time. The differential amplifier subtracts the identical noise, leaving you with crystal-clear audio and absolute silence when paused.
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