VS1053 output very quiet when connected to external amplifier

[tagrobotics]

Hello,

I would like to request some input on an issue I seem to be facing with this VS1053 based board here. In a nutshell, I'm working on a home project based on an ESP8266 NodeMCU, which I programmed to stream MP3 real time from internet radio stations, directly to the board I mentioned. After a lot of programming and debugging, the stream now works perfectly and I can listen to it using headphones without issues. When I use the headphones, the sound quality is great and the volume is really loud at the highest setting.

However, this project is not for a headphone, so right now, I'm in the process of moving this thing to a custom radio shell, and I would use a 2.1 Speaker system, with its existing Class D amplifier to play the music. However, when I connect the input jack of sound system (which is the input of the amplifier) to the VS1053 board output, the sound coming from the speaker is barely audible. Even if I turn the pot of the amplifier to the max, I can only hear it clearly if I'm within the same room. Which is a bit weird, since connecting the sound system input to my phone output or a laptop playing some MP3s or pretty much everying else, yields a very clear and loud sound from the same system.

Some other info about the amplifier board: It seems to have a high performance stereo amplifier chip, which is unfortunately covered by a big heatsink, so I don't know the exact type. It also has another amplifier chip (TDA2822), which I can only assume acts as a pre-amp in this circuit. Also, since this is the stock amplifier that was installed in the box of the subwoofer, it is proven to be the correct one for the system. This circuit is powered with 9V.

Things I've tried so far:
- Check power supplies => even with stable and plentiful power, the same issue happens. Power supplies of the sound system (9V) and the NodeMCU / VS1053 (5V, 2A) are completely isolated.
- Briefly connect board GND instead of "GBUF" to the input of the amplifier, along with L/R => sound gets loud, but also VERY distorted and somehwat slowed down (????). To be fair, this confuses me, especially the latter part.

So to sum it up:
Connecting VS1053 to headphones -> clear audio, good loudness.
Connecting VS1053 to 2.1 external amp and speakers -> clear, but barely audible audio.
Connecting any other sound output I know to 2.1 external amp and speakers -> clear and earth-shakingly loud music

Now, I did hear that since the VS1053 is meant to have a headphone output therefore VBUF (+1.23V?) is connected to the SPK jack, along L and R instead of GND. However, could this cause this problem at all? If I understand correctly, it would more likely cause noise/distortion on the output from the speakers, something that I don't seem to have at all. Any pointers on how to fix this problem would be really appreciated... Thanks in advance!

[pasi]

DO NOT connect GBUF to an external amplifier's ground. Unless your player is on battery operation (so that the GND of the player is not connected to GND of the amplifier), it causes the GBUF to drive 1.2V to GND, which causes vs10xx to drive a large current.

Fortunately this will trigger the driver protection circuit and turns off the analog drivers.

With an external amplifier you need a line output connection. See here: viewtopic.php?f=9&t=69

[tagrobotics]

Thanks for your reply. Yes, I only did that initially when I thought the jack output of the Geeetech board was L,R and GND as well. Not doing that again for sure I'll try and reproduce the circuit you refer to and see how that goes.

[tagrobotics]

Update: I finally had time to get the appropriate resistors and capacitors and whip up the circuit. Thanks a lot for the suggestion, it works really well. However, I have one more issue right now: even after filtering, there is a high pitch - I assume narrow band - noise that I can hear in the background. It is hard to tell which frequency, but I think it should be around 800-1000Hz. This is pretty much constant, doesn't go away when I play anything and is also there when nothing plays. However, increasing the volume increases the noise and vice versa. I tried using different power supplies for the amplifier and the vs1053, but it had no effect. I'd appreciate any feedback. Thanks in advance!

[pasi]

If there is nothing to decode and the audio FIFO is starting to be quite empty, vs1053 will insert 32 zero samples to it. Depending on the samplerate this happens for example at 44100Hz/32=1378Hz, 32000Hz/32=1000Hz, 22050Hz/32=689Hz.

Other times the vs1053b is just doing nothing and waiting for DAC interrupts. Every 32 samples it would draw more current, which could cause interference.

However, this should not be affected by the volume control. Zero should be zero with any volume setting.

[tagrobotics]

Update on this issue, the noise seemed to be a result of a grounding/isolation problem. After a review on my connections and some changes it seems to be finally gone and the sound is clear now. Thanks for the support!

[pasi]

Great! It's good to be well-grounded.