Headphone Amplifier with Bluetooth

ClippyTheDiode

ClippyTheDiode

Well-known member
I added Bluetooth to my Headphone Amplifier. The upper right toggle turns the module on/off and the blue LED shows BT module status. I wired in a 7805 voltage regulator to power the BT module with 5V. 10k resistors were used between the BT module output and the wipers of the Dual POT. There is a little bit of audible noise (clicks and chirps) during the quiet parts but once audio is playing, (guitar or BT) it just drowns out the noise. The regulator and BT modules are stuck to the main PCB with double sided foam tape, and a tack of e6000 on the corners. Even with the case closed it connects to my phone just fine.
 

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Any issues with delay between the transmitter and receiver? I have tried a couple of BT modules but always had unacceptable delays with different sets of BT headphones.
 
zgrav said:
Any issues with delay between the transmitter and receiver? I have tried a couple of BT modules but always had unacceptable delays with different sets of BT headphones.
Click to expand...
The bluetooth is just for audio from my phone to the headphone amplifier. I use it to play along with youTube tab videos or youTube Music etc. So if there is a delay I can't tell. I still use a wired set of headphones from the amplifier, so my guitar signal is real time.
 
ClippyTheDiode said:
The bluetooth is just for audio from my phone to the headphone amplifier. I use it to play along with youTube tab videos or youTube Music etc. So if there is a delay I can't tell. I still use a wired set of headphones from the amplifier, so my guitar signal is real time.
Click to expand...
That is a really good idea.
Having two audio sources doesn't mess with the sound output?
 
ThePanda said:
That is a really good idea.
Having two audio sources doesn't mess with the sound output?
Click to expand...
Thanks.
I didn't have a schematic for the circuit, so I just guessed. I looked for the input to the LM386. I wasn't sure if I should connect them with resistors or capacitors. I figured it was a 10k pot, so I would start with 10k resistors. I guess it kind of works like a blend knob. In operation first I set the headphone amp volume knob where I want my playing level to be, then start the backing track on the phone and adjust its volume. I usually end up at about 9 to 12 oclock on the headphone amp, and about 50% to 75% volume on the phone.
 
ClippyTheDiode said:
... There is a little bit of audible noise (clicks and chirps) during the quiet parts but once audio is playing, (guitar or BT) it just drowns out the noise...
Click to expand...
Your BT addition inspired me to do this to my Headphone amp as well!
Have you tried putting a 0.1uF cap on the voltage reg output to get rid of the audio noise?

I found this in the datasheet.
lm78m_app.PNG
 
ThePanda said:
Your BT addition inspired me to do this to my Headphone amp as well!
Have you tried putting a 0.1uF cap on the voltage reg output to get rid of the audio noise?

I found this in the datasheet.
View attachment 48191
Click to expand...
I have a 10uF SMD cap on the output, if I remember correctly. I think most of the noise is coming from the antenna being so close to the main PCB.

Right now I have a piece of double sided foam tape between the BT module and the PCB. I was thinking I may try adding a layer of copper tape and hook it to ground. So the stackup would be PedalPCB-> Foam Tape-> Copper Foil (hooked to GND)-> Foam Tape-> BT Module.

Ideally, the best answer would be to get the antenna outside of the metal enclosure. But I can only hear the noise when nothing is playing so I have just been using it as is for now.
 
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