Hi all. First time poster here 
I used to be an EE major but that was a looonnng time ago and I've forgotten most of what I knew
I've got a simple audio amplifier. Doesn't have a ton of power, and fidelity isn't great, but it suits my needs in this situation.
Connected as a source to the amplifier is a little bluetooth receiver. When the items first arrived, I hooked them up and they worked exactly as I'd hoped, and it really sounded pretty good!
Turns out the inside of the amplifier has just enough room to put the bluetooth receiver inside, so I cracked them both open and got to work.
The amplifier runs on 12v, so I wired up a 7805 to power the bluetooth off of the amplifier's power supply. Then ran 3 wires to connect the bluetooth headphone out jack to the amplifier line in jack (both 1/8" audio jacks).
Fired it up and nothing exploded, bluetooth powered on, amplifier powered on, and my phone connected and was playing music. But there was a high-pitched whine added in. Very noticeable even with music playing.
First I disconnected the right audio, then the left. The whine got significantly quieter, but didn't go away -- it was present in both the left and right signals. Then I reattached the audio and disconnected the 5v supply (removed the 7805) and powered the bluetooth independently (isolated) from the amplifier. The whine was still there (still softer)
Then I disconnected the bluetooth entirely, powered it separately, and connected the audio with a standard cable just like I did when they first arrived. The whine is still there (still softer). WTF??
What am I doing wrong? How do I fix it?
Thanks in advance!!
I used to be an EE major but that was a looonnng time ago and I've forgotten most of what I knew I've got a simple audio amplifier. Doesn't have a ton of power, and fidelity isn't great, but it suits my needs in this situation.
Connected as a source to the amplifier is a little bluetooth receiver. When the items first arrived, I hooked them up and they worked exactly as I'd hoped, and it really sounded pretty good!
Turns out the inside of the amplifier has just enough room to put the bluetooth receiver inside, so I cracked them both open and got to work.
The amplifier runs on 12v, so I wired up a 7805 to power the bluetooth off of the amplifier's power supply. Then ran 3 wires to connect the bluetooth headphone out jack to the amplifier line in jack (both 1/8" audio jacks).
Fired it up and nothing exploded, bluetooth powered on, amplifier powered on, and my phone connected and was playing music. But there was a high-pitched whine added in. Very noticeable even with music playing.
First I disconnected the right audio, then the left. The whine got significantly quieter, but didn't go away -- it was present in both the left and right signals. Then I reattached the audio and disconnected the 5v supply (removed the 7805) and powered the bluetooth independently (isolated) from the amplifier. The whine was still there (still softer)
Then I disconnected the bluetooth entirely, powered it separately, and connected the audio with a standard cable just like I did when they first arrived. The whine is still there (still softer). WTF??
What am I doing wrong? How do I fix it?
Thanks in advance!!
