1
\$\begingroup\$

I have built a Bluetooth speaker (based on this Instructable), which works except there is a faint clicking noise in the background. This is a basic diagram of the circuit for the speaker: enter image description here

I am almost certain that the problem is caused by a ground loop, because I have tried using a separate power supply for the Bluetooth adapter and this fixes the problem. However, I need to be able to power the speakers and the Bluetooth receiver from the same battery.

I read online that someone else fixed a similar problem by adding an audio transformer to the left and right channels. I tried using an NTE1 1:1 audio transformer, and this did not help. With the transformer connected the speaker was actually worse, because it only made static noise and did not play audio.

If the problem is indeed a ground loop, I would not really expect an audio transformer to fix it because the problem is with the power wires rather than the audio wires. I think a ground loop isolator would solve my problem, but when I researched them online, the only products I saw were adapters made to be used with audio systems like this.

This is probably a really noob question, but I am not sure how to fix the ground loop problem with just small circuit components. How would I go about this?

\$\endgroup\$

closed as off-topic by Chris Stratton, Blup1980, Elliot Alderson, stefandz, Dwayne Reid Jan 15 at 23:32

  • This question does not appear to be about electronics design within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 4
    \$\begingroup\$ You assume a ground loop, but that might not be the problem. You need to verify the cause, and then fix it. You could spend a lot of time chasing your assumption if the problem is really something else. \$\endgroup\$ – JRE May 11 '17 at 9:12
  • 4
    \$\begingroup\$ I'm voting to close this question as off-topic because it is an XY problem which has been abandoned by the asker \$\endgroup\$ – Chris Stratton Jan 12 at 20:59
3
\$\begingroup\$

Probably RFI rectification by the amplifier.

There are a few things you can do: 1) Twist your wires into twisted pairs, this will lessen the effect of magnetic field loops.

enter image description here

2) Use inductive ferrites to increase the inductance of the cables, high frequency currents take the path of lowest impedance. Using a ferrite on the cable can block high frequency signals

3) Shield your wires or your project (this is more expensive) Shielding provides a faraday cage which could block most of the high frequency signal from getting close to your electronics.

4) Shunt the high frequency currents back to the source, use capacitors (RC filters) to shunt the high frequency currents back to the source before they reach sensitive parts of your circuit.

\$\endgroup\$
  • \$\begingroup\$ Since using separate power supplies for the speakers and Bluetooth receiver fixed the problem (when nothing else was changed), doesn't that prove that the cause is a ground loop? If RFI rectification was the problem, I wouldn't expect that to have fixed it because I didn't do anything to filter out high frequencies. \$\endgroup\$ – tjohnson May 11 '17 at 10:53
  • 2
    \$\begingroup\$ You don't know how the noise is getting into your signal. Grounding systems are a problem for two reasons 1) because they make a large loop antenna 2) because they create common mode noise from currents shared between two devices. Since you don't know if its a ground loop, or something else, you have to try all methods. In most products dc wires are twisted (if they aren't shielded) to eliminate EMI or RFI. If you have a large loop between the return current (ground) and the source current in wires, do your best to eliminate it. \$\endgroup\$ – Voltage Spike May 11 '17 at 14:38
1
\$\begingroup\$

Putting an isolator (such as CME0303S3C) inline with the power input on the bluetooth module should fix this problem:

https://www.mouser.com/ProductDetail/?qs=XKx0tEJeiQ3UXTrSkJqzTw%3D%3D

\$\endgroup\$
  • \$\begingroup\$ Thanks, I actually ended up doing that after finding a YouTube video that suggested it. Unfortunately there is still some noise present, even after adding the isolator. \$\endgroup\$ – tjohnson Jan 20 '18 at 2:12
1
\$\begingroup\$

Connect ferrite beads series with Vcc power GND and analog GND, preferably close to the BT-module! (50-100ohm @100MHz will do) You also can add big (10uF) X7R ceramic capacitor between bluetooth module's power supply and GND pin, right at the module. It helps a lot with my BT-module.

This buzzing noise is not due to ground loop. The problem is that 577Hz BT pulse rate is audible, but it is come from RF current spikes on the ground. Ferrite beads and bypassing stop these spikes.

\$\endgroup\$
0
\$\begingroup\$

Bluetooth earpieces can suffer from the 577Hz RF pulse rate. Manufacturers have learned to prototype these circuits and pick OpAmps that are adequately immune to local RF fields.

\$\endgroup\$
  • \$\begingroup\$ Sorry but this answer isn't helpful. I'm trying to figure out how to fix a ground loop in the circuit. \$\endgroup\$ – tjohnson May 11 '17 at 3:49
  • \$\begingroup\$ Look at the other answer, by laptop2d. That answer is continuing what I discussed. \$\endgroup\$ – analogsystemsrf May 11 '17 at 7:11
-1
\$\begingroup\$

i had a similar problem on my Bluetooth receiver where it made screeching noises so i put a 100uf capacitor over the positive and negative power terminals but then my Bluetooth receiver burnt out the next days so maybe try this with your amp?

\$\endgroup\$
  • 1
    \$\begingroup\$ I'm confused - are you suggesting for someone try a "fix" that may have contributed to the failure of your device? \$\endgroup\$ – mike65535 Jan 12 at 20:42
  • \$\begingroup\$ only if you wish im almost positive that the capacitor didnt bust my receiver but it may have \$\endgroup\$ – josh b Jan 13 at 5:59

Not the answer you're looking for? Browse other questions tagged or ask your own question.