This is an old thread, an industrial solution is found. Please visit this thread.
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Greetings! About 7 months ago, I posted a thread about the noise from a bluetooth audio receiver.
Link to the thread: https://www.diyaudio.com/community/threads/bluetooth-audio-receiver-high-frequency-noise-hum.375580/
Unfortunately, none of the solutions in the thread can fully eliminate the noise, and I also didn't find any solutions from the forum. Recently, out of some random chances, a professor from my university mentioned sth about common mode choke, said that it is a component to build a EMI filter, and that's literally how I find the solution to my problem.
I know that there are a lot of people working with bluetooth audio receiver had faced the same problem, then ended up using a more expensive bluetooth module. Therefore, 7 months later, I am here to share my solutions that might eliminate the noise from your Bluetooth audio receiver.
It will be brilliant that we can read till the end of this post as I would love to share my personal best solution for building a Portable Bluetooth Speaker for discussion!
Identifying the problem
First of all, we need to identify which types of noise occurs on your system.Generally speaking, there are two types of noise can occur with the Bluetooth audio receiver:
I have made audio demonstrations for your reference.
- Low Frequency Buzz
As the name suggests, the noise is in a low and constant frequency.
- High Frequency Hum
A humming noise in high frequency. Sometimes the noise is dynamic, the frequency might be phrasing/varying, the noise might be softer after some time.
This two types of noise actually corresponds to different problem of your system and it is possible for both noises to occur. If the noise from your bluetooth receiver is very different than what I have suggested, it could be either your bluetooth receiver is defective, or it's simply too cheap... Yet if that wasn't the case, you are very welcome to discuss with everyone in this thread.Possible Solution
Low Frequency Buzzing
If this is the type of noise that you are hearing, there is a good chance that you connected the bluetooth module and the amp from the same power source. And the noise will be gone if you supply the bluetooth module with another battery or any other power source.The buzzing that you are hearing is caused by the current draw of the bluetooth receiver, and since amp is connected with the same power source, the noise from the receiver can feedback to the amp from its power input (from its GND specifically). We call this problem a Ground Loop Noise, or Non-Isolated Ground Feedback Noise.
To solve this problem, you will need a DC-DC Isolator connecting between the power supply and the bluetooth receiver to isolate the bluetooth receiver and the amp.
Sth looks like this:
There are isolators with different rated values, make sure that you use the right one for your receiver.
There are also isolators that can isolate and step up of down the voltage from the power source, you can use one when needed, but I personally would not suggest that. I will explain why later.
For more information about Ground Loop Noise, I have came across a video from GreatScott!
High Frequency Humming
This is the noise that occurs from my last project, took me long enough to find the solution. sighThis noise is a bit complicated. It is due to the interference from the Bluetooth signal of the Bluetooth receiver. Although the frequency of the bluetooth signal is way too high for the amp to pick up (2.4GHz), the amp can pick up and playback the lower harmonics of the interference, yet we are still talking about frequencies around MHz, that's why we can hear the humming keeps phrasing with the amp's frequency response. The problem that you are facing is Electromagnetic Interference (EMI). This usually occurs when you are using a cheap Bluetooth module (even on some CSR/QCC module), that's because on a more expensive Bluetooth receiver, there can be special algorithms to suppress the noise. Yet, using the component below is going to give you the best result.
To solve this problem, you will need a EMI/EMC Filter. You can either connect it between the power source and the Bluetooth receiver, or connect it between the amp power supply. The EMI Filter looks like this:
Notice that there you can find coils from the module. And that is a Common Mode Choke that I mentioned earlier.
Again, there are different rated values for EMI filters. Some of them can handle very large current, some of them are designed for low load modules.
You may use different EMI Filters at different rated values depends on your usage. If you have tons of modules connected to the same power source with the amp, just get one large power EMI Filter for your amp. If only have one module, get a smol EMI Filter just for that module as they are usually cheaper than the large power ones.
If you want to learn more about EMI filters, here is another video again from GreatScott!:
My Personal Best Solution for DIY Bluetooth Portable Speakers
Thanks for staying with me till here! Now I would like to share my experience on DIY Bluetooth Speakers.I personally like to build medium sized DIY Bluetooth Speakers, that the power of my speaker is around 20W-50W. Therefore I usually use 12V battery for the Amp's power supply. As most Bluetooth Audio Receiver are rated at 5V, I simply use 12V-5V step down DC Isolator for the job, AND THIS starts my journey to find the solution for High Frequency Humming Noise. Yup, with some reasons, the High Frequency Noise can still feedback to the amp even when there is an Isolator (probably its because the frequency is too high).
Some people didn't have this problem is because they use a DC-DC Converter to step down the voltage first, then supply the Bluetooth Module with the stepped down voltage through a isolator. And I figured out that some DC-DC Converter actually comes with designs to suppress high frequency interference or even have a built in EMI Filter. Im pretty sure that some of these people eliminate the High Frequency Humming without knowing lol.
Anyway, because of this, I suggest that using a DC-DC Converter, and a DC Isolator for the Bluetooth Receiver can be the best solution, as this will be the cheapest to DIY a Bluetooth audio to your speaker.
However, not all DC-DC Converter has great build quality or an EMI Filter, some DC-DC Converter might even generate noise to the circuit, you will need to experiment with different brands of the component to get the best solution.
Also, DC Converter is still a DC Converter, which is meant for stepping up or down the voltage source. If you would like to fully eliminate the EMI, use a EMI filter at the power input of the amp, and DC Isolator for the Bluetooth Receiver.
Why using a Big EMI Filter for the amp instead of using a smol one for the Bluetooth Receiver you ask?
Welp that's simply because I didn't find much EMI Filters for low load components from my supplier. But who knows if you can find one from your place?
And finally, that's all I want to share, this took me long enough! I have struggled for too long since I got this problem, therefore I wrote this brief instructions for everyone who would like to build portable DIY Bluetooth Speakers just like I do.
I hope this post can help you on your project, good luck on your build! 😀
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I had all sorts of bad noises trying to power BT modules from the same PSU as the amp. Any ground common to PSU and signal caused trouble. I found only two ways to kill the noises.
- Audio 1:1 isolation transformer. Worked fine, but big and somewhat expensive.
- Isolated step down chip. From amplifier supply voltage to 5V. Just like the one you show.
I was struggling a few years back to get rid of an alternator whine in my car, and the solution was a basic element that had not been mentioned in the many, many places on the internet.
I finally found mention of a simple choke made from winding the supply wire around a chunk of iron on an archived Jeep site, for the purpose of providing clean power to the CB radio.
All those fanatics on the car stereo sites, all the seasoned (diy and professional) electronics engineers/technicians on this site all seemed to fall back to the same definitive textbook ground loop rationale for an answer.
Ground loop my eye!
I finally found mention of a simple choke made from winding the supply wire around a chunk of iron on an archived Jeep site, for the purpose of providing clean power to the CB radio.
All those fanatics on the car stereo sites, all the seasoned (diy and professional) electronics engineers/technicians on this site all seemed to fall back to the same definitive textbook ground loop rationale for an answer.
Ground loop my eye!
Ikr, I've been searching this problem on the internet for a long time, and I only found one video about using an EMC filter to solve the problem. There are tons of Informations about EMC filter on internet, but not about how you can use it for your amp.
That's why I started this thread lol
The DC-DC isolating power supply looks like a good solution to my noisy BT receiver as well.
My question is where to mount the device? The easiest place for me would be inside my power supply enclosure, tapping power for it off the 12v input pads, and send a 5v cable out to the BT receiver, but would it pick up noise inside there? I could also buy a use a small plastic box and wire it inline to my BT receiver. I could epoxy it to the BT receiver, but would prefer to do such a hacky fix. Any recommendation appreciated.
My question is where to mount the device? The easiest place for me would be inside my power supply enclosure, tapping power for it off the 12v input pads, and send a 5v cable out to the BT receiver, but would it pick up noise inside there? I could also buy a use a small plastic box and wire it inline to my BT receiver. I could epoxy it to the BT receiver, but would prefer to do such a hacky fix. Any recommendation appreciated.
Thanks for this. My solution has been to use a separate power transformer or winding for powering the bluetooth module. Of course, the grounds are connected at only one point. My present system has an external bluetooth device that is powered by a wall wart. I guess it sounds as good as bluetooth can sound, but is not the best solution for every project.
Surfing the web, I saw that using audio isolation transformers is a popular workaround for DIYers, but as mentioned this approach has its drawbacks.
Vendors like Parts Express offer a lot of integrated bluetooth plus audio amplifier boards. I would be curious how these units work around the ground loop issue. Some of these boards look like an excellent value, but they all employ digital amplifiers. I know many of us don't like digital amps, so we're faced with the ground loop problem. But one of these days I'm going to buy one of those cheap and dirty boards and put together an integrated bluetooth reciever and stereo speaker unit. It won't be hard to make it better than commercially offered bluetooth speakers; I have yet to hear one that doesn't sound (at best) lo-fi.
Surfing the web, I saw that using audio isolation transformers is a popular workaround for DIYers, but as mentioned this approach has its drawbacks.
Vendors like Parts Express offer a lot of integrated bluetooth plus audio amplifier boards. I would be curious how these units work around the ground loop issue. Some of these boards look like an excellent value, but they all employ digital amplifiers. I know many of us don't like digital amps, so we're faced with the ground loop problem. But one of these days I'm going to buy one of those cheap and dirty boards and put together an integrated bluetooth reciever and stereo speaker unit. It won't be hard to make it better than commercially offered bluetooth speakers; I have yet to hear one that doesn't sound (at best) lo-fi.
I got noise from wall warts too, even supposedly good ones. Current build is for a boat- 12v so DC to DC is easy for me.
Normally, I would install it in the amplifier. It depends on your BT module, if u are using a small, cheaper module, I would rather not making an enclosure for it. But if you are using some more expensive, usually bigger in size too, and it comes with an antenna, I would make a metallic case for it.
Sure, but the point is that using a wall wart to power the bluetooth module breaks the ground loop.
As an exercise, I built an analog preamp - 2 inputs, bass and treble, and volume - designed to work off a DC wall wart from 12-30 volt. There is RLC filtering in both legs of the power input. So it will work even with a not so good wall wart because the noise doesn't get through.
My external bluetooth receiver came with a wall wart. I don't know if it's a "good" one or not (it's probably switching) but there is not a problem with noise from this unit.
You can design around a noisy power supply. 12 volts from a vehicle is a noisy source, and addressing it with chokes and whatnot has been around since the first transistorized units and maybe before that.
Big boats are very noisy indeed. Sonar, radar, big alternators, motor drives, and back EMF spikes from coils unloading all have to be filtered out as much as possible. We use a combination of shielded cables, careful hull grounding, snubbers, and lots of toroid rings to get most of it.
The ground loops are yet another problem to get clean audio. I just bought a few WSTECH DC-DC isolation converters on Ebay. I also got some cheap aluminum boxes to mount them in. So far I'm planning to leave the box ungrounded but open to suggestions there.
Here's an idea I never got far with: Is there an electronic circuit that will break the ground loop? No an audio coupling transformer or DC-DC converter, but an active circuit with op amps. Has this been done? And how do they arrange the grounds on those integrated bluetooth receiver/amplifier boards so there's no ground loop?
I have a jbl desktop Bluetooth speaker and there is no dc-dc converter module or anything.
The point that all Diyer’s including my self is that we are failing is the knowledge for ground plan.
How high frequency currents flow on the ground plane and couple on to other signals. Where and how to place cuts in the plan.
If we get proper input on the above topic than yes we could have a proper design but that is going to tough to come by.
People may restrain to explain here coz there are many manufacturers small one hanging here on such forums to exploit.
It’s sad but no solution to it.
The point that all Diyer’s including my self is that we are failing is the knowledge for ground plan.
How high frequency currents flow on the ground plane and couple on to other signals. Where and how to place cuts in the plan.
If we get proper input on the above topic than yes we could have a proper design but that is going to tough to come by.
People may restrain to explain here coz there are many manufacturers small one hanging here on such forums to exploit.
It’s sad but no solution to it.
Hey Eddie,
You are right there are opamp by TI which do the ground loop prevention. They are in the Line driver and headphone amp section for audio.
Thanks.
You mean like this? https://www.ti.com/lit/ds/symlink/d...90773&ref_url=https%3A%2F%2Fwww.mouser.com%2F
I guess it uses some kind of phantom ground?
Anyway, I was hoping for a universal solution that could use off the shelf op amps. I haven't thought about it for a while but thanks for bringing it up.
Is this how those integrated bluetooth amplifiers break the ground loop? The only game in town? As far as a turnkey chip I was hoping for something more familiar and universal (NOT 3 volt of 5 volt crap) similar to DRV134, which is easy to use (for an old school guy like me) and does a lot of heavy lifting.
You mean like this? https://www.ti.com/lit/ds/symlink/d...90773&ref_url=https%3A%2F%2Fwww.mouser.com%2F
I guess it uses some kind of phantom ground?
Anyway, I was hoping for a universal solution that could use off the shelf op amps. I haven't thought about it for a while but thanks for bringing it up.
Is this how those integrated bluetooth amplifiers break the ground loop? The only game in town? As far as a turnkey chip I was hoping for something more familiar and universal (NOT 3 volt of 5 volt crap) similar to DRV134, which is easy to use (for an old school guy like me) and does a lot of heavy lifting.
Is the JBL bluetooth speaker battery powered? The battery breaks the loop. Also, there's no ground connection on the charging cable, is there? So there's nowhere for ground currents to enter or exit.
Maybe I misunderstand and you mean ground loops within the circuit, sorry if so. There is a lot of info out there on PCB grounding/layout to reduce EMI. e.g. https://neurochrome.com/pages/grounding
Maybe I misunderstand and you mean ground loops within the circuit, sorry if so. There is a lot of info out there on PCB grounding/layout to reduce EMI. e.g. https://neurochrome.com/pages/grounding
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red
These were Desktop speakers so no battery.
Second, I am trying to say that we need to understand RF design for PCB layout and not just what Tom( he is not wrong ) suggests for the amp to be applied in the case of the Bluetooth board. _ I am still learning
We need to have a very low impedance path to ground path for one for sure. - Ground pours
We need to understand how the current flows on that board and how it would impact the other sections.
Wires do not work in this case, they may have worked for amplifiers but not here.
A 12v / 1 Amp wall wart powers the JBL speaker.
These were Desktop speakers so no battery.
Second, I am trying to say that we need to understand RF design for PCB layout and not just what Tom( he is not wrong ) suggests for the amp to be applied in the case of the Bluetooth board. _ I am still learning
We need to have a very low impedance path to ground path for one for sure. - Ground pours
We need to understand how the current flows on that board and how it would impact the other sections.
Wires do not work in this case, they may have worked for amplifiers but not here.
Yes I know how a battery or wall wart breaks the ground loop. In fact this is how my bluetooth is set up; it runs off a 12 volt wall wart.
I was speaking in general terms but specifically, how would I break the ground loop when I use a bluetooth receiver board integrated into an existing preamplifier? I've read where people use transformers to break the loop (obvious but undesirable). A separate winding on the power transformer is another easy solution if you have that option.
Or maybe I'm overthinking it? The boards I build always have a separate power and "noise" ground. I run all the noise grounds to a reference point (typically the volume control) and then one wire to the power supply ground. This works great with no ground loop or noise problems. Maybe it's that simple?
I was speaking in general terms but specifically, how would I break the ground loop when I use a bluetooth receiver board integrated into an existing preamplifier? I've read where people use transformers to break the loop (obvious but undesirable). A separate winding on the power transformer is another easy solution if you have that option.
Or maybe I'm overthinking it? The boards I build always have a separate power and "noise" ground. I run all the noise grounds to a reference point (typically the volume control) and then one wire to the power supply ground. This works great with no ground loop or noise problems. Maybe it's that simple?
Me too.
Still a mystery? I might get one of those boards and see if it works.
There still has to be a generic electronic circuit to accomplish this.
Still a mystery? I might get one of those boards and see if it works.
There still has to be a generic electronic circuit to accomplish this.