Hi,
I've been reading and troubleshooting for a while this problem and now I ask you for some help. I have little knowledge about designing audio stuff so my own troubleshooting is also very limited.
The project
I want to build a 5.1 system for the living room, mainly for movies but also for music. I may adapt a design and layout a PCB, print it and build it, but for now I'll start with these Chinese modules if possible. I don't need top of the notch high tech stuff but I would like to enjoy using the system.
Here's the testing workspace:
The amplifier is a 6 channel TPA3116 board, 2 in mono (sub and center) + 2 in stereo (others), and the preamp is a 5.1 mixer/crossover with NE5532. The preamp pots are (left to right): sub cutoff frequency, sub gain, center gain, rear gain, front gain, master gain. The master gain looks to be at the input.
The problem and what I've done
I have what sounds to be a ground loop or maybe it's just EMI. It just sounds the same any ground loop sound we can find on the web. Please let me know if you want me to record it.
The amp has the ability to connect/disconnect the audio signal minus to the power ground. If disconnected the hum slightly lowers but then I have lots of a noise similar to this video: Dual TPA3116 board: Fixing the AWFUL noise floor. - YouTube. All other tests are with these connected. The ground coupling between amp and preamp is only on the the flat cable that connects them. No earth connection anywhere. The audio input is my mobile phone.
- If I touch some places, the noise increases, like: RCA board flat cable input; pots; some capacitors; output flat cable (slightly);
- If I touch some places, the noise almost goes away, like preamp's ground points.
- When my phone is connected to the input, the noise is almost gone but still there (previous tests remain the with the phone connected).
- If I disconnect the input flat cable, the noise lowers but it's still there.
- If I turn the respective channel's pot, the noise is almost gone at 50-70% and keeps almost the same until 0%.
- If I turn the master gain, it looks the noise fades linearly with the position.
- If disconnect the audio connection between the amp and the preamp all the noises goes away.
After my (web) research it sounds like it's a ground loop but I have so few connections that I can't see the loop. After my tests, I believe it's just EMI and I have no clue on how to fix it anyway. It may be related with channel gains' pots, maybe? Either way, the only way there is no hum and only white floor noise is by disconnection the preamp from the amp.
I've also tried to find a preamp (with 5.1 mix/crossover) schematics to throw this one away but I couldn't. So, if any one knows a schematics I can use with these features, I'll consider it a solution too (and it will be a easier to troubleshoot anyway).
Thank you for you help!
I've been reading and troubleshooting for a while this problem and now I ask you for some help. I have little knowledge about designing audio stuff so my own troubleshooting is also very limited.
The project
I want to build a 5.1 system for the living room, mainly for movies but also for music. I may adapt a design and layout a PCB, print it and build it, but for now I'll start with these Chinese modules if possible. I don't need top of the notch high tech stuff but I would like to enjoy using the system.
Here's the testing workspace:
The amplifier is a 6 channel TPA3116 board, 2 in mono (sub and center) + 2 in stereo (others), and the preamp is a 5.1 mixer/crossover with NE5532. The preamp pots are (left to right): sub cutoff frequency, sub gain, center gain, rear gain, front gain, master gain. The master gain looks to be at the input.
The problem and what I've done
I have what sounds to be a ground loop or maybe it's just EMI. It just sounds the same any ground loop sound we can find on the web. Please let me know if you want me to record it.
The amp has the ability to connect/disconnect the audio signal minus to the power ground. If disconnected the hum slightly lowers but then I have lots of a noise similar to this video: Dual TPA3116 board: Fixing the AWFUL noise floor. - YouTube. All other tests are with these connected. The ground coupling between amp and preamp is only on the the flat cable that connects them. No earth connection anywhere. The audio input is my mobile phone.
- If I touch some places, the noise increases, like: RCA board flat cable input; pots; some capacitors; output flat cable (slightly);
- If I touch some places, the noise almost goes away, like preamp's ground points.
- When my phone is connected to the input, the noise is almost gone but still there (previous tests remain the with the phone connected).
- If I disconnect the input flat cable, the noise lowers but it's still there.
- If I turn the respective channel's pot, the noise is almost gone at 50-70% and keeps almost the same until 0%.
- If I turn the master gain, it looks the noise fades linearly with the position.
- If disconnect the audio connection between the amp and the preamp all the noises goes away.
After my (web) research it sounds like it's a ground loop but I have so few connections that I can't see the loop. After my tests, I believe it's just EMI and I have no clue on how to fix it anyway. It may be related with channel gains' pots, maybe? Either way, the only way there is no hum and only white floor noise is by disconnection the preamp from the amp.
I've also tried to find a preamp (with 5.1 mix/crossover) schematics to throw this one away but I couldn't. So, if any one knows a schematics I can use with these features, I'll consider it a solution too (and it will be a easier to troubleshoot anyway).
Thank you for you help!
Last edited:
I have deleted your URL for an image because not only was it blank but it is also pushing the margins into the next room
as you can see.Please attach images correctly like this:
How to attach images to your posts.
Attachments
Hi. Some scope images.
All scope images were taken with the setup as you see on first post's picture, except no input flat cable connected and amp's input signal ground coupled to power ground. Measured at amp's sub out and will all pots at max, unless otherwise stated.
1: all pots at max, touching no where;
2: ", touching any pots's shaft;
3: ", touching any ground point;
4: main volume at 50%, no touching;
5: main volume at 0%, ";
6: sub gain at ~50%, ";
7: sub gain at 0%, ";
8: all pots at max, measuring preamp's sub out;
9: disconnected preamp from amp, measuring sub out;
10: ", measuring preamp's sub out.
After this I can see the 50hz noise is mostly on the preamp. I can also see that the noise is most affected by each channels' gain and no so much by main volume.
Does any of this makes sense?
All scope images were taken with the setup as you see on first post's picture, except no input flat cable connected and amp's input signal ground coupled to power ground. Measured at amp's sub out and will all pots at max, unless otherwise stated.
1: all pots at max, touching no where;
2: ", touching any pots's shaft;
3: ", touching any ground point;
4: main volume at 50%, no touching;
5: main volume at 0%, ";
6: sub gain at ~50%, ";
7: sub gain at 0%, ";
8: all pots at max, measuring preamp's sub out;
9: disconnected preamp from amp, measuring sub out;
10: ", measuring preamp's sub out.
After this I can see the 50hz noise is mostly on the preamp. I can also see that the noise is most affected by each channels' gain and no so much by main volume.
Does any of this makes sense?
Attachments
I think this one may sort itself out once you:
1. mount everything in a metal chassis connected to audio ground via the RCA jacks, with pots screwed in.
2. twist your secondary-side wiring properly
3. get power transformer leakage current addressed (how is the TPA3116 supplied?) - try connecting power supply ground to a maybe 10 nF Y2 rated capacitor to protective earth (PE), obtained via a corresponding 3-conductor mains cable.
1. mount everything in a metal chassis connected to audio ground via the RCA jacks, with pots screwed in.
2. twist your secondary-side wiring properly
3. get power transformer leakage current addressed (how is the TPA3116 supplied?) - try connecting power supply ground to a maybe 10 nF Y2 rated capacitor to protective earth (PE), obtained via a corresponding 3-conductor mains cable.
Thanks for the help!
1. I confess I got demotivated once I notice the noise and didn't even bother to put everything together in the box. I'll try that soon!
2. I'm not sure how to twist these 3 wires and I couldn't find any useful info on that too. This is a centered tap transformer. Can you please give me a hint?
3. The TPA3116 is supplied with a 24V SMPS with the PE connection floating by now and the ground (V- or 0V) connection is coupled to the preamp's ground on the TPA3116 board by a solder jumper. If I connect PE to the SMPS PE through a capacitor, how do I connect the chassis ground to the PE - I mean, to which side of that capacitor? FYI, my home doesn't have PE on most outlets.
4. Should I be worried about screwing the SMPS case and the transformer directly to the chassis?
1. I confess I got demotivated once I notice the noise and didn't even bother to put everything together in the box. I'll try that soon!
2. I'm not sure how to twist these 3 wires and I couldn't find any useful info on that too. This is a centered tap transformer. Can you please give me a hint?
3. The TPA3116 is supplied with a 24V SMPS with the PE connection floating by now and the ground (V- or 0V) connection is coupled to the preamp's ground on the TPA3116 board by a solder jumper. If I connect PE to the SMPS PE through a capacitor, how do I connect the chassis ground to the PE - I mean, to which side of that capacitor? FYI, my home doesn't have PE on most outlets.
4. Should I be worried about screwing the SMPS case and the transformer directly to the chassis?
If the noise goes away when the amp and preamp are separated, then the issue must be something to do with improper grounding between the amp, preamp, and power supply. Linking grounds through a capacitor doesn't sound right. Try measuring the voltage between "grounds" and DC OV with an AC voltmeter. Maybe the switching supply allows some AC leakage through, possibly due to EMI/RFI filter caps or just capacitance between transformer windings. Try a lowish ohm resistor between DC OV and the PE.
Did you fix it?
Did you solve this? I am running into a very similar issue and would like to know if you ended up fixing it, thanks!
Did you solve this? I am running into a very similar issue and would like to know if you ended up fixing it, thanks!
I'm trying to find people with that preamp. Can you tell me what happens if I connect a stereo input to the 2.0 input of the preamp? There isn't a switch to change input, so both the 5.1 and the 2.0 input are forwarded to the output at the same time? Also, how does that 2.0 input behave, are the low frequencies forwarded to the sub (so essentially a 2.1) or are that input only going to the front stereo speakers?