Hello,
Some may remember my problem with DIY android tablet head unit for car from other posts.
Long story short: I get ground loop noise when powering android tablet with buck converter (stepping from 12-14v to 4.2v). I added audio ground loop isolator that made an improvement, but noise was still there.
I bought cheap oscilloscope and discovered that I have up to 600mV ripple when under load on power output of buck converter
.
I managed to minimize the ripple to about 30mV with LC filter and thats the best I could manage to do playing with different capacitors and inductors. That also helped alot with the noise.
Now to the point: Left alone the power source, what can I do to audio signal path to quiet down the noise.
If I google ground loop isolator I can see that some of them have resistors and/or electrolytic capacitors. But mine has only 2 transformers (stereo).
I also remember from DIY amplifier project I did a long time ago that someone suggested me to add some resistors from signal towards the ground to bring down the noise... it helped alot... but I can`t remember values...
So what components can I add to the audio path to hopefully see some improvements?
Thank you
Some may remember my problem with DIY android tablet head unit for car from other posts.
Long story short: I get ground loop noise when powering android tablet with buck converter (stepping from 12-14v to 4.2v). I added audio ground loop isolator that made an improvement, but noise was still there.
I bought cheap oscilloscope and discovered that I have up to 600mV ripple when under load on power output of buck converter
.I managed to minimize the ripple to about 30mV with LC filter and thats the best I could manage to do playing with different capacitors and inductors. That also helped alot with the noise.
Now to the point: Left alone the power source, what can I do to audio signal path to quiet down the noise.
If I google ground loop isolator I can see that some of them have resistors and/or electrolytic capacitors. But mine has only 2 transformers (stereo).
I also remember from DIY amplifier project I did a long time ago that someone suggested me to add some resistors from signal towards the ground to bring down the noise... it helped alot... but I can`t remember values...
So what components can I add to the audio path to hopefully see some improvements?
Thank you
Another cause can be that the power converter is 'underloaded' or to reactive/capacitive loaded. Add a substantial bleeder on its output and see if that surpress the noise.
Those resistors 'binds' the various signals to known reference points, most often the ground.
Values depends on output impedence of source and input impedance of load.
Those resistors 'binds' the various signals to known reference points, most often the ground.
Values depends on output impedence of source and input impedance of load.
Noise appears when tablet starts doing something, so when power supply is under load, would bleeding resistor still help in my case?
Cheap switcher supplies perform the best when the load approximates the rating on the data plate. So, does your table load current approximate the max the supply will put out? No? Add a parallel resistor in a suitable enclosure.
The same with cheap wall transformer supplies, too. They put out rediculously high voltages when they are not loaded to the rating.
The same with cheap wall transformer supplies, too. They put out rediculously high voltages when they are not loaded to the rating.
It's a LM2596 buck step down converter, it's stated that it has 3A max output. I can't afford to have that much current flowing because it will be running all the time in car (tablet in stand by mode when ignition turned off).
The DAC in the tablet itself is also a place to look.
DACs often produce their own noises, especially if youre using the volume in the tablet and your amps are sitting there not attenuated. You may want to try another DAC attached to the port of the tablet.
DACs often produce their own noises, especially if youre using the volume in the tablet and your amps are sitting there not attenuated. You may want to try another DAC attached to the port of the tablet.
I am using volume in the tablet with amps not attenuated, but noise is not there if I power tablet from seperated power source
OK
Input signal transformers are expensive, but would probably cure your problems.
Given the time you invest, they can also be considered cheap.
Input signal transformers are expensive, but would probably cure your problems.
Given the time you invest, they can also be considered cheap.
I'm a bit lost now. Arent input signal transformers used in ground loop isolators (transformer with same primary and secondary)?
Yes I spend alot of time on the project (custom gui, automation, dab+, etc...) but I'm struggling with that noise problem from the start, I already reduced it by 90%, at the start I had dial up modem like beeping sounds almost as loud as the music played at 3/4 volume. But that 10% is still too much not no bother me.
Another method could be to wire a relay of sorts to charge the tablet while the car is off, and then detach it from the source while running, so that it's on battery while in use.
Other things to try are to create your own lift in the signal wire. You can start by testing the wire with the ground snipped at one end. If that helps, look into creating a lift on that wire
Other things to try are to create your own lift in the signal wire. You can start by testing the wire with the ground snipped at one end. If that helps, look into creating a lift on that wire
I can`t charge the tablet because I need usb port in otg mode, because of that I removed the battery and hardwired smps to the battery input.
I snipped the ground signal wire, but the noise is much louder.
I checked the grounds on audio side. signal gnd is connected to power gnd on the amplifier, but not on the tablet if that helps anything.
Another thing I don`t understand is why I still get ground loop noise using ground loop isolator (1:1 audio transformers) if audio signal ground between tablet and amp is not connected. Are there some leakages in transformers or something? Or is it backfeeding thru power ground?
It appears to me as if some gear and devices are put together but were not initial ment to do so. All parts should be in relaible condition and cross checked in a compareble but controllable setup. Is it the tablet, the converter, a leakage, a loop, a bird, a whatever?
Use Occam's razor to shift to the options until it's found.
Another interpretation of this path is called superposition, and extremely usefull in any scientific, be it electronics in mobile or domestic fashion, analysis.
You're on the rim of a known range, the plane before you is empty. Dive or diy.
Use Occam's razor to shift to the options until it's found.
Another interpretation of this path is called superposition, and extremely usefull in any scientific, be it electronics in mobile or domestic fashion, analysis.
You're on the rim of a known range, the plane before you is empty. Dive or diy.
If the noise disappears with another power supply, I would think that would be a big part of the issue.
Have you tried an inverter? A small pure sine inverter into the adapter or power supply that you plug into the tablet?
Not sure where you are grounding your amplifiers, but would it be possible to either ground the amps and power for the tablet at the same locations?
Another idea could be to use a bluetooth adapter and place that at the amps. I forget the high bitrate kind, but I know samsung uses that high quality codec over blutooth.
Another idea is if you use an apple tablet, you can stream to a device like the raspberry pi using shairport-sync. I use that in my home setup and it's dreamy. Place a Pi at your amplifiers and plug in a USB dac or other.
Have you tried an inverter? A small pure sine inverter into the adapter or power supply that you plug into the tablet?
Not sure where you are grounding your amplifiers, but would it be possible to either ground the amps and power for the tablet at the same locations?
Another idea could be to use a bluetooth adapter and place that at the amps. I forget the high bitrate kind, but I know samsung uses that high quality codec over blutooth.
Another idea is if you use an apple tablet, you can stream to a device like the raspberry pi using shairport-sync. I use that in my home setup and it's dreamy. Place a Pi at your amplifiers and plug in a USB dac or other.
Hello,
sorry that I was off a bit, I was busy with work and some other stuff. The problem is the ripple (smaller ripple I can achieve to get, less the noise I get) I will try with LDO regulator.
I will post the resoults when I try it, but it will take some time, because I must solve some other stuff first.
Thank you
sorry that I was off a bit, I was busy with work and some other stuff. The problem is the ripple (smaller ripple I can achieve to get, less the noise I get) I will try with LDO regulator.
I will post the resoults when I try it, but it will take some time, because I must solve some other stuff first.
Thank you