Eliminate power noise in hacked CD player project

[Jezzaaaa]

Hi all

I have an old mains-powered CD player where the CD doesn't work anymore, and the antenna has snapped off, so not much use for radio. (Although I could go replace the antenna, nobody uses radio anymore anyway.) This device also has an iPhone/iPod mounting point with a 30-pin connector to power and interface to the iDevice.

To breathe new life into the player, I bought a wifi-connected media device (Tronsmart M1000 EzCast) that has an audio out socket, and I wired it into the iPod plug audio input lines using the cable from a busted set of headphones. The cable feeds through a hole into the CD tray area in the top, and plugs into the audio out of the M1000. The M1000 device is small enough that I can pop it in where a CD would normally go, and close the lid. Neat!

Surprisingly, it works great. I know a little about electronics in principle, an I kind-of know about passive components, transistors and ICs, but only as idealistic building blocks. And I have next-to-no experience with real-world projects like this one. So I was surprised how well it worked.

Now the M1000 has no battery, and instead has a USB socket for power. So I have to use a USB power pack and run the 5v power line past a crack in the lid of the CD player to power the device. This is not only untidy, but it also means I need two mains power sockets to run the thing. It would also be nice to be able to use the CD player in this configuration when it's running on batteries, and hence fully portable.

So I decided to get an old USB power cable with a busted PC end plug, and do the same as for the audio - wire it into the iPod connector and feed it through a hole into the CD tray area for powering the device. This works fine to charge it (and I can charge phones this way also). But when I'm playing audio at the same time as powering the device from the CD player, the audio has lots of noise, and it's simply unusable for music. If I unplug the audio cable, the noise (and the music) stops.

Has this something to do with a "ground loop" that I've read about (but admit to knowing nothing of)? Or is it some kind of interference induced into the audio cable through the M1000 device?

Can this be cured with a capacitor at the right place or some similar elector-magic?

 

[Gryd3]

Hi all

I have an old mains-powered CD player where the CD doesn't work anymore, and the antenna has snapped off, so not much use for radio. (Although I could go replace the antenna, nobody uses radio anymore anyway.) This device also has an iPhone/iPod mounting point with a 30-pin connector to power and interface to the iDevice.

To breathe new life into the player, I bought a wifi-connected media device (Tronsmart M1000 EzCast) that has an audio out socket, and I wired it into the iPod plug audio input lines using the cable from a busted set of headphones. The cable feeds through a hole into the CD tray area in the top, and plugs into the audio out of the M1000. The M1000 device is small enough that I can pop it in where a CD would normally go, and close the lid. Neat!

Surprisingly, it works great. I know a little about electronics in principle, an I kind-of know about passive components, transistors and ICs, but only as idealistic building blocks. And I have next-to-no experience with real-world projects like this one. So I was surprised how well it worked.

Now the M1000 has no battery, and instead has a USB socket for power. So I have to use a USB power pack and run the 5v power line past a crack in the lid of the CD player to power the device. This is not only untidy, but it also means I need two mains power sockets to run the thing. It would also be nice to be able to use the CD player in this configuration when it's running on batteries, and hence fully portable.

So I decided to get an old USB power cable with a busted PC end plug, and do the same as for the audio - wire it into the iPod connector and feed it through a hole into the CD tray area for powering the device. This works fine to charge it (and I can charge phones this way also). But when I'm playing audio at the same time as powering the device from the CD player, the audio has lots of noise, and it's simply unusable for music. If I unplug the audio cable, the noise (and the music) stops.

Has this something to do with a "ground loop" that I've read about (but admit to knowing nothing of)? Or is it some kind of interference induced into the audio cable through the M1000 device?

Can this be cured with a capacitor at the right place or some similar elector-magic?

For knowing so little, you've come prepared and have done your own research ahead of time.
I thank you for that first and foremost! Good job!

As far as the noise is considered, it's often picked up a couple different ways.
If there is current flow in the audio cable you may be hearing noise. This is particularly noticeable with dirty/noisy power. You *may* be able to clean this up by placing a capacitor in parallel to the device. This will help the higher frequencies (noise) on the power line to bypass the device/audio cable through the capacitor and will also allow the capacitor to smooth out ripple on the power line... You can also use an inductor in series with your device which will block high frequency noise, and smooth out the current passing through... The inductor solution may not be ideal if your device pulls varying amounts of current... these things are designed to oppose any changes in current. You may also use an 'inductive choke' . You often see these as those little blocks or cylinders on laptop power cables.
In short... you need very clean power, but to fix it properly you should break the loop. You can do this with an audio transformer placed in-line with the audio cable. This will eliminate the path for current flow down the audio line.

However... again (with a dirty power supply) if you audio cable is picking up noise simply by being near-by, then you need to reposition the power/audio cables. If you can help it, avoid running power and signal wires parallel to each other or they will pick up noise from each other. If you can't reposition the wires, the only other option is to clean the power supply using components like capacitors, inductive chokes, or inductors... best of luck!

If you can, a picture of the setup may help