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Ground Loop Isolator

Optimus Joe

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My factory cassette radio finally bit the dust, so I went and picked up a cheap aftermarket. Also installed an aftermarket USB plug where the cigarette lighter is next to the radio. I used Scosche Car Stereo connector to re-use the factory wiring to the new wiring. I also was able to use the cigarette lighter wiring for the USB plug. Now, when I use my iPod or phone to the radio on the Aux In line and attempt to charge the device at the same time, I get a terrible whirring/whining.

I looked into this and I can get a ground loop isolator for the aux plug, but am wondering if there is something I can do with the wiring for the USB plug instead of adding another set of plugs.

Thanks in advance.
 
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C420sailor

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Very strange. I plug my phone into a USB Charger (the power port on the lower right side of the console) and into the AUX input on my radio, no problems. Mine isn’t a hardwired USB port though—its a charger adapter.

Out of curiosity, who makes the head unit and the USB port? I’ve seen cheapo USB ports cause all sorts of RFI issues in airplanes.
 
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Gmctyphoon

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Try giving the new radio its own ground. Instead of using the black wire on the schosche harness.

Add wire if needed and a ring terminal and attach to bare metal.
 
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J_C

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You could try an LC filter on the USB charger power supply, or more commonly placed on the radio power supply, but to some extent they need selected to target the offending frequency of the noise which I can only guess is somewhere between 50KHz and 200KHz.

Does the new radio have the option of bluetooth input? That might be the easiest way to solve this, does use more power to transmit but if the device has charging power already, it's not an issue of running its battery down too fast.
 
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Optimus Joe

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You could try an LC filter on the USB charger power supply, or more commonly placed on the radio power supply, but to some extent they need selected to target the offending frequency of the noise which I can only guess is somewhere between 50KHz and 200KHz.

Does the new radio have the option of bluetooth input? That might be the easiest way to solve this, does use more power to transmit but if the device has charging power already, it's not an issue of running its battery down too fast.
It does have bluetooth and that seems to work ok. I was just hoping to use an old iPod instead of the USB drive since there is a 32gb limit and I have a 100+gb iPod that does not have bluetooth functionality.
 
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J_C

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^ 32GB is not a small amount of music! Heh, a couple of audio devices I use, just have some old flash card or USB drive that's 16GB and one 4GB. Guess it depends a bit on whether you use MP3 or uncompressed like FLAC.

Regardless, I would test their claim by trying a larger capacity drive. Sometimes they rate capacity based on lowest common denominator and true capacity can be higher, for example if you have a way to format > 32GB to FAT32, that might work, or it might understand exFAT filesystem.

Note that there is something about Windows OS, where if you try to format a drive above a certain size, even if FAT32 could support it, and you pick FAT32, it silently decides for you to format it to exFAT instead. I forget all the details, but there are ways around that like using a 3rd part format utility or a different OS that doesn't impose an artificial limit on FAT32 volume size. It could be that this doesn't work, but I wouldn't trust their claim of 32GB limit as I've had several devices in the past that supported higher than the limit the manufacturer claimed, was more about what filesystem it supported, AND media that is larger than 32GB may ship out already formatted to something other than the FAT32 that it "might" need.

 
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Optimus Joe

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Try giving the new radio its own ground. Instead of using the black wire on the schosche harness.

Add wire if needed and a ring terminal and attach to bare metal.
Tried this tonight and no dice. While the whirring was somewhat less it was still very noticeable.

Any other ideas?
 
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Gmctyphoon

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Try using the regular cig lighter and a USB adapter to charge the iPod. If no whine then it’s your new usb charger.
 
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Optimus Joe

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Try using the regular cig lighter and a USB adapter to charge the iPod. If no whine then it’s your new usb charger.
If it is the USB adapter, is there anything I can plug in or add on the USB ground to eliminate this?
 
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C420sailor

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Probably, but at that point I’d rather try another high quality USB supply or just go with the plug-in adapter. Doesn’t look as good, but mine is a cheapo and works 4.0. No sense in doing electrical engineering just to reinvent the wheel, IMO.
 
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Optimus Joe

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Well I tried it using a cigarette lighter USB charger and I got the same issue. So I opened it all back up ran a wire directly to the frame and to the battery and both still gave me the whirring sound. At this point I'm just going to not charge my iPod while also using it. Unless somebody else has a better idea cuz I'm open to them.
Thanks
 
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J_C

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Better is a subjective thing. There are things that can be done but it depends on what amount of effort and how much charging the iPod is worth to you.

I mentioned previously, a way to check whether it is a ground loop by connecting just the ground of the connector, or whether it is the buck regulator noise getting back into the system from the USB charger circuit, combined with the obviously low PSRR (power supply ripple rejection) of the new stereo.

For example, if your ipod goes into a low power mode where it doesn't power the screen, or maybe even if it does, the question is how much current it needs to stay level on battery, so at least it doesn't discharge even if it doesn't charge. The direction I'm going here is that you then wouldn't even need a switching buck supply for USB 5V, could just do it with a linear regulator which produces practically 0 noise, "if" it's the switching circuit causing noise instead of a ground loop.

If it's the switch circuit, a simple textbook LM7805 regulator circuit could supply power to maintain the same charge level, or a different 5V output buck switching PSU module.

If your current USB charger has a casing that allows opening it, it could even be as simple as switching the input capacitor to shift the noise frequency or magnitude.

The ease in doing any of this, depends on too many factors to consider remotely. I mean there's even the option of just sending the radio back if it can't reject the noise, get a refund and start over there, or just have a portable USB power bank that you charge every once in a while, to power the ipad, or what I already suggested, that you shouldn't really need 100GB of music as that is more than you could listen to on the longest of trips.

Suppose very high bitrate MP3, arguable an inaudible difference between it and lossless FLAC. That would make the average song about what? Just throwing a # out, lets say 10MB per song. With a 32GB limit (if there really is one, see my prior post), that is still over 3000 songs, and if you're on THAT long a trip, can't you just take a 2nd 32GB flash drive with you and swap it during the days to weeks it'd take to make it through that many songs?

It seems like you want to make it hard on yourself and I am willing to help you do that, lol.

The easy answer here is that if you want more than 32GB support, you get a stereo head unit with more than 32GB support. Tethering a host phone or tablet to do this then run a charger and cable too, is a fiddly hassle compared to the stereo head unit doing it all itself.
 
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Optimus Joe

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Better is a subjective thing. There are things that can be done but it depends on what amount of effort and how much charging the iPod is worth to you.

I mentioned previously, a way to check whether it is a ground loop by connecting just the ground of the connector, or whether it is the buck regulator noise getting back into the system from the USB charger circuit, combined with the obviously low PSRR (power supply ripple rejection) of the new stereo.

For example, if your ipod goes into a low power mode where it doesn't power the screen, or maybe even if it does, the question is how much current it needs to stay level on battery, so at least it doesn't discharge even if it doesn't charge. The direction I'm going here is that you then wouldn't even need a switching buck supply for USB 5V, could just do it with a linear regulator which produces practically 0 noise, "if" it's the switching circuit causing noise instead of a ground loop.

If it's the switch circuit, a simple textbook LM7805 regulator circuit could supply power to maintain the same charge level, or a different 5V output buck switching PSU module.

If your current USB charger has a casing that allows opening it, it could even be as simple as switching the input capacitor to shift the noise frequency or magnitude.

The ease in doing any of this, depends on too many factors to consider remotely. I mean there's even the option of just sending the radio back if it can't reject the noise, get a refund and start over there, or just have a portable USB power bank that you charge every once in a while, to power the ipad, or what I already suggested, that you shouldn't really need 100GB of music as that is more than you could listen to on the longest of trips.

Suppose very high bitrate MP3, arguable an inaudible difference between it and lossless FLAC. That would make the average song about what? Just throwing a # out, lets say 10MB per song. With a 32GB limit (if there really is one, see my prior post), that is still over 3000 songs, and if you're on THAT long a trip, can't you just take a 2nd 32GB flash drive with you and swap it during the days to weeks it'd take to make it through that many songs?

It seems like you want to make it hard on yourself and I am willing to help you do that, lol.

The easy answer here is that if you want more than 32GB support, you get a stereo head unit with more than 32GB support. Tethering a host phone or tablet to do this then run a charger and cable too, is a fiddly hassle compared to the stereo head unit doing it all itself.
Thanks for all the info.

I do not want to make it hard on myself, it was more of one of those things where I had something in mind and really wanted to make it work. I can as long as I am not charging while using the iPod. As far as Bluetooth goes, it works fine and honestly will probably wind up using that more than anything. I just liked the option of using an old iPod to keep with the older aesthetic I am going with the Explorer if that makes sense.

At this point, I am done messing with it and will probably use it as is for now. Especially now that my passenger door is acting weird and I need to mess with it. Will probably come back to it at some point.
 
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