I just built an amp and after burning up several phones and ipods, I learned something. The ground planes on both the phones and amps are shared by the power input and the audio input/output, it's very important that the grounds be taken from a common point. This was my first failure. Then after several hours of successful testing I unplugged the amp and plugged it back in, and just like that, POP, killed another Ipod.
I finally see what's happening Using the barrel plug that comes on the amp, when you start to plug it in, the center, positive terminal, connects first, then the ground connects. For that split second, where only the hit wire is connected, the amp pulls its ground from the audio cable instead, meaning the phone ground gets 24v across the power ground and audio ground for a split second. Long enough to fry an ipod. I could simply remember to disconnect the ipod before the amp but this isn't a very good solution since if one were to forget or if a wire inadvertently came detached, you'd fry your device. What is the solution to this? Is there some way to isolate the grounds so that they are not shared?
I finally see what's happening Using the barrel plug that comes on the amp, when you start to plug it in, the center, positive terminal, connects first, then the ground connects. For that split second, where only the hit wire is connected, the amp pulls its ground from the audio cable instead, meaning the phone ground gets 24v across the power ground and audio ground for a split second. Long enough to fry an ipod. I could simply remember to disconnect the ipod before the amp but this isn't a very good solution since if one were to forget or if a wire inadvertently came detached, you'd fry your device. What is the solution to this? Is there some way to isolate the grounds so that they are not shared?
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Here's my schematic.
You can see if I somehow lost the ground between the amp and the battery, the full current would be pulled through the ground plane of the phone. This is what's happening when I connect the barrel plug and the positive connection is made first. Full current of the amp through the IPOD and POOF, magic smoke comes out of IPOD.
You can see if I somehow lost the ground between the amp and the battery, the full current would be pulled through the ground plane of the phone. This is what's happening when I connect the barrel plug and the positive connection is made first. Full current of the amp through the IPOD and POOF, magic smoke comes out of IPOD.
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Even if I turn off the amp there is a lot of inrush current as evidenced by the spark that is thrown when connecting the barrel plug. I fear this inrush current could be enough to damage the phone.
Would a simple ground loop isolator break the ground? I'm not exactly sure how those work.
Ground loop isolator
Ground loop isolator
Well... you could switch the polarity on the barrel plug so ground connects first. Be sure you reverse it going to the circuits too.
opto-isolator vs transformer ground loop isolators. Any preference?
So after reading more about ground loop isolators, this appears to be exactly what I need.
Ground Loop Isolators
The question is whether a opto-isolator or transformer would work better.
Opto-isolator
The transformer based isolator will block DC but the opto-isolators are unidirectional and they cannot transmit power.
Anybody have a preference?
So after reading more about ground loop isolators, this appears to be exactly what I need.
Ground Loop Isolators
The question is whether a opto-isolator or transformer would work better.
Opto-isolator
The transformer based isolator will block DC but the opto-isolators are unidirectional and they cannot transmit power.
Anybody have a preference?
All grounds are now to the same point. But that doesn't help when using the barrel plug on the amp. I tested a ground loop isolator and it does indeed break the ground between the two devices so I think it will work. It works through induction, only when there is current between the ground and the Right or Left audio wire. If there is current on the ground only, nothing will be induced, plus it's DC and the transformer can't pass DC current. I'll update my schematic for anyone that is interested.
That would be one way to do it. Do you think the ground loop isolator will still give me issues?
It's one of those little 12v cigarette lighter to 5v usb adapters for charging devices. It's actually most likely a 7805 5v voltage regulator (hence the shared ground), not a transformer, but I didn't know how to draw that, lol.
7805, no. It is a switching regulator inside, but non isolated.
Even if you use batteries for the supply, the load should have bypass capacitor(s) closely installed.
I doubt there is any ground loop issue with such less connections. I feel more of, that you are ignoring some practice(s) like connecting shield on both ends (is a NO).
Gajanan Phadte
Even if you use batteries for the supply, the load should have bypass capacitor(s) closely installed.
I doubt there is any ground loop issue with such less connections. I feel more of, that you are ignoring some practice(s) like connecting shield on both ends (is a NO).
Gajanan Phadte
"you are ignoring some practice" This very well may be. I know just enough to be dangerous. I appreciate your help though so that this doesn't happen again. It was frustrating.
I know the 7805 is non-isolating. That's why I connected the ground in the diagram.
This is the amp I'm using: Finished TPA3116 2 1 50W 50W 100W Class D Amp Amplifier Board | eBay
Which shield are you talking about? None of the wires I use have a shield.
Would you still need bypass caps installed or would you assume they are built in? I was under the impression that you could plug in power, speakers, and an audio source and be done with it.
As for the ground loop, I agree that there is no ground loop. There is no humming and the audio is clean while playing. However, the ground loop isolator was a simple way of breaking the continuity of the ground to prevent inadvertent DC current from flowing through the ground plane of the phone. This only happens if you loose your ground on the amplifier for some reason. This device goes in an ice chest and is going to float down the river with me so there is a chance that with all the movement, no matter how good the connections are, one may come disconnected and I don't want to risk that blowing up an IPOD or phone. Also because of the design of the barrel plug, you momentarily loose ground. I don't want to rely on the barrel plug staying engaged.
I know the 7805 is non-isolating. That's why I connected the ground in the diagram.
This is the amp I'm using: Finished TPA3116 2 1 50W 50W 100W Class D Amp Amplifier Board | eBay
Which shield are you talking about? None of the wires I use have a shield.
Would you still need bypass caps installed or would you assume they are built in? I was under the impression that you could plug in power, speakers, and an audio source and be done with it.
As for the ground loop, I agree that there is no ground loop. There is no humming and the audio is clean while playing. However, the ground loop isolator was a simple way of breaking the continuity of the ground to prevent inadvertent DC current from flowing through the ground plane of the phone. This only happens if you loose your ground on the amplifier for some reason. This device goes in an ice chest and is going to float down the river with me so there is a chance that with all the movement, no matter how good the connections are, one may come disconnected and I don't want to risk that blowing up an IPOD or phone. Also because of the design of the barrel plug, you momentarily loose ground. I don't want to rely on the barrel plug staying engaged.
The one you are looking at is not only a LCD display, but is a module with its integral drive and cannot be used with 7106.
What you need is a plain 3 and half digit SEVEN SEGMENT LCD display with sign.
Gajanan Phadte
What you need is a plain 3 and half digit SEVEN SEGMENT LCD display with sign.
Gajanan Phadte
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