# EMF Oppsition in Adjacent Wires +/- Swing

## Main Question or Discussion Point

I have a straight piece of two conductor "figure eight" wire (like speaker wire or US power cord) laid out left to right.

I connect the output from a push-pull type audio amplifier across each conductor, but with the active and ground reference wires on opposite ends for each. Let's assume series resistance so no dead short.

As I understand, at any given moment (apart from crossover) the current in each conductor will be moving oppositely to the other, thus causing their respective EMF's to oppose.

My question relates to the fact that the push-pull output swings both plus and minus relative to ground.

1. Does this current reversal cause the EMF to oppose twice each cycle?

2. If so, is there any way to prevent this, e.g. with a blocking capacitor or isolation transformer? Please explain how in practical use.

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berkeman
Mentor

I have a straight piece of two conductor "figure eight" wire (like speaker wire or US power cord) laid out left to right.

I connect the output from a push-pull type audio amplifier across each conductor, but with the active and ground reference wires on opposite ends for each. Let's assume series resistance so no dead short.

As I understand, at any given moment (apart from crossover) the current in each conductor will be moving oppositely to the other, thus causing their respective EMF's to oppose.

My question relates to the fact that the push-pull output swings both plus and minus relative to ground.

1. Does this current reversal cause the EMF to oppose twice each cycle?

2. If so, is there any way to prevent this, e.g. with a blocking capacitor or isolation transformer? Please explain how in practical use.
Without a sketch or schematic, I could only guess at your question. Could you please sketch the circuit on paper and post a (clear, bright) cellphone picture using the UPLOAD button in the Edit window? You can Upload PDF or JPEG copies of the picture.

Also, the output of a push-pull amplifier can only swing negative if its power supplies include positive and negative rails (or if the output is capacitively coupled).

I have prepared a diagram but don't see any way to upload local content.

berkeman
Mentor
I have prepared a diagram but don't see any way to upload local content.
using the UPLOAD button in the Edit window? You can Upload PDF or JPEG copies of the picture.

If you mean the icons in the gray bar at the top of the text entry window, I find nothing that reads "upload". I can add an image but it then asks for its URL. My apologies for the handholding exercise, but I use a computer regularly and see no direct upload.

From another source, this is the type of situation referred to in my OP. Please reread for clarity. https://i.ytimg.com/vi/Mrr3wIFjxqI/hqdefault.jpg

The amp I have in mind is definitely push-pull output. A hi-fi unit with one channel to be connected across each of the + and - terminations as shown on the diagram linked above.

sophiecentaur
Gold Member
I use a computer regularly and see no direct upload.
I am. at this moment, looking at the Upload button on my browser. It is near the bottom of this message window and to the right of the Post Reply and Preview buttons. It will give you a file selection window etc. etc. follow the instructions it gives you.

I have great sympathy. Whenever I ask supermarket staff where an item can be found, I always find I am standing right next to it. Sheepish grin

If I could upload a screenshot, it would show there is nothing to the right of the post reply button. It's on the very edge of the content box. No "preview" button either. At a loss to explain, but then I use Linux.

Can anyone offer a reply to my original question?

Hmm. now the buttons have appeared in the "Have something to add?" field. IOW I needed to reply to myself (apparently).

So here is the diagram I made to clarify my original question.

#### Attachments

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sophiecentaur
Gold Member
If I could upload a screenshot, it would show there is nothing to the right of the post reply button. It's on the very edge of the content box. No "preview" button either. At a loss to explain, but then I use Linux.

Can anyone offer a reply to my original question?
This seems to me to be a question involving Inductance. Your arrangement has two loops in the opposite sense so the Inductance will be (ideally) zero for the reason you suggest. So called Bifilar windings are used when the parasitic (unwanted) Inductance needs to be eliminated or reduced. It works as long as the dimensions of the coil are a lot less than the wavelength of the signal.
PS Could the missing buttons have been caused by 'Zoom"? What actual browser are you using? Firefox works on most Operating Systems, I think.

berkeman
Mentor
1. Does this current reversal cause the EMF to oppose twice each cycle?

2. If so, is there any way to prevent this, e.g. with a blocking capacitor or isolation transformer? Please explain how in practical use.
If you drive the two wires in differential mode, then yes, you will get two opposite voltage peaks per AC cycle. If you drive them in common-mode, they have the same voltage throughout the AC cycle.

Can you say more about your project? We can probably help you figure out how to do what you want to do if we know more context. Thanks.