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How can I eliminate the electric potential difference between my power supply's negative and ground? Answered

Hello everyone!
The question is pretty straight forward, I have my fair share with electronics, so I'm not really new.
I have a linear power supply in my shop and only now it has started bothering me that there is like 35V between my psu's negative and ground.
I would normally not care, but since I've gotten into audio and video I found it to be problematic, because every time I connect my psu's negative to my lets say source audios' negative, 4 amps start to flow from my amp to ground trough the thin audio cable I use. I know it's not my source's fault because it's switching psu's negative is shorted to ground.

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3 years ago

I was going to mention that it is probably because of a low side current sense resistor, but looking at the schematic you posted and you mentioning that there is a 35V difference, there is something else going on. It appears that, other than the "ground" connection on the supply negative, the whole linear regulator circuit is floating. So the negative of your power supply is, according to the schematic, defined as ground. It *is* the ground. Most likely a chassis and earth ground.

So I honestly think the problem is that your audio source negative being referenced to a negative supply voltage, which is very strange indeed. I would investigate the circuitry for that. Ground loops can be mysterious because we use "ground" as a common point and expect it to always be the same potential, but in real life that is not always the case.

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iceng
iceng

Answer 3 years ago

+1

Good reasoning advice.

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iceng
iceng

3 years ago

Four terminal power supplies have two
small sensor extra leads that measure the voltage at the point where the
power wires deliver the energy to a load...

Your situation may have a ground loop heavy current...

I would;

1] Join the negative and chassis ground at one just one single point.

2] Try to discover the recommendations by the manufacturer.

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R4MP4G3RXD
R4MP4G3RXD

Answer 3 years ago

The variable linear psu I'm using is home made and was made by my dad back in the day. Here is it's schematic:
I can't connect the psus' negative to ground because of the 4 amps I was talking about.

img039.jpg
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Answer 3 years ago

The negitive of that linear power supply is referenced to ground. I think there is something else going on.

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Jack A Lopez
Jack A Lopez

3 years ago

What is this node you call "ground" ? Do you mean the ground wire of the mains power? Perhaps the power supply has a metal case, and this metal case is connected to the mains power ground, and also connected to one of the output rails of the supply?

I suggest looking into the body of this power supply, for to discover the place where it is connected to this "ground". Then disconnect that connection, if possible.