Chip Amp PSU Question

[Lyerigolfin]

I've assembled the power supply in this thread:
The (high-cap.) unregulated PSU for chipamps

also the same (basic) design can be found here:
http://www.tnt-audio.com/clinica/ssps1_e.html

and here:
www.zero-distortion.com (ps design section)

My question is about the 0v line. I actually measured this line compared to the earth ground and there was about a 32V-P sine wave showing up. The positive and negative rails displayed proper values when compared to the 0v line.

All of the power supply schematics that I've seen show this 0v rail tied to earth. Last time I checked a 32V sine wave shorted to earth would make quite a few (rather expensive) things blow up.

I could see maybe, if you used two transformers with series windings and tied each of their centers to the 0v point, but is this kind of power supply design possible with only 1 transformer?

[officeboy]

This is one of those times when a picture is worth a 1000 words.

Or if a picture is not available, a drawing of the exact items used and how they are hooked up (a schematic, but not a copy of one from the links you posted),.

Also there is a power supply forum that is fairly active and would be able to provide you with some answers.

[leadbelly]

If I understand you correctly, you have built the PS per the schematic with the exception that you did not tie one output of each bridge to ground. This is the line labelled as GND in the carlosfm schematic and you are calling the "0V" line (BTW, it can't be 0V if it's not grounded )

If you have indeed done this and you have no galvanic connection to ground anywhere in your PS circuit on the secondary side of the transformers, then there is nothing wrong. Of course you will read an unusual value like 32V on the "0V", there is nothing in your circuit to reference it to ground.

[Lyerigolfin]

First off I apologize for not posting this in the PS design forum, I didn't know about it when I created the thread.

Secondly, you are correct. I have assembled the supply with jumper wires and alligator leads without connecting the 0v reference line to ground. To be safe, I decided to measure the voltage from this line to ground before hooking it up, when I did I found the aforementioned voltage. Why exactly will this not just cause a massive failure/fire/catastrophe when shorting this 32V AC to ground? I fail to see how (massive) current wouldn't flow between 32V AC and earth ground.

[Lyerigolfin]

Here's an attached picture of the exact layout that I've built.

[leadbelly]

Originally posted by Lyerigolfin
Why exactly will this not just cause a massive failure/fire/catastrophe when shorting this 32V AC to ground? I fail to see how (massive) current wouldn't flow between 32V AC and earth ground.

Well, what can I say other than read up on some theory? Since you are sitting there at a standstill because you won't take my word for it, at least try shorting "0V" to ground with a fuse so you can move forward and build your amp

[paulb]

Originally posted by Lyerigolfin
Why exactly will this not just cause a massive failure/fire/catastrophe when shorting this 32V AC to ground? I fail to see how (massive) current wouldn't flow between 32V AC and earth ground.

You're getting some leakage through various things. It will be a high impedance source. Try connecting a 1K (or whatever) ohm resistor across your meter and then measure the voltage. If it doesn't drop to a very low value, then you've got some serious problem.

[Lyerigolfin]

Originally posted by leadbelly


Well, what can I say other than read up on some theory? Since you are sitting there at a standstill because you won't take my word for it, at least try shorting "0V" to ground with a fuse so you can move forward and build your amp

I do plan on taking your word, and everybody elses word for that matter. My workspace is at my uncle's house which I don't go to very often so I don't get to work on it a lot (meaning I sit around and think about it a lot).

The high impedance source makes sense to me. I'll take some current measurements as well as voltage measurements from this return line. I also now realize where the 60hz hum comes from in ground loops, I never found a fully technical enough answer outside of "don't ground this here, because it will form a loop" to completely understand it. I always understood the physical resistance property, but I never knew why it would hum at 60hz.

Thanks for the help.

[officeboy]

Just to chip in since I did earlier. Leadbelly is right, you just need a reference point to tie that ground back to. Unless you have a failed transformer or other component.