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Old 18th March 2012, 01:42 AM   #1861
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OK I will check your suggestion now.

in the meantime, same test with a different 182P12 and GBPC102-E4/51 rectifiers this time.

EXACTLY the same results.

Further measurements show that the AC on the secondaries (bridge input) is 12,4V at all times.
What changes is the DC voltage on the output of the bridges.

I am also posting a photo of the circuit, in case you have any idea of something that could 've slip my mind. The transformer is wired for 230V operation. White and brown wires are soldered together to give primaries in series. The lower voltage on the output occurs when I feed the phase of the power line to the black(dotted) wire, and the normal when I feed it to the orange. Secondary dotted wires are red and grey.
I also tried with the fuse connected before the black wire. Same behaviour (11.5V when phase is on black).
The case is earthed through the IEC's metal body.
The board of the bridges is a goodish quality protoboard.

On the output side, blue is V-- (xlr pin 2), orange is V++ (xlr pin 1), brown and white are common center (xlr pin 3). No xlr pins are grounded (neutrik chassis socket).

Click the image to open in full size.

PS the case is too small for the transformer. I just use it for now to keep everything in place. I do not close it for the tests.
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Last edited by dimkasta; 18th March 2012 at 02:06 AM.
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Old 18th March 2012, 01:59 AM   #1862
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I measured the transformer.
Primaries in series are 12.2ohm.
Secondaries are 0.5 ohm each.

When I measure resistance between primary and secondaries I get absolutely no action. Like no connection is detected. Same between the two secondaries on all combinations of wires. Measured with 3 different DMMs.

I guess there is no problem with the transformers after all?
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Old 18th March 2012, 02:06 AM   #1863
kor952 is offline kor952  Netherlands
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Maybe a typo but you mention orange twice, first to serialize the primairy and second you connect the phase to it, should the second time be red?

Ronald.

EDIT: OK...Solved

Last edited by kor952; 18th March 2012 at 02:16 AM.
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Old 18th March 2012, 02:13 AM   #1864
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Sorry typo. Primary series connection is between brown and white. Corrected it
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Old 18th March 2012, 02:36 AM   #1865
kor952 is offline kor952  Netherlands
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The only thing I can make up is that there are different diode losses in the bridges. You could measure voltage between all pins of the bridges, both with the mains connected 'in phase' and 'out of phase'.

Ronald.
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Old 18th March 2012, 02:58 AM   #1866
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All diodes measure ~0,45V on the diode test of the DMM.

With the phase on the Orange cable, I got:
Between + and blue: 6,3V AC
Between + and red: 5,3V AC
Between - and red: 5,3V AC
Between - and blue: 6,3V AC

With the phase on the Black
Between + and blue: 5,6V AC
Between + and red: 6,4V AC
Between - and red: 6,4V AC
Between - and blue: 5,6V AC
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Old 18th March 2012, 03:38 AM   #1867
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OK... here is the output of the secondaries (while attached to the bridges). It s actually not symetrical... A problem in the power network?

Click the image to open in full size.

Perhaps it would be a better idea to use a higher voltage transformer and use 7812 and 7912 to get the proper voltages for V++ and V--?
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Last edited by dimkasta; 18th March 2012 at 03:48 AM.
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Old 18th March 2012, 03:46 AM   #1868
rjm is offline rjm  Japan
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I'm beginning to think it's all some measurement artifact. There does not seem to be anything wrong with your power supply.

I'd go ahead and attach to the VSPS and check the measurements again. It might that without filter caps and unloaded, the interaction with your meter/scope is causing strange effects.

Looking at your latest scope trace, and almost certain of it.
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Old 18th March 2012, 04:30 AM   #1869
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Giving power to either wire (black or orange) with VSPS attached, 15.7V on V++ and -15.7 on V-- (31.4 between them) and -8.8V between ground and pin 4 and 8.8V between ground and pin 7 of IC1.

It s a good thing the x-reg works evening things out

I probably messed up the capacitors' pads?

Last edited by dimkasta; 18th March 2012 at 04:48 AM.
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Old 18th March 2012, 06:13 AM   #1870
rjm is offline rjm  Japan
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So in other words, it's working fine?
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