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Old 15th July 2012, 02:36 PM   #1
mikaelmark is offline mikaelmark
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Join Date: Jul 2012
Default Overheated DAC from eBay

I have recently bought a ready-built DAC with WM8741 and CS8421 uppsampling from eBay, and gave about $ 100USD. What was missing was an transformer; 2 * 15 volts and 2 * 9 Volt and a box to build it in.

I thought at first that I could fix my own toroidal transformer where I found the correct voltages from winding. Tested through with several transformers, but what happened was that the four rectifier diodes BYV27 to 9 Voltage was so hot that it began to smoke and I had to replace a couple of them with new ones. It is also heard a buzzing sound from the transformer.

But the DAC one does work, so I get sound from it when it is connected.

I have now got a recommended R-Core transformer. However, there was no difference, the same thing happened.

What I found when I looked at the card, was that the negative side of rectifier diodes for 9 Volt was connected to ground, which was not the case of 15 Volt. The negative side only connected to capacitors, but not directly to ground.

I tried then to cut the lead of the 9 volts to ground, and now did not diodes get so hot. However, I get no sound now, even though the LEDs are lit and all the ICs have power.

Only when I connect the cutted line to ground, I get sound while the rectifier diodes get hot and the transformer starts to growl.

Can the DAC card to be nonfunctional, or have I possibly done something wrong when I connect the transformer? Have connected all four cables from the 0 Volt cables at the transformer to 0 volts on the card, and each for 15, 15, 9, 9 Volt. That is, I have have taken a cable from each power and pairing them together to get 0 volts. Isīnt this the right way? I tried first to connect only 15 Volts 0 Volts cables, but that did not get 9 Volt to work on the board.

Regards Mikael
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File Type: jpg WM8741 DAC.jpg (52.2 KB, 177 views)
File Type: jpg R-Core transformator.jpg (46.3 KB, 175 views)
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Old 15th July 2012, 02:54 PM   #2
qusp is offline qusp  Australia
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Location: Brisbane, Australia
no, you are connecting it incorrectly. for 14-0-14 you need to use

so standing behind the tranformer with it between you and the dac board, you should connect the left yellow to 14 (this will become the negative phase wire, or beginning as its AC) then connect the right yellow and the left brown wire together at 0 and the right brown wire to the right side 14. with the 9v input just connect the left blue to the left side and the right blue wire to the right side

the 14-0-14 supply is a bipolar supply, it was correctly wired, only you connected the transformer wrong. did I read you say you were trying to wind your own transformers before this one? if so, cease trying to make transformers until you know how they work

Last edited by qusp; 15th July 2012 at 03:01 PM.
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Old 16th July 2012, 06:26 PM   #3
mikaelmark is offline mikaelmark
diyAudio Member
Join Date: Jul 2012
Thank you so very much for your reply!
The DAC is now up and running very nicely after I get a tip to disconnect the 0 Volt wires from the transfomer and connect both side from one linding, negative and positive phase AC! But what I think, shouldīnt the board be labelled: 14 - 0 14, 0 - 8, beacause the 9 Volt from the transformer is only using one linding with positive and negative phase AC, and not two 9 Volt, as itīs for the 15 Volt? I have even get a lot of help from an old guy at my work, who is an electrical engeineer and are building testing equipment, but he couldīnt get me the right answer about this!

Now I gonna swtitch the opamp OP215 to something nice, maybe a THS4032 I realy love this one, and have impemented it in several equipmints with good result)

Best regards: Mikael
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Old 16th July 2012, 11:06 PM   #4
AudioSan is offline AudioSan  Norway
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Join Date: Feb 2009
right conection is:
outher yellow 14V...inner yellow and inner brown together to form 0V... outher brown 14V (14-0-14V)
the 2 blue form the 9V. or the 2 white. (0-9V)
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