[mikaelmark]

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. Is´nt 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.
 
http://www.ebay.com/itm/WM8741-DAC-DIR9001-CS8421-Coaxial-Optical-gz-2-/190649692643?pt=US_Home_Audio_Amplifiers_Preamps&hash=item2c639b71e3
 
 
Regards Mikael

 

[Lenni]

Hi, I think you'd get better answers in the DIY forum, or possibly even the Science forum.
 
maybe ask a Mod if they'd move it there..

 

[mikaelmark]

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, should´nt 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 it´s 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 could´nt 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