Problem from a newbie...
I wanted to build a simple power supply for my monica dac and house it all together in one box.
I bought a traffo with 12VAC output, 250mA, bridge rectifier and a 7812 fixed voltage regulator.
I hook it up and I get 12VAC from the traffo secondary. I connect up to the rectifier and I get about 10VDC from the rectifier, and then about 8VDC from the regulator. If I put a MM across the rectifer + and - outputs, I get the above mentioned 10VDC, but if I switch the MM to measure AC, I get about 4 to 5VAC steady on the MM. If I hook it all up to the DAC, the DAC will lock on, give me music but also a whopping great hum, which I think must be from the AC.
So I thought it must be the rectifier, I replaced this with a new one, but still the same. Same with the regulator.
I recently built a similar PSU for a phono stage (only with + and - VDC output) and it worked out fine. What am I doing wrong? Seems like the transformer is the only thing different. On the phono stage, the VDC after rectifier is up at 17VDC from a 12V secondary. Is the traffo too small?
Oh, I know the DAC is OK, because I tried it out with a different PSU and it works AOK.
thanks for any help,
Fran
I wanted to build a simple power supply for my monica dac and house it all together in one box.
I bought a traffo with 12VAC output, 250mA, bridge rectifier and a 7812 fixed voltage regulator.
I hook it up and I get 12VAC from the traffo secondary. I connect up to the rectifier and I get about 10VDC from the rectifier, and then about 8VDC from the regulator. If I put a MM across the rectifer + and - outputs, I get the above mentioned 10VDC, but if I switch the MM to measure AC, I get about 4 to 5VAC steady on the MM. If I hook it all up to the DAC, the DAC will lock on, give me music but also a whopping great hum, which I think must be from the AC.
So I thought it must be the rectifier, I replaced this with a new one, but still the same. Same with the regulator.
I recently built a similar PSU for a phono stage (only with + and - VDC output) and it worked out fine. What am I doing wrong? Seems like the transformer is the only thing different. On the phono stage, the VDC after rectifier is up at 17VDC from a 12V secondary. Is the traffo too small?
Oh, I know the DAC is OK, because I tried it out with a different PSU and it works AOK.
thanks for any help,
Fran
God this is going to sound stupid, but I don't have a cap in there yet.....
Thats whats wrong, isn't it? The caps are on a separate board on the phono stage.
God I feel stupid now!
OK, so that would be a helping of humble pie, with cream please!
When you have stopped laughing, what size caps would you reccomend? I have some 3300uF to hand, also 470uf and 100uf - all polar electrolytics.
red with embarrasment (though I did say I was a beginner!),
Fran
Thats whats wrong, isn't it? The caps are on a separate board on the phono stage.
God I feel stupid now!
OK, so that would be a helping of humble pie, with cream please!
When you have stopped laughing, what size caps would you reccomend? I have some 3300uF to hand, also 470uf and 100uf - all polar electrolytics.
red with embarrasment (though I did say I was a beginner!),
Fran
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