How do I ground this?

[saurus]

Please help! I have added an output buffer to a DAC that I built, and I can't figure out how to ground the thing. Here is what I have:

The 16vac from a single secondary (two wires) is split, with the first split going to the DAC's single-sided power supply (+5vdc/gnd). The signal and shield ground from the digital input RCA jack goes to the DAC board.

The second AC split goes to the buffer's dual power supply (+15vdc/0/-15). The signal from the DAC's analog output goes to the buffer input, but not the signal ground. The signal and ground to the analog output RCA jacks comes from the buffer board.

There is currently no direct connection between the DAC circuit and the buffer circuit, except for the AC in and the signal trace. I tried connecting the 0v center lead from the buffer's dual supply to the ground of the DAC's single supply, but that promptly blew the fuse. Now the thing puts out only a terrific 60(?) Hz hum.

What is the common connection between the two circuits, or is there one? How do I handle the grounding for this?

Thanks for any help you can give.

[lucpes]

Originally posted by saurus
Please help! I have added an output buffer to a DAC that I built, and I can't figure out how to ground the thing. Here is what I have:

The 16vac from a single secondary (two wires) is split, with the first split going to the DAC's single-sided power supply (+5vdc/gnd). The signal and shield ground from the digital input RCA jack goes to the DAC board.

The second AC split goes to the buffer's dual power supply (+15vdc/0/-15). The signal from the DAC's analog output goes to the buffer input, but not the signal ground. The signal and ground to the analog output RCA jacks comes from the buffer board.

It is best to use complete separate power supplies in this case (or at least two secondaries). At this size another trafo won't kill your wallet so go for that!. In theory the sound quality should be better so the only drawback is the small added cost.

I had similar troubles when building two 'simple' PS's using 7815 & 7915s for a 'dual channel' preamp and the only sollution was to buy another small toroid.

[saurus]

Thanks for the advice. I will get another transformer if I must, but is this really the only way? Since both power supplies are drawing from the same AC secondary, is there no common ground between the two circuits?

[janneman]

Can you draw a circuit? How are the diode (bridges) connected? This IS a power supply, or what?

Jan Didden

[saurus]

Thanks - Here is a schematic of sorts showing what I have:

[Jax]

Short term solution: remove B1 and connect the IN of the 5V regulator to IN of the +15V. Connect the grounds of all regulators together.

Long term: use another transformer for the 5V supply.