living sounds
Well-known member
I'm wondering about the best way to approach groundingin the following 2-channel DAC scenario:
Switch-mode PSU +/-15VDC powers everything:
- powers directly (with added LCR filters) analog buffer/balancing output board (2 NE5532 in inverting configuration drive XLR outputs, pin 1 is only connected to chassis)
- powers DAC board via an additional linear PSU that puts out +/-7VDC, DAC board again has additional regulators on board to create +3.3VDC for digital and +/-4VDC for resistor ladder; AES/EBU digital input connection is transformer balanced with ground either floating or shield connected to chassis at pin 1 entry
- both DAC board and analog output board have thick PSU ground connections going to the linear PSUs output ground (DAC board) and the +/-15VDC ground (analog buffer board), these PSU grounds are closely connected via low impedance lines
- chassis ground is currently only connected to the board grounds at the point after the +/-VDC switch mode PSU (bolted down directly below the PSU)
- the unbalanced analog output of the DAC board goes to the buffer/balancing board via two microphone cables, the shield joins the DAC boards analog output ground to the buffer board ground
Please see my truly awful (MSPaint) drawing attached. It shows only the relevant grounding.
Here's the problem:
The DAC boards analog ground and the buffer boards audio ground should be connected directly to allow signal flow between the two; otherwise, with grounds connected through the PSU return lines, the return paths cross through dirty PSU ground;
But, the direct connection between the DAC board and the balancing board (with violet spray around in the drawing) also produces a ground loop and potential undesireable return paths for PSU decoupling signals.
There's no measureable increase in hum with the grounds connected, but the low end sounds better without the connection.
Would it make any sense to join the two audio grounds just with a small cap? Or is there another way to optimize things here?
Thanks!
Switch-mode PSU +/-15VDC powers everything:
- powers directly (with added LCR filters) analog buffer/balancing output board (2 NE5532 in inverting configuration drive XLR outputs, pin 1 is only connected to chassis)
- powers DAC board via an additional linear PSU that puts out +/-7VDC, DAC board again has additional regulators on board to create +3.3VDC for digital and +/-4VDC for resistor ladder; AES/EBU digital input connection is transformer balanced with ground either floating or shield connected to chassis at pin 1 entry
- both DAC board and analog output board have thick PSU ground connections going to the linear PSUs output ground (DAC board) and the +/-15VDC ground (analog buffer board), these PSU grounds are closely connected via low impedance lines
- chassis ground is currently only connected to the board grounds at the point after the +/-VDC switch mode PSU (bolted down directly below the PSU)
- the unbalanced analog output of the DAC board goes to the buffer/balancing board via two microphone cables, the shield joins the DAC boards analog output ground to the buffer board ground
Please see my truly awful (MSPaint) drawing attached. It shows only the relevant grounding.
Here's the problem:
The DAC boards analog ground and the buffer boards audio ground should be connected directly to allow signal flow between the two; otherwise, with grounds connected through the PSU return lines, the return paths cross through dirty PSU ground;
But, the direct connection between the DAC board and the balancing board (with violet spray around in the drawing) also produces a ground loop and potential undesireable return paths for PSU decoupling signals.
There's no measureable increase in hum with the grounds connected, but the low end sounds better without the connection.
Would it make any sense to join the two audio grounds just with a small cap? Or is there another way to optimize things here?
Thanks!