Grounding strategy?

[Pars]

I'm modding an Adcom CD player for a member here, installing a pair of Colin's I/V boards (player is balanced), and am debating on how and where to connect ground on these to the main board and power. These boards have on-board shunt regulators, so I am tapping power from the main filter caps right after the rectifiers for the 2 +/-15V power supplies for the analog section on the main board. AFAIK, it is usually not a good idea to connect more than 1 ground per board. The options I see are:

1. Ground the boards through the power connector
   
2. Ground the input of the boards
   
3. Ground the output of the boards
   

Currently, I am leaning towards #1, thinking that noise from the shunt regs, etc. should feed back to the ground plane near the PSU instead of being dumped into the ground plane near the DACs. Ground plane seems to be common between the sections. The one that Colin did (same player) used #2.

The stock analog stage is completely depopulated, other than the muting relays. From the schematics, it does not appear that anything else uses the +/-15V supplies.

Thanks for any thoughts.

[luvdunhill]

#1 is my vote

[dsavitsk]

1 as well, but it surely doesn't matter here. Since it is balanced, any induced ground noise will be cancelled. And, the preamp this is feeding has input transformers, and the circuit is truly differential and has no ground reference. What matters more is keeping the offset between the + and - pins to absolutely 0. Even a mV will interfere with the amorphous cores.

[Pars]

The player has both single ended and balanced outputs, so both need to work. Output jacks will remain wired to the main board.

So with his preamp (I presume you know who this is for), the two halves of the I/V stage boards (+ and - signals per) need to be within a mV of each other? Hmmm, didn't know what I was signing up for here May not be a problem as they seem rather close just checking individual offsets to ground, but that is on the bench and just each individual board.

[dsavitsk]

So with his preamp (I presume you know who this is for),

Indeed.

the two halves of the I/V stage boards (+ and - signals per) need to be within a mV of each other?

As close as you can. Each board has a servo that should keep the output very close to ground. In a pinch, the servo opamps can have their offset trimmed, so you can solder in a trimmer across two of the pins (I think Colin left them unused) to zero this out. It probably won't be necessary. But, the transformers really do not like any offset.

[luvdunhill]

interesting article:

http://www.diyaudio.com/forums/diyaudio-com-articles/163575-audio-component-grounding-interconnection.html

[recstar24]

So basically you are saying singlepower amps aren't safe - cool.

[luvdunhill]

So basically you are saying singlepower amps aren't safe - cool.

fair assumption, yes.