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I really wasn't talking about a battery-powered amp like the Mini^3 which has a battery DC supply which is obviously incapable of having anything except a virtual ground without going to single-supply topology with output caps.
can you explain how you can call any properly implemented signal ground anything different to a proper split battery supply? i.e. one that uses an even number of 2 or more batteries and taps the 'ground' reference from the middle directly, rather than relying on resistors, caps, regulators, opamps or some other lossy mechanism to create a reference that is half the rail voltage.
ground is imaginary and you can just as easily have a dc coupled battery powered device as a dc coupled ac powered device. ground is just a concept to help visualise current flow, given proper signal and return routing the actual voltage of 'ground' with reference to '0' is meaningless as long as its consistent, sufficiently low impedance and with at least the same current sinking ability as current sourcing ability (connected directly this by definition must be true). quality batteries are now low enough impedance that contact resistance will swamp any impedance of the power source.
I run a fully dc coupled balanced portable dac/amp with 4 x lifepo4 cells in series as a +/-6v6 nominal centre tapped psu that supplies a fully regulated dual mono bipolar power supply for the output stage as well as various regs for the dec and other digital supplies. 'ground' is 6.6vdc with reference to 0 and there is absolutely no DC across the rails at the balanced headphone out, because in this case the balanced AC signal rides on DC with reference to the 'ground'. The sabre dac (AVCC/2) and IV stage/headamp are dc coupled just as the headphones are, but as its balanced there is none across the output. I'm taking a bit of a risk with my jh13 there, but not really, as i'm running opa1632dgn differential chips and any dc error even in a failure condition is likely to be common mode and a disconnect of one wire would just mean an incomplete signal.
Edited by qusp - 10/13/11 at 12:38pm
