"active gnd" is a "supply splitting" method to avoid output coupling caps with a single supply amp (or the similar passive AC gnd + resistive divider)
above I posted a link to a "proper" connection of an "active gnd" with a "star gnd"
"3-channel" separates the input signal gnd from the output gnd - the output gnd is a "active gnd" usually using the same type of amplifier stage as the R/L channels
using the input reference (which may be a lower current "active gnd" like the TLE2426) to the "3rd-channel" as the signal input and feedback gnd and connecting the headphone gnd to the output of the 3rd-channel amplifier is a where I believe they've taken a wrong turn
the thread you (diditmyself) pointed to has other problems but I chose these 2 AMB posts which I think summarize the "3-channel" difference
Quote:
Originally Posted by amb /img/forum/go_quote.gif
The ear is at the same time an extremely sophisticated instrument that it has an extraordinarily wide dynamic range and (coupled with processing in the brain) have uncanny capabilities such as picking out a single conversation in a very noisy room. However as a measurement device it is also crude and easily fooled by preconceived notions and psychoacoustics.
Your analogy of the stage play doesn't really work here, because the "performance" of the play is a subjective matter. If the goal of an amplifier is to accurately amplify what comes in (i.e., straight wire with gain), then subjectives don't really come into play. Either there is a difference in the reproduced signal or there isn't, and if there is, it should be measurable with proper instrumentation and methodology. Whether any such differences are audible is a whole 'nother matter.
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so we now have a criteria that can be decided entirely on engineering terms - AMB votes for accuracy
unfortunately the last part of the following is easily shown to be wrong on accuracy terms when applied to "3-channel" topology:
Quote:
Originally Posted by amb /img/forum/go_quote.gif
To relate back to the original subject of this thread -- with active ground and class A providing totally constant power supply currents, the capacitors on the rails are not called upon to do much other than keeping the impedance low.
I should also mention that constant PSU draw isn't the only benefit of active ground and balanced topologies. I've often posted about how not dumping load return current into ground eliminates signal ground pollution, but here is a fresh perspective of the synergy between active ground and class A operation that shouldn't be overlooked.
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in the "3-channel" configuration the signal is amplified by the R/L amplifiers relative to the input signal gnd, the output current of the R/L channels passes through the headphone drivers and flows into the output of the 3rd channel - so the voltage appearing across the drivers is
input signal * gain - 3rd-channel output
3rd-channel output differs from "0" (= signal and feedback gnd) by the the noise, output Z*I_r+l of the 3rd channel amp and the distortion caused by 3rd channel amplifier nonlinearity while sinking that current
elsewhere "3-channel" advocates have argued that the errors of the 3rd channel output can cause distortion cancellation or other euphonic changes, tuning the "sound" - a frank admission of divergence from accuracy
my claim is that my illustration of "star gnd" shows that "gnd pollution" can be avoided by purely passive means - which doesn’t introduce a 3rd amplifier's noise, output Z or distortion and can be more accurate
