carlmart
100+ Head-Fier
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- Apr 22, 2009
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I'm talking more in the "3 channel active ground" kind of implementation (like the Pimeta https://tangentsoft.net/audio/pimeta2 ) rather than just using an opamp or similar just to set a virtual ground reference though there are a lot of drawbacks especially in terms of noise to that approach but the AD8066 seems to work really well in terms of producing something that is pleasing to listen to even if from an engineering perspective there are a few negatives to the amp design itself.
The Pimeta does implement a virtual ground with an opamp, the TLE2426, only more compactly packed. For headphone drivers it's a simpler powering system, certainly better than using two batteries in portables, using the mid junction as ground. Those batteries may discharge differently and cause power unbalances. The other way is to use a DC-DC supply to generate the +/- voltages. Using the TLE is a simpler way to do that that may work on such circumstances.
I built an amp (somewhat along the lines of the PBA https://www.head-fi.org/threads/pseudo-balanced-amplifier-pba.553236 ) that uses one AD8066 per audio channel, with a fully isolated ground per channel, with the headphone drivers sitting across the outputs of the two amps in the package and it takes the AD8066 to another level again.
The additional circuit for the ground amplifiers allows more current to be used, which is the limitation of the TLE and essential for hungry headphones.
For a very good representation of what active ground means and why would this be better than regular 2-channels headamps, Dr. Meier Corda has a dedicated webpage here: http://www.meier-audio.homepage.t-online.de/grounds.htm.
Balancing a signal can be interesting, particularly if the grounding can't be kept absolutely zero. You could use a balancing chip to feed the separate drivers with more isolation, or a transformer. But of course, you would need to recable the headphones. But most quality headphones that I know of already have two-wires for each driver, that only get together on the connector. There wouldn't be any-rewiring.