I called Brad at Garrett and was told that ALL headphones WILL NOT work with the adapter without a little fandagling...If your phones do not work, there are 2 items you need to purchase...a 1/4" MONO to 1/4" Stereo adapter, or a 1/4" Mono to 1/8" Stereo adapter depending on your headphones plug size, and an Inline Volume Control extension cable...Both of these can be had at ANY electronic supply store...The ATs need a certain impedance in the headphones to deactivate the speaker, and some stereo plugs will not make proper contact inside the adapter cable to shut the speaker off...These 2 items should solve your problems...
I want to see Garrett add a volume control to future adapters to eliminate this problem...Or include the extension and adapter with the headphone adapter...
HH,