What I am about to write here is similar to third hand information. I do not have first hand experience. I looked into putting an audio loop into a venue. I asked an audiologist about the prevalence of T-coil equipped hearing aids. She told me most users prefer small and rechargeable. There is not much space in the unit and rechargeable would likely be selected. So, the T-coil does not get included. She thought T-coi…
From first hand: No special transconductance(no idea what that means) amplifiers are necessary, just a wire loop that matches output impedance of usual audio amplifier, as described in the article. Hearing aid manufacturers and audiologists prefer their proprietary solutions so they push for removal of T-coil.