The Class D amplifier was a great idea but the problem was increased interference when using a large coil, Class A B amplifiers that use common amplifier topography generate high levels of hiss type background noise and this is particularly bad using metal detectors with low threshold volume. We came up with a high quality class B design that has next to zero hiss and generates no extra noise. It only draws 5 milli amps with no input and thus has no noticeable effect on battery drain. This is a winner, to be released soon.
