Dont forget to short out that crazy 1K, 1W resistor that's part of the
internal speaker circuit where the speaker is driven through an
electolytic cap back to the + raw Vcc. I have no idea what this was
all about but you had to have a regulated supply or the unit would hum
due to any ripple on the raw Vcc.. Note that when an external speaker
is plugged in the circuit is now wired correctly to a real ground and
no hum from a non-regulated wall wart. I had to do this on both of the
HF-225s I had. I've yet to figure what Lowe was trying to do here.

Frank