[John Doe[_2_]]

https://images-na.ssl-images-amazon....AC_SL1500_.jpg

Nothing is connected to that optical input DAC. No power. No signal. Nothing.
Doesn't matter whether the antenna is connected or not.

With the powered speaker (JBL LSR305, -10dVB, volume maximum) input
disconnected, with its speaker wire dangling from its input, there is almost 0
sound from the speaker except an extremely faint wind sort of sound with my
ear up against it.

Humming begins when the speaker wire is plugged into the disconnected DAC.

Why is that? The DAC isn't connected to anything else. Does it act as a
receiver/antenna?

The humming sound is low enough so it makes little difference, but it is
noticeable.

Thanks.