[John Williamson]

On 11/02/2021 11:29, Don Pearce wrote:

When he shouted at me in his last post he said that everything was
disconnected, I quote

"Obviously "the DAC having its own wall plug ground" has absolutely
nothing to do with it SINCE I EXPLICITLY STATED THAT THE THING IS
DISCONNECTED FROM EVERYTHING."

So the block diagram is kind of irrelevant. Presumably nothing is
coming out of anything and it (I presume the speaker) is doing this
all on its own. In other words he has a powered speaker that is not
totally silent with an open circuit input. This is not news to me.

He claims that with an open circuit, he gets the normal white noise we
all expect, but when he connects the speaker input to the output on the
converter, he gets an audible hum. There is a pair of domestic standard
(And quality) RCA phono connections on the converter, so the only thing
I can suggest is that the shields on the two phono leads are making an
earth loop connecting the two speaker inputs and the two phono sockets,
which share an earth on the adaptor circuit board. The speakers will be
sharing the safety earth of the whole system with each other. Going from
a single ended output to a balanced input with no isolating transformer
won't be helping.

Either that or he thinks that turning the power off at the wall also
disconnects the safety earth for the Bluetooth adaptor.

I am using a similar Bluetooth adaptor to connect a car amplifier
feeding a pair of speakers to the computer, and have no hum problem at
all unless there is a poor connection between the amplifier and adaptor,
when the jack plug has moved a fraction. Push it back in and peace is
restored. Power for the amplifier is not connected to any earth, as it
runs off 12 volts, and the Bluetooth adaptor is also fed by an isolated
supply. The quality is good enough for an initial rough mix.


--
Tciao for Now!

John.