On Thu, 11 Feb 2021 11:02:07 +0000, John Williamson
wrote:
On 11/02/2021 09:58, Don Pearce wrote:
Here's the problem. Your description is confused and confusing. You
talk about speaker wire when you mean phono cable. And why are you
talking about a DAC when it isn't plugged in? It is clearly not a part
of the problem.
Did you look at the picture he posted? It shows a Bluetooth to analogue
converter with an optical connection hiding round the back and a pair of
phono sockets on the front, and as Bluetooth is digital, there must be a
DAC inside it. What he claims is that the system is humming when the
receiver is not connected to anything, is not powered up and is not
plugged in to the wall.
Now let's try to sort out what you really mean. Are you saying that
when your amplifier has an open circuit input, there is a low level
hum? If so, that is absolutely fine. That's what they do. As long as
it goes away when something is plugged in all is well. Get a phono
plug and short the live to the ground. Now plug that in. Is the noise
still there?
He is, as far as I can tell, claiming that when the input to the
speakers is open circuit, there is only white or pink noise, and when he
connects to the unpowered, unearthed, DAC he gets a hum. He is going
from an unbalanced phono output to a balanced input to the active
speakers. Unless he is forgetting about a connection somewhere, I can't
see how anything can be coming out of the bluetooth receiver, which
leaves capacitive coupling to the mains somewhere in the system as the
only explanation.
The other thing I'm wondering is why this is all being copied to the
free.spam usenet group?
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.
d
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