15 May
2012
15 May
'12
8:44 p.m.
On 05/15/2012 06:10 PM, Fons Adriaensen wrote:
Here it mainly concerns the outputs: In my case there's a ground loop
between my Screen (Asus VE278) and the active speakers when connected
via computer and an USB UA-25 (not UA25-ex which features a ground-lift
switch) -> 1/4inch TRS -> B2031A speakers.
Disconnecting either the screen or the speakers (and using headphones)
works, otherwise there's a hum on the system; luckily no sparks, no
x-runs, either :)
A multimeter shows a constant 1mA current and ~3-4mV AC potential.
(measured between the USB-shielding of the PC and the disconnected
USB-cable of the UA25) when the screen is connected.
Both the screen as well as the speakers (and computer) are connected to
the same power-stripe and share the ground.
Fun-fact: When disconnecting the screen the potential between USB and PC
goes up to ~150mV (IFF the computer is not battery powered otherwise
it's 0) but the current drops to nil.
/me is pondering to cut the ground-wire from the screen.. but I have so
far refrained from doing that.
Anyway at some point the interface may end up on stage somewhere and
ground-lifting may be required for the inputs, too. Although in that
case I'll likely have some ground-lifting DI-boxes around.
robin
On Tue, May 15, 2012 at 12:07:36PM +0200, Robin Gareus
wrote:
Excuse my newbie question, but I'm not experienced with SPDIF.
Can one [word-clock] sync two devices using SPDIF or ADAT and still use
the analog I/O on both? -- Is that hardware specific or is there a
standard for that?
I assume the master-device will need to send a signal via SPDIF.
I'll check later if the 1818VSL can do both: output to SPDIF and analog
at the same time. but I don't know if I can do that remotely. What I do
already know is that the clock-source for each input can be configured
individually. but I'm still waiting for Brian to connect the device. my
ssh login already works..
It has only balanced outputs but otherwise fits
the bill.
Usually you can use them as unbalanced. In some cases this
requires a special cable, but that's unlikely.
What seems weird with with this box: it has a
word-clock out but no
word-clock input.
Not a real one, but it will sync to SPDIF or ADAT. What is not
clear to me is
if the balanced I/Os are [or can be] ground-lifted.
Better not. Ground lifting can damage your inputs unless
1. the inputs are physically isolated by a transformer
(not the case),
2. the common mode voltage (the difference between the two
grounds) is small.
Unless you have transformer isolation, you need a more or less
common ground. And then, if the inputs are really balanced and
you use balanced cables, there is no need to lift the ground.