linuxaudio.org

On 05/15/2012 06:10 PM, Fons Adriaensen wrote:

quoted text
> On Tue, May 15, 2012 at 12:07:36PM +0200, Robin Gareus wrote:

>

>> 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.

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..
>> What is not clear to me is

quoted text
>> 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.

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

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