Apogee D/A 16x ground problem

[ilfungo]

Hi
I'm tryng to connect Apogee D/A 16x to my console Amek M2000 but something strange happen.
My configuration:

Apogee A/D 16 come from direct output
Apogee D/A 16 go to line return on Amek

If i record something without line return connected ( d/a 16 to line in ) the sound is clear and no noise is audible, if
them are connected Buzz and hum come in.

It's ground loop?
I've tried all configuration ( same ground point between apogee and Amek, apogee with ground disconnected and Amek connected....)
What can I try?
Suggestions?
THANKS!!!

PS. attached Amek channel schematics

 

[ilfungo]

???

 

[Sammas]

How are the tie-lines between the apogee's and amek wired?

Ideally you only want the shield connected at one end in such a situation.
If you are connecting your apogees straight to the console, I would only connect the shield at the console end.

 

[ln76d]

Do you have original manual which came with your console?
If not, this could be helpful:
http://forum.analogconsole.com/downloads/Amek%20M2000.pdf
Seems to be many features as optional and may be different for each model.
Did you tried both line inputs?
Reffering to the manual - i didn't found any definition of "direct output"?!?
Are you sure that your channel is based exact on this schematic?
Check that  your M2000 has unbalanced line input or output, maybe you need configure apogee for unbalanced mode and use this type of connection.

 

[johnheath]

I have a Apogee Quartet and soon after I bought it I noticed some typical ac hum in my studio monitors. I tried to find the source of this for quite some time until I realized that it came from the dc supply to the apogee itself. I changed the chord to a 8 inches shielded chord and also connected the supply from another room in my flat since I realized there was a ground loop inside my flat.

Now it is dead quiet… so it might be useful to see if it is the same problem… very cheap

/John

 

[ilfungo]

Thanks for all answers!!!
Hi  ln76d
I've just seen all the console connections and on my line input are configured as unbalanced...
The schematics are correct , I will try to rearrange the line input as balanced.
The line input use the same transformer as mic input,can I do this?
Thanks!!!

 

[ln76d]

It's hard to tell especially if there is no resistors values at the line input and pad.
Try on one channel, for example line 1, to disconnect ground between "42" and "43" points (with the ground on "42" only). It could make mismatch in input impedance. You can easily compare it to line 2 input - wire as usual second output from apogee with the same signal on both. If this wouldn't work, try to omit input resistors and use the pad (i don't know what level it can down - 20dB or more?), but this could not work well probably lower impedance and too high level.