Amek Angela - 8 kHz Noise From Master Channel

[scott2000]

It's still unclear to me what the setup looks like. The inputs and outputs to/from each device?
It may not be relevant but some combinations where pins 1 and 3 are shorted vs pin 3 floating can create weirdness depending on circuit topologies?

 

[smilan]

330R is arguably a bit high of a value;

The schematic asking for 300R-1K for R1 and R2, what value would you choose?

no capacitors though?

I connected it with two 110uF bi polar caps as in the schematic you shared here.

Also, with the impedance-balanced connection, you have the option of disconnecting the ground wire from either end of the cable (check which end disconnected gives you the least amount of noise).

I've also tried to disconnect one side (at the time) of the balancing circuit from ground with no change in the noise.

It's still unclear to me what the setup looks like. The inputs and outputs to/from each device?

The Angela outputs are unbalanced with pins 1+3 tied together.
The Motu 16A have balanced inputs with the usual configuration of pin 2 +, pin 3 - and pin 1 ground.
I've tried to connect the Angela outputs with either balanced and un balanced cables with no difference in the noise level.

 

[scott2000]

The Motu 16A have balanced inputs with the usual configuration of pin 2 +, pin 3 - and pin 1 ground.

I was more thinking about where there might be a connection somewhere that is possibly goofing with a circuit that might require pin 3 floating when unbalanced. Usually it's like if the motu outputs are cross coupled or not for instance.
Just having a hard time visualizing what exactly is being used in your setup. Like is the motu even being used for outputs.. etc...
May not even be relevant..

 

[smilan]

I made more testing during the last couple of days and the noise is getting stronger as the sample rate is getting higher.
you can see the differences here:

I took those screenshots with nothing connected to the Motu inputs.
So it seems like something going bad with the Motu at high sample rates.