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DAC+ ADC pro: mixer settings for recording from jumper J4

Hi !

I made an adapter from connector J4 to two XLR female, and now I'm connecting two Sennheiser MD421 dynamic microphones.

I find that in addition to setting the ADC gain (which seems to be remote-controlling the PGA Gain {Left,Right}), I need to set ADC {Left,Right} Input to VIN{L,R}2[SE].

It works, but since the noise level is only ok rather than excellent, I'm wondering: am I running the inputs single-ended ("[SE]"), i.e. unbalanced? There are options [{VIN{1,2}P, VIN{1,2}M}[DIFF]], which I would assume means "differential" i.e. balanced, but they give me a very loud hum with lots of interference.

Can you clarify?

Also, there are two jumpers on the board to the left and right of the mini-jack socket, which must be set to provide a microphone bias voltage. How high is that voltage, and where exactly does it occur? Is it a phantom power between +/- and GND, or a line power between + and GND? Or something else? What is the voltage, and how much power can be drawn? Given the price of this board, I'm a bit reluctant to fry one to find out :)

If those jumpers set the mic bias voltage, then what does ADC Mic Bias do (can be on, off, or with bypass resistor).

Regards, J

 

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