Voltage and impedance connecting test equipment to Motu M2 DAC

[jrussell88]

Hi all, I have a measurement tool which I'd like to use on my speakers.

It outputs 10V max with an impedance of 100Ω via a BNC connection and I'd like to connect it to my Motu M2 Dac to get the readings into REW for analysis.

The M2 offers XLR for Mic In and TRS for line / guitar on a combined socket with a volume control. There's also a Midi In.

The XLR socket has an impedance of 2.65kΩ and should accept up to 10mV. TRS is 1MΩ single-ended or 2MΩ dual-ended. It should probably accept up to 1V as it's line level.

As I have some spare XLR connectors, I'd prefer to use those.

Can I just put a resistor in series with the XLR socket, 2.65MΩ (= 2.65kΩ x 10V / 10mV) to reduce the voltage, or is there a better way of doing this?

TIA

 

[staticV3]

According to Motu, the M2 can accept up to 10dBu (2.45Vrms) via XLR and up to 16dBu (4.89Vrms) via 1/4" TRS:


In Amir's testing, the TRS was clipping at 10dBu for some reason so you may have to change something in the menu to get the full 16dBu.

 

[jrussell88]

@staticV3 Thanks for clarifying that. So a 8kΩ resistor in series with the test output should reduce the voltage to the correct range.

The test equipment outputs DC, but the M2 appears to have a filter below 20Hz - comments on Amir's review of V1 mentioned 470uF capacitor in series with the XLR 250kΩ-45Ω gain resistor - so should take care of the DC offset.

Is there any reason, such as the impedances, to arrange it differently?