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Discussion Starter #1
I'm a hobbyist and after some experimentation (around 4 years) I want to connect my signals I create on the breadboard to my expensive audio interface. Until now I was using the "mic" input on my laptop to connect the signals and I haven't damaged it. I'm using a 40k resistor in series with each of my 2 signal(s).

I create my signals with a "modular synthesizer" running on an arduino due, DACs and with low-voltage op-amps (mcp6002-4) and I power my circuit with the due's power supply (3.3V).

Now my "expensive audio interface, a DSP platform that costs around 4k euros, has two mic/DI inputs (located at the same plug) with just these specifications:

"2 x MC (switchable phantom power), 2 x instrument input with impedance transformer, adjustable input level 2 x Mic, Hi-Z or Line XLR/jack phantom power 48 V (switchable)"

So I would appreciate some info about the power of the mic/line inputs in general.

Should I take any precautions electrically so to avoid damage the line inputs of my audio interface and the low voltage signals of my audio experimentation circuit? (will activating phantom power accidentally, destroy my circuit and Arduino? Does it pass through the unbalanced 1/4 jack?)

Are the 40k resistors a good value?

Can you point me to an article that discusses line connections, levels, impedance, phantom power, direct boxes etc.

EDIT: The mic input (the physical) takes an XLR cable but at the center there is a hole that takes a jack input. It is labeled as MIC/DI. The signals appear at the same hardware source module in the software. So to make it clear: I don't want to connect to "mic" input but at "DI" line instrument input (which is located at the center of the MIC XLR cable. I suspect phantom power only goes via the XLR cable (3 pins)

The hardware also has balanced line inputs but I'm using these to connect a secondary audio interface.

Lastly: Should I measure the voltage at the audio interface inputs with my multimeter?
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