I have audio card with Hi-Fi input, but it is strictly stereo TRS (not balanced).
I have condenser microphone with balanced TRS output.
I found that mic output is very low, and I receive too much noize from its shield.
I need to connect microphone with galvanic isolation to drop all noize, so it should have absolutly clean zero level. I know it is capable of at least 50 dB of SNR, but now only 15 dB.
I opened mic, everything looks good, it is supplied with small (passive) powering scheme inside, involving few small transistors.
Ok, I have done some research and came to conclusion, I just used condenser mic without any power supply (hehe).
After some considerations I came up with this scheme.
Am I right to not connect shield from everything to GROUND/MIC_IN of sound card?
I will probably use batteries to achieve perfect noize-free environment.
Any recommendations on using capacitors before amplifier?
Best Answer
You haven't given any datasheet link for the microphone so this is all a guess.
The simplest solution is a microphone transformer.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Microphone "unbalancer" and impedance matching.
A really good transformer is expensive and some active circuits may give better frequency response for the same money. The big advantage with the transformer solution is that no power is required.
Figure 2. A typical microphone impedance matching transformer. No messing!
It now appears that the microphone is a 48 V electret. This usually means that it is phantom powered.
simulate this circuit
Figure 3. Rough schema for a balanced line microphone to unbalanced hi-Z input.
The usual scheme for a balanced line, phantom-powered microphone is as shown in Figure 3.