Getting a new microphone

Why this article?

Recently, I got the opportunity to buy at a discounted price this microphone : Sony ECM-MS907.
In the past, for my recordings, I always used the one on my headset or my phone's.

Sony ECM-MS907 microphone

This Sony mic is stereo, it needs a AA battery (electret), has a 3.5mm jack (TRS). It's of course unbalanced. It has a 1 kOhm impedance.
It was originally made to be used with Sony's camcorder and dictaphones. I wanted it to use it with my computer.

I'm writing this article to share my audio knowledge as I encountered a problem and succeeded to make the mic works (with lots of researches).

The problem

I plugged it on my computer's sound card. The microphone port allows it to be amplified (not line-in). My Realtek card accepts stereo microphone input.

First recording, sound level is low.
I raise to 20 dB amp in the configuration panel.
Second recording, we can hear my voice if I'm standing very near.
30 dB is a little better but with lot of noise.

I realized few days after that (just like professional microphones) it needed to be amplified.
To compare, you usually have and output in milivolts on a headset and microvolts on this kind of microphones.

To be sure the microphone was working, I managed to plug it on an old stereo system. Noise level was very high, no stereo, but I could hear people few meters away.
I could have used the headphones plug directly to the line-in of my sound card but the signal was terrible (lots of noise).

The solution

I started to look for a preamp. It's something quite common but I didn't want to invest into something over a 1000 € (mostly profesionnal products).

Furthermore, it needed to be two channels (stereo), which is less common. I didn't want to buy two mono amplfiers.

If possible, that could be powered externally (not only main AC).

I was sure about one thing : I would have to buy an adapter (3.5mm jack to 6.35mm/RCA/XLR...).

I had to verify if the voltage of the microphone was acceptable for a preamp input.

Jack Connectors

More informations about the jack connector.

Balanced/Unbalanced

symétrique/asymétrique in french

When I read datasheets of preamps, I realized it mentionned balanced and unbalanced inputs.
To improve sound quality, microphones are outputing a same signal on a "stereo" jack (TRS), they are inverted (or symetric).
It helps reconstructing a better signal based on this inversion instead of the ground.

The ECM-MS907 is not a common microphone. You usually encounter mono-balanced and XLR or 6.35 TRS jacks.

It would have given me weird results if I plugged a 2 channels on a balanced input.

The product

There it was, the USB Dual Pre, less than 100 €. Provides multiples plugs for monitoring.
On Windows, it appears as a soundcard for mic and phones with a standard driver (nothing installed).
Can be powered by USB, main AC or battery (though from what I read the amplification might not very good with the battery).
The inputs are two 6.35 jack (TRS) and XLR (with phantom power). AND they can be balanced (TRS jacks) or not (TS jacks).

USB Dual ART Pre

I also had to buy an adapter (3 €) to convert my 3.5mm stereo jack (1/8 TRS) into two 6.35mm mono jack (1/4 TS).
These types of cables are called insert (a french link): they split the ouput (balanced → unbalanced, stereo → mono...).

Finally: Gain is great, very low noise, great quality with the microphone at ~30 dB gain.