At your risk. Please take all safety precautions. For example soldering fumes must not be inhaled, solder must only be touched with gloves, listening to playback with headphones must be at a very low level,...
On this example....
1
A Shure SM58 Mexico microphone is used for male singing voice at 24in from mouth, mic pointing towards the nose. Microphone placed much higher than head. At 24in there is almost no bass boost proximity effect. The mic is used outdoors (balcony) in order to avoid recording thousands of annoying, blurring short delayed reflections from walls.
2
A step up signal transformer is used to step up the microphone voltage and impedance. So at this stage the signal level is like a condenser capsule with the added advantage of the much less harmonic or non linear distortion at high frequencies (see older posts with references). The step up transformer used was a 1 to 10 step up ratio with a low primary inductance (typically 280mH) which further corrects bass. This is a low value of inductance so the mic can be used a bit closer or a higher inductance transformer can be used while keeping the mic at 24in. But it all depends on song, register and singer. The transformer stops RF energy picked up by the mic cable and the step up process creates a unique low noise (hiss) recording. The transformer used is a German one inside an female to male XLR barrel.
3
The high impedance signal is connected directly to the Gate of a JFET. A K117 JFET is used. The Pleiades K117 mic preamplifier is built inside the female XLR connector. For more details, schematic please see older posts a few yeas back. The circuit is as minimal as it can be for purest sound and lowest noise. Just a K117 JFET, a resistor connected to the Source terminal for bias and nothing else. Amplified signal is taken from the Drain terminal. The load resistor where the amplified voltage is developed is in the following circuit which also supplies the 1 or 2 volts needed to power the low noise JFET preamp. The other end of the cable is connected to a 3.5mm male headphone mic jack connector.
4
An Apple 3.5mm (headphone, mic) to USB C adaptor is connected. It was bought for 10euros in Athens Public shores. It contains all needed ADC for mic and DAC for headphones.
5
A Galaxy mobile phone is connected at USB C
6
Recording made with the camera app of the mobile phone.
7
That's it.
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