Professional radio broadcasting dynamic microphone

Microphone SHURE SM7B is a great piece of electronics since it's fit to working in high electric and magnetic field environment, for example - a radio studio. The Microphone has got even four windings(coil). The main sound capsule winding, compensational coil (meant to compensate for the outer magnetic field), and two for frequency response characteristics correction. You can adjust the high and low frequencies around 10 dB. Directional characteristic is cardioid. To reduce mechanical interference the cartridge was mounted into a rubber air pillow. The microphone is simply ideal for HAM Radio purposes. The only problem is the small sensitivity that needs to be compensated with higher amplification. Photo above.

ICOM transceivers are prepared for microphone amplification. The microphone's input has a power voltage that is received through the external amplifier load's resistor. That lets us use a simple microphone amplifier circuit.

The amplifiers distortions with the THD output level up to -20 dBu (about 70 mV rms) aren't above 0,04%. It raises up to 1% with 1V rms. ICOM IC-7700 microphone input is calibrated to 10 mV rms with the output power set to 200 W. So we have around 20 dB reserve from overload with only 0,04 % distortions. A real hi-end piece of audio equipment. The frequecy responce characteristics are 50 Hz - 10 kHz with -1 dB, then it's specially limited to 330n and 10n with the help of capacitor. 10n cpacitors with 180 Ohm resistors create a high frequency filter limiting the level of these frequencies in the input and output of the microphones' amplifier.

The amplifier was tested with a sound generator with a THD not higher than 0,008% to 1V rms and Fire Wire TERRATEC 24 Bit/192 kHz audio interface. Software - SpektraPro.

The assembly and the model might look amateur, but they do not have any influence to the parameters and it works pretty well. The amplifier is mounted on a KENWOOD MC-90 microphone stand.

 

Another microphone from my collection is Marshall MXL V69 Mogami Edition Tube Microphone.