At your risk.
This is just an inductor in series with resistance and the total connected across a microphone's output i.e. pins 2,3.
Since there is also the output impedance of the mic, usually about 350 ohms in SM58 case, there are 2 time constants together with the inductor, one dictating the frequency below which the filter starts to attenuate and the other dictating the frequency where bass drop starts to shelve.
Objective is to create flat frequency response from producer's to listener's brain in a very simple and effective way, small size, no added noise, no power consumption, no hum pickup etc.
This is one of the first attempts to make a compact filter that sounds as good as the Cinema Engineering 4031B at -12db 100Hz, +4dB 10kHz settings.
Serial number, date time code: 25031714
Format: inexpensive XLR female to male cylindrical adaptor
Lettering color: Magenta to signify high pass in analogy with visible frequency spectrum
Core used: Small Siemens Epcos ferrite toroid
Date time code of making ferrite inductor: 25030508
Diameter of enameled wire used: 0.16mm
Number of turns: 100 (using a wooden thin stick)
Inductance: 25 mH
Series resistors used: 2 each 36 ohms (possibly metal film, good quality made in Germany), each resistor on either side of inductor wire terminals for balanced symmetry
Frequency response test: Source impedance approx. 200 ohms, terminating impedance 10kOms:
10KHz: +3dB
1.5KHz: 0dB
550Hz: -4dB
200Hz: -6.5dB
!00Hz: -7dB
0dB is -60dBV
Subjective test: Signal path: male voice singing beginning of Bridge over Troubled Water - Simon & Garfunkel verse -Shure SM58 at 24in above head - Pleiades (74Ω,25mH) - SONY TC-D5M - TDK SAX - Sennheiser HD580 or Pleiades 2N3053 driving Celestion Ditton 150
It sounded fairly close to Cinema Engineering EQ but without insertion loss which is an added advantage.
It remains a mystery why Pleiades filters tend to very gently boost 10KHz which may be another surprise advantage.
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