20130302 / 20150215

    Use as:
Nearly invisible high quality stage floor microphone. Opera, operetta, drama with good AB stereo. 
Piano (taped onto the inside of the lid) open, warm bright, neutral sound. 
TV discussions: with only two flat microphones on a conference table, good stereo separation, absense of phasing (sound coloration) and clothing noises. Resulting in good AB stereo and understanding even when talking together at the same time.

    Properties (Phase Coherent Cardioids) :
Directivity : half cardioids.

Large "reach" due to extra 6dB suppression of room-reverb (indirect -reflected- sound).

10dB negative feedback in capsules internal FET (created by pa0nhc line driver design), results in 10dB lower distortion,

    Sensitivity and dynamic range :
Total electronic gain = 0dB (+10db gain - 10dB feedback) 
    + 6dB acoustic gain (as PCC)
        Practical sensitivity as floormike: -35dBv/Pa +-4dB 
            Max. balanced audio output : +1dBv, 
                calculated max. sound pressure (1kHz) : 130dBspl +- 4dB.
                (10dB higher maxSPL compared to some commercial PCC microphones)
                        On top of that 15dB output reserve in electronics.

        Noise and hum :
Transformerless design, especially optimized :
    Very unsensitive to cable induced hum and noise after one simple adjustment.
        up to 60dB cable noise suppression between 50Hz-50kHz with three carefull matched components. 

If the 3 critical component pairs are only of standard 1% standard tolerance : 
    60dB @ 1.5kHz and 40dB or better from 50Hz to over 50kHz are obtainable.

Very flat and wide overall frequency response 50Hz-15kHz (after simple correction of the  low frequency response).

Output impedance: really 2x 200 Ohms from 25Hz to 50kHz, in parallel with 2x 4700pF. Prevents noises from RF signals in the microphone cable.

Unsensitive to shocks and vibrations. Back-electret super cardioid microphone element 9.7mm dia.  (Needs simple modification). 

Phantom power: 48V 2x 1.4mA. 

    PCB design:
Single sided.
Standard components (no SMD).
Fits inside a 50.5 x 50.5 mm small, cheap diecast box.