A head amplifier with Fletcher Munson, voice effort, proximity effect compensation

For example it could be the Pleiades V6 head amplifier with EF183 or 7586 Nuvistor. A Altec, Jensen, Sowter or hand made nanoperm Magnetec, Mumetal, Permalloy, Supermallow etc. core manufacturers that come to mind are Magnetec, Magmet, Arnold, Haufe.





Assuming the inductances of both transformers are high enough we can go down very low in frequency. This may be useful for recording a pipe organ for example.


If an omnidirectional microphone is connected no proximity effect exists. If voice or other instrument is still bass heavy or treble heavy due to Flether-Munson (high acoustic reproduction) or voice effort curves (soft singing voice) the following passive filter can be connected in parallel ie to pins 2,3 or input of the head amplifier. An inductor L in series with R for a gentle slope low cut or high pass. And again in parallel a capacitor is series with R for gentle slope high cut or low pass. The high cut may also be done after the secondary and then a small value of C will be needed. Both resistors can be variable producing any slope desired. L adjusts turnover frequency together with the mic output impedance. Same for C. So 2 parametric filters can be made inside the head amp.


If a directional microphone such as ribbon, or moving coil unidirectional is connected the following addition filter may be needed. An inductor in parallel again with pins 2,3. It's value will depend on the mic, the type of singing, the mic impedance and how close the distance of mic to source. Different again switchable values may be used and the process may be paralleled with the focusing adjustment on camera, macro settings for example.


All these Pleiades filters do not normally interfier with the quality of the mic's signal. The microphone is always connected to pins 2,3 ie straight to the head amp input. The passive Pleiades filters just remove what is not needed ie are subtractive.


Switches can be arranged such that anything can be in or out.


No make up gain may be needed as all these passive filters do is remove what is not sanded to aproach ideal of flat frequency response from producer's brain to listener's brain [Lowe, Morgan]. An ultra low noise head amp such as the Pleiades V6 may only make things better.


The Pleiadss filters can also be external to the head amp. For example they may be implemented inside XLR female to male barrels. Neutrik modules cylindrical or larger rectangular ones are recommended as they are functionally and aesthetically perfect.


D


Reference:


Flat frequency response from singers vocal chords to listener's brain, Sound Picture Recording and Reproducing Characteristics - D. P. Lowe, K. F. Morgan - JSMPE