The great books of Harry F. Olson

Anyone wishing to go deeper into how microphones are designed should search for the excellent books of Harry F. Olson.


Electrical analogies of acoustical and mechanical systems throughout. So that patent reading on the classic microphones can be better understood.


His classic Elements of Acoustical Engineering was the basis of the BBC Engineering Training Series, Microphones book as it is stated in its first pages.


Other examples of amazing books by Olson:


Dynamical Analogies.


Music, Physics and Enginerring,


Acoustical Engineering which must be the 3rd edition of the previously mentioned book.


And many more.


It is also interesting to see the parent list of Olson on Wikipedia. For example there is one on improving the sensitivity of ribbon microphones.

The best RCA ribbon and lowest noise mic ever made?

It is described and tested by Olson on a classic JASA Olson paper.


Olson went as far as putting it inside a vacuum chamber so that the electromotive force (noise) produced by the motion of the diaphragm (ribbon) due to the thermal agitation of molecules imprinting upon the diaphragm (ribbon) could be measured.


It is very interesting that an electron tube head amplifier was prefered to be used instead of a FET because of its lower noise and absence of thermal noise.


Reference:


Microphone Thermal Agitation Noise - Harry F. Olson - Journal of the Acoustical Society of America

An amazing booster microphone preamplifier by RCA and Pleiades amplifiers

The RCA type BA-2C microphone booster or pre preamplifier or head amplifier.


So many years ahead of its time.


It is a front end microphone preamplifier so that a ribbon or moving coil microphone can be connected. And it gives fair play to all the low noise and sensitive ribbon and moving coil microphones.


Fair play by giving them a low noise head amp like condenser capsules have inside the microphone itself.


Many details of the RCA microphone booster can be found on the excellent courant website.
http://www.coutant.org/ba2c/index.html


The Pleiades V5, V6 head amplifiers can be thought of as a more modern implementation of such type of amplifiers as they operate with battery and just 4V to 8V typically, including anodes.


It is known that battery operation reduces many aspects of noise in preamps.


On the Pleiades very low noise operation is further helped by the very low anode and heater voltage. Minimising secondary electron emission effects etc.


Operation at such low voltage is possible by the anode to grid few Megohms biasing resistor.


A 2 stage stage with potentiometer in between can be derived.


Or perhaps a 3 stage with a saturating inter stage transformer for instanteniously peak limiting. Thereby simulating analog magnetic tape recording. See other euroelectron posts.


A three stage head or front end amp could be arranged as follows.


The mic drives through the input transformer the first tube.


A big interstage transformer feeds the second electron tube.


A small interstage transformer driving the 3rd electron tube provides recording preemphasis or peak saturation limiting.


The 3rd tube with high cut implemented (mathematical integration), like a reel to reel tape playback amplifier.


An output transformer creates low output impedance and the adjustable low level but loud sounding output of the booster preamp can then feed an ordinary mic preamp.


This may be called the Pleiades V7.


Pleiades concepts and schematics are open source.


References:

RCA BA2C on www.coutant.org
http://www.coutant.org/ba2c/index.html


Pleiadws V5 or V6 schematic


Neumann U47 schematic

The lower Va (anode voltage) the lower Vh (heater voltage)?

Quite possibly so.


It can be seen on all electron tube textbooks, cathode temperature vs anode voltage curves, for example for diodes.


Would it be possible to operate an EF98 or EF97 with just 1.5 volts for both the heater and anode circuit? On a Pleiades V6 configuration?


Or is the EF183 triode connected the best electron tube on the planet?


Reference:


Pleiades V6 schematic

Testing a microphone is a great psycho acoustic experiment

It may for example involve how it performs in an environment from singer's vocal chords to listener's brain.


And therefore this test does not involve only a mic. It may be a mic, an input transformer, a head amp or prepreamp,..,and how all these interact.


The monitoring system quality is extremely important.


On the Pleiades experiments the Sennheiser HD580 precision headphones are used.


Reference:


Flat frequency response from actor's. singer's vocal chords to listener's brain, Sound picture recording and reproducing characteristics - Loye, Morgan

Collecting microphones is very addictive

Is it a bit like trying many sex partners until the perfect one is found? And one seems never to be satisfied and the search goes on..


And some microphone shapes can be a phalic symbol. Why should men collect mics? They already have one!


Microphones are great converters of molecule vibration to electron vibration.


But we must not forget that all we humans need is love.


It is so often that what we were trying to find had already been there.


Reference:


We are trying for something that has already found us
Jim Morrison

AKG D112 to Pleiades V6 to Sony TC-D5 Pro

Very nice combination.


The D112 microphone has a frequency response curve very similar to Neumann U47.


The V6 is similar to the Neumann U47 head amplifier.


An amazing sound. Full bass but not heavy, great mid, fantastic treble detail.


Signal path, setup:


Male singing voice at 7in - D112 - V6 - TC-D5 Pro - Sennheiser HD580


The inout transformer used inside the Pleiades V6 has an input inductance of 140mH to compensate for proximity effect, and a turns ratio of 10.


References:


Frequency response curves of U47, D112


Pleiades V6 schematic


Neumann U47 schematic