Systematic error in folowing 3 entries

For some reason the MD-421 - Canford step up - EF183 - started sounding bass heavy.


This may be to bad resistive, capacitive contact cleaning itself.


Or the grid of the EF183 may had been blocked and unblocked it self?, Today and previous day sound started off fine and withing 3 minutes of tube operation bass heaviness suddenly came to play without apparently touching anything.


Trying to compensate for bass a few Pleiades filters were added. (200Hz and higher up to 800Hz) But when the deep bass was cut remaining treble was too high.


So it was decided to remain at the 419mH Canford primary inductance and add a second low cut pole adjusting the coupling capacitor from the EF183 anode to the disco mixer mic input.


22nF made the sound clear as it had been before.


This indicates that 2 different low cut filters need to be used.


Same principle seems to apply to the Grampian ribbon mic. Of course much lower primary inductance will be needed.


Further experiments need to be made including connecting an EMI RS106A which is a 12dB per octave Low Cut and High Cut filter.

Extra bass reduction for ribbon mics

Using the Grampian ribbon mic on various experiments it was best found to low cut with a Pleiades filter or transformer of about 2.3mH input inductance.  This value gives a natural mid and treble production. Of course it can be fine tuned according to need


Further low cut if needed may best be done by other ways, in our experience nets it was done by varying the coupling capacitor from anode to mixer a series resistor of 10nF to the usual 1uF was typically used.


The Sennheiser MD -421 does not need a extra low cut the
Pleiades 19.5mH giving an excellent bass responce at a mic - mouth distance of less than 1 inch. This may sound contradictory with following entry with Canford input transformer of 419mH. At 19.5mH even cutting all treble, the bass still sounds unexagerated. More work needs to be done to decide. The MD421 inherent bass cut makes the experiment more difficult.


Electromagnetic compensation due to the inductor short circuiting the low frequencies is very effective as a pop and wind filter.


The extra treble due to close distance exaggeration was not  reduced  with a shunt anode capacitor as described below.

A clip can be heard on YouTube's Pleiades Radio channel 4th broadcast. No treble cut was used and if I remember well a Canford impedance converter (419mH measured primary inductance) was used as step up. This step up as documented is  feeding a EF183 Pleuades 4.5vVbattery pre preamplifier with 3.9Mohms from anode to grid for positive (less negative) bias.

In fact treble cut must have been used as the cable capacitance makes a high cut filter with the Pleiades electron tube preamplifier output impedance.

Treble reduction for correct brain perceived voice production and reproduction

The experiment below was also done with a Sonotone crystal microphone connected directly to the grid of EF183 electron tube through a 220nF coupling capacitor.


Since the Pleiades connected EF183 with a resistor from anode to grid has an approximate 100k input impedance, bass is already compensated thanks to  the microphone's effective series output capacitance (making a low cut filter with the 100k impedance.


The excellent sound was high cut with a anode shunt capacitor of the order of 10 to 33 nanofarads.


The Grapian ribbon mic with 2.3mH Pleides input transformer did not need much any treble reduction as natural sound was already there.


There was some exceeds bass which could be further cut with a 10nF coupling capacitor from anode to the mixer mic input.

High Frequencies must also be reduced for natural voice production

A Pleiades filter or Pleiades step up transformer can be used to reduce unnatural bass frequencies due to

Soft speaking or singing (voice effort compensation)

Higher level reproduction (Fletcher Manson curves)

Proximity bass boost of microphone

When we achieve an amazing clear bass on voice we are left with a  high frequency content in voice due to

Soft speaking or singing (voice effort spectrum curves)

Higher level reproduction (Fletcher Manson curves)

Mic obstacle effect (mic is very near exaggerates high frequencies)


One effective way to attenuate HF is to add a capacitor from anode to ground. On the Pleiades EF183 pre amplifier Vb=4.5 volts values of the order of 10nf did a fine good in compensating the treble boost perceived.

Further advantage is the reduction of any hiss left.

Another great advantage would be the rounding of peak limited waveforms when more than one stage of tubes is used. This should give a louder subjective voice at smaller objective waveforms with distortion content reduced due to high cut.


The above one tube stage experiment was done with Sennheisr MD-421 - Pleiades 19.5mH 1H step up bass proximity compensating input transformer - EF183 Ra=15K
Ra-g=3.9M  Ci=220nF Co=1uF - mic input of Realistic Disco Mixer


This perhaps is not a very good example as 19.5mH is too low for MD421 cuting more bass than needed.


Very natural voice sound was produced with Canford Audio impedance converter XJ matching transformer .With MD-421 bass cut setting in the middle, mouth distance at 1in, feeding directly the Realistic disco mixer sound was dull and rather mechanical. Feeding the EF183 Pleiades stage which then fed the mixer the sound was great with full body, great treble and mid, and the easiness associated with electron tube circuits. The input impedance of the positive biased stage from anode to grid with 3.9MOhms should have been about 100K. High frequency content reduction was not needed apart for the subtle effect of the cable shunt capacitance high cut filtering.

What is Fear

Fear is an invention so that some can have a good time at the expense of others.

World Recording Museum

Better title to be found.


After a brainstorming session with Sotiris Moutsatsos and Dina Athanasiou.


Specifications:


1. Restaurant
Only fresh juice and top quality Barley Rusk based food with toppings, musical instrument sweets.


2 Shop, e-shop
Selling vinyl records , sound technology and music related books, top quality audio files etc.


3 Sound Reproduction level
Reproduction systems of all decades from 1920's to future state of the art.


4 Sound Production level
History of all pro sound recording equipment up to state of the art recording studio operating with all gear from 1920s to future demo equipment. Includes synthesizers. Producing recordings for visiting musicians.


5 Live level
Concerts with live binaural streaming, (museum radio station), audience participating etc.


6 Lectures
Top world known producers and musicians invited disclosing their art.


7 R&D Level
Research and development, production of recording equipment, techniques, publications.

Can a Pleiades electron tube Preamplifier be used by NASA as front end detector?

The Pleiades pre amplifier is different in 3 respects.


1 It uses positive bias from plate (anode) to grid via an external high Megohm resistor allowing an electron tube to operate as a low noise-figure amplifier at very small power supply voltage (<10V).


2 It deliberately uses reduced heater voltage reducing electron "boiling" cloud around the cathode which seems to obstruct information extraction.


3 Low voltage operation permits the use of battery or solar panel supply which is the quietest source of energy on our planet with very high bandwidth.


Hopefully the circuit may be a basis of beneficial experiments as a front end preamplifier. This may lead to better resolution pictures on radio telescopes or delving deeper into the past, amplifying the faintest signals of the univesce coming electromagnetically from space.