A world class sound with the MD21 and a few electronic components

See also:
http://euroelectron.blogspot.com/2018/08/md21-hn-or-md441-u3-to-ef183-open-grid.html


Using the Pleiades V6 circuit and perhaps further simplifying it:






Signal path, setup:


Male singing voice at 1-2in - Sennheiser MD21 HN - Pleiades V6 with Altec 4722 input transformer - Sony TC-D5 Pro - Sennheiser Hd580


If an MD21 HN or HL is used, it's internal step up transformer can be used to drive directly the grid through Cc only.


In order to reduce bass and treble heaviness due to Fletcher Munson and voice effort curves the elcteon tube is run at low anode current, typically 20μA as this was the optimum value found by listening in real time.


One way to achieve 20μA and fabulous big and natural sound is:


Powering the heater by 3.9V. Leaving grid open and powering anode by 9V. See the above post link.


Or using 3.9V for heaters and plate and a very large value of Rag or a large value of Rcg (cathode to grid). This option has not been tested yet.



The sound is everything one could expect from a world class serup. Very clear sound. Big sound, natural across the whole frequency spectrum (flat frequency response from producer's brain to listener's brain), extreme sensitivity, low noise, impressive signal to noise ratio. A ticking clock could be clearly heard on headphones from a far away room.