MD21 HN or MD441 U3 to EF183 open grid or cathode return

The Sennheiser MD21 is understandably one of the best microphones on the planet.


It must be said that the ticking clock in the far away room could be very clearly heard. Best yet.


While testing the EF183 at open grid and 9V at the plate on the Pleiades V6 amplifier fed by the MD441 U3...





In this setup...:


http://euroelectron.blogspot.com/2018/08/ef183-grid-at-space-potential-and-plate.html


Some treble reduction at open grid possibky due to only 20μA anode current called for MD21 as it is a bright mic.


The sound was amazing at just 20μA. Great bass, mid, treble balance. Very low noise. What a mic.


When the 18MΩ resistor was returned to positive cathode for little pull up bias the anode current went to 70μA and there was an increase in bass ambient rumble as expected due to a lower impedance anode driving the same Pleiades 10:1 output transformer.


The 20μA grid at space potemtial was much prefered as rumble is gone, voice bass heaviness is gone and there is just a pure full singing voice.


The MD441 sounds perhaps better at 70μA then 20μA, in treble detail at least, due to increased brightness but becomes bass heavy due to proximity effect, Fletcher Munson. Voice effort curves.


The 70μA anode current gives lower amplifier noise but at 20μA both mics can be used closer, the MD21 HN at 1-2in so the signal to noise ratio actually increases considering the system as a whole from signer's vocal chords or singer's brain to listener's brain.


A few hour later addition: after re listening the MD441 sounds bright enough. All that has to be done is moving a bit further away from the mic.


The EF183 on Pleiades V6 with Vh=3.9V, Vb=9V, open grid is one of the best and most natural sounds so far. Anode current is only 20μA. But what a current.