Do electron tubes behave as bass, mid compressors (automatic gain control) wity grid leak resistor dectating release time?

At your risk. Take all safety precautions.


For some strange reason it sounds better reducing bass, mid heaviness due to proximity effect and well known psychoacoustic phenomena after the electron tube rather than before it.


Considerng the following signal paths:


male singing voice - mic - Pleiades (R,L) low cut filter - mic input transformer - electron tube preamp - output transformer - main mic preamplifier - headphone amplifier - monitoring headphones - listener's brain


It sounds nice.


But the following may sound even better:


male singing voice - mic - (Pleiades (R,L) filter) - mic input transformer - electron tube starved at low anode voltage, very low anode current - output transformer - main mic preamp - headphone amplifier - monitoring headphones - listener's brain


Bass cut in the 2nd example is mainly produced by the high electron tube internal anode output impedance interacting with output transformer primary inductance. [MIT staff]


Why does bass cut after the electron tube sounds better than before it?


In order to understand the compressing effect of electron tubes reference is to [Armstrong].


Even a world class mic or especially a world class mic can sound amazingly horrible by bass heaviness on a flat frequency response setup. We know the reason why is that the objective is not flat frequency response from mic to loudspeaker but from producer's brain to listener's brain [Lowe, Morgan].


But how do electron tubes do the trick of transforming a horrible sound feeding them to a very listenable sound that could even be a standard hit song sound quality, listened, enjoyed by so many listeners on the radio?


How do they transform crapiness to gold?


Some relevant experiments are described on recent posts on the one electron tube Pleiades V6 CV2269 mic booster amplifier.


Is a possible explanation that the low uncut signal has a larger envelope thereby creating greater rectification effect at grid. This DC changes bias to more negative and therefore decreases gain. Release time of the compressing effect is dictated by the grid bias or grid leak resistor. Low cut is implemented by the output transformer. So effectively we have a compressor with boosted bass or mid frequency (compressor side chain) content due to proximity effect etc at side chain. Flat frequency response to listener's brain is effected by said interaction of electron tube with output transformer.


Or is it just the gentle slope bass or treble reduction from the output's transformer interaction with electron tube?


Or both?


Or other reasons?


References:


Magnetic Circuits and Transformers - MIT staff


Operating features of the Audion - E. H. Armstrong


Sound picture recording a reproducing characteristics - D. P. Lowe, K. F. Morgan - Journal of the Society of motion picture engineers