If just an inductor is connected to a microphone bass heaviness dccreases but sound may become thin. See Pleiades L filters.
If an inductor in series with a resistor is connected to a mic the bass heaviness disapears while body is preserved. See Pleiades (R,L) filters. The reason is that this high pass filter is a gentle slope one, less than 6dB per octave. So bass response is preserved.
It was found experimentally by adjustable Pleiades Danbridge (R,L) filters that directional mics also having the bass boost proximity effect need a smaller value of resistance since they are even more bass heavy for vocals. Ie a less gentle slope is needed but still less than 6dB per octave low cut or high pass. The value of R could typically be 1/10 of the mic impedance. For example a 200Ω mic could be connected to a 20-30 ohm resistor in series with a say 40mH inductor. See for example last week's post on MD441 U3.
On the other had few months ago it has been found that an MD441 U3 could be connected to a broadband input transformer and bass heaviness for intimate vocals be reduced by using anode currents say less than 10μA on the front end booster amplifier. See for example Pleiades V6 operated with just a 1.5V battery and the 2DV4 electron tube. The 2DV4 operated giving a natural bass with no bass heaviness at 1.5V for both heaters and anode. Pleiades bias from anode to grid was used in order to free electrons from positive due to electron emission cathode.
Since at low anode current anode resistance increases, a high cutoff frequency is created similar to using a 40mH inductance at directly to a 200ohm mic. Here the cutoff frequency is created by a few Kohm electron tube plate resistance and output transformer input inductance. But the resistance for the primary winding plays the role of making the slope gentle as it creates a (Pleiades R,L) filter.
The primary winding resistance may not be large but may be enough to satisfy the 10:1 impedance relation of optimum slope of low cut for directional mics.
Is this the reason why just a few microamperes as a front end booster amplifier gave a correct, flat frequency response from producer's brain to listener's brain?
The only drawback was somewhat increase of hiss as at such conditions the electron tube is too ridiculously starved.
Which is the best way? Increasing anode current to say 47μA by using say 3.8V for anode supply and adding a Pleiades (R,L) filter at the mic output? This is very low noise. Or also winding an input transformer with resistance wire? One disadvantage of resistance wire is that such wires may not sound correct and are difficult to solder.
Later addition:
Another solution could be having a 47μA anode current at say 3.7V potential which is enough or perfect for low noise and making the output transformer air core wound. The resistance of the wire will create a Pleiades R,L filter therefore a gentle high pass slope. See also:
https://euroelectron.blogspot.com/2019/04/an-air-wound-ring-se-output-transformer.html
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