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.
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.
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