Signal path, setup:
Male singing voice at 4-8in - Sennheiser MD441 U3 - Pleiades V6 with Altec 4722 input transformer, 7586 at 1.3V plate potential - Sony TC-D5 Pro - Sennheiser HD580
Great natural sound. Seems very low noise.
The ticking clock in a far away room could be distiguished from ambient noise, hiss (thermal electric noise) through headphones.
No bass, treble exaggeration. Connecting a 0Ω XLR link the hiss goes way down. Then connecting a link between between transformer secondary to ground makes a very subtle difference in hiss. Perhaps it should make more difference. Connecting a 200Ω wire wound resistor XLR link,
the thermal noise increases slightly. When the excellent MD441 U3 is connected all sorts of ambient acoustic noise can be heard. The above is some indication that most of what is heard as hiss is from acoustic rather than electronic (electron fluctuation) noise. More investigation is needed in an acoustic quieter environment.
At 4-8in singing voice sounds flat frequency response from singers brain to listener's brain.
Pull up or Pleiades bias resistor is 6MΩ.
Potential at grid wire is -140mV.
A variation of this schematic is used:
This is a recheck in preparation for substituting the 7586 Nuvistor electron tube to 2DV4 for 1.3V operation for both heaters and plate with just one AA battery (in series with a fuse for safety). Will it work?
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