This is the schematic of the head amp used with the difference that Cc is 22nF as usual, Pleiades bias resistor is usually 6MΩ when an EF183 or Nuvistor 7586 electron tube is used. A Nunvistor 7586 was connected and its heater was connected directly to 3.9V. (No series droping resistor). 3 AA rechargeable 1.2V Sanyo Eneloop batteries are used. A series fuse should always be used for safety.
Signal path, setup:
Male singing voice - Sennhsiser MD21 HN at 1-2in - (Pleiades L,R filter) - Pleiades V6 Nuvistor in breadboard with Altec 4722 input transformer and Pleiades 10:1 output transformer (see relevant post) - Sony TC-D5 Pro XLR mic in mono mode - Sennheiser HD580 warn by singer as usual
In the beginning no mic was connected, then the heater voltage was applied to Pleiades V6. After a while some hiss could be heard from the open input Pleiades V6 through the headphones. It happened to be raining. Then the mic was connected and so much sound and detail came out of it, it was scary. The MD21 can act as a vacuum cleaner sucking sound from everywhere. Very impressive. The Nuvistor giving a very big sound with almost no noise.
The sound was bass heavy for intimate vocals due to Fletcher - Munson, voice effort curves etc.
Then the Pleiades (130Ω,40mH) serial number 18062416, see relevant post, which was supposed to be 140Ω,40mH was connected between mic and Pleiades V6 input. Immediately the sound was balanced.
Then the experimental Pleiadss 145Ω,42mH was connected (this is made up with cable clips etc). It sounded great too. Less midrange than the (130Ω,40mH). So the 130Ω sounded more clear, the 145Ω more full bodied.
It may be a good thing that the 130Ω,40mH Neutrik module Pleiades filter has not been changed to 145mH as it sounds more suitable for the MD21 HN than for the MD211 N.
References:
Flat frequency response from producer's to listener's brain, Sound Picture Recording and Reproducing Characteristics - D. P. Lowe, K. F. Morgan - JSMPE
The Pleiades 140Ω,40mH microphone filter - euroelectron
http://euroelectron.blogspot.com/2018/06/the-pleiades-14040mh-microphone-filter.html
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